Knowledge

Homography

Source 📝

2733: 3830: 2019: 1250: 153: 1402:
geometry, the homographies and the collineations of the projective line that are considered are those obtained by restrictions to the line of collineations and homographies of spaces of higher dimension. This means that the fundamental theorem of projective geometry (see below) remains valid in the one-dimensional setting. A homography of a projective line may also be properly defined by insisting that the mapping preserves
1228: 4157: 824: 2413:
The composition of two central collineations, while still a homography in general, is not a central collineation. In fact, every homography is the composition of a finite number of central collineations. In synthetic geometry, this property, which is a part of the fundamental theory of projective
2535:
As all the projective spaces of the same dimension over the same field are isomorphic, the same is true for their homography groups. They are therefore considered as a single group acting on several spaces, and only the dimension and the field appear in the notation, not the specific projective
1401:
of the points of a projective line is a collineation, since every set of points are collinear. However, if the projective line is embedded in a higher-dimensional projective space, the geometric structure of that space can be used to impose a geometric structure on the line. Thus, in synthetic
805: 2508:, the first part is an easy corollary of the definitions. Therefore, the proof of the first part in synthetic geometry, and the proof of the third part in terms of linear algebra both are fundamental steps of the proof of the equivalence of the two ways of defining projective spaces. 1223:{\displaystyle {\begin{aligned}y_{1}&={\frac {a_{1,0}+a_{1,1}x_{1}+\dots +a_{1,n}x_{n}}{a_{0,0}+a_{0,1}x_{1}+\dots +a_{0,n}x_{n}}}\\&\vdots \\y_{n}&={\frac {a_{n,0}+a_{n,1}x_{1}+\dots +a_{n,n}x_{n}}{a_{0,0}+a_{0,1}x_{1}+\dots +a_{0,n}x_{n}}}\end{aligned}}} 3545: 3833: 105:. The term "projective transformation" originated in these abstract constructions. These constructions divide into two classes that have been shown to be equivalent. A projective space may be constructed as the set of the lines of a 397:
of a finite number of perspectivities. It is a part of the fundamental theorem of projective geometry (see below) that this definition coincides with the more algebraic definition sketched in the introduction and detailed below.
612: 1366: 3904: 3092: 3415: 3714:
In older treatments one often sees the requirement of preserving harmonic tetrads (harmonic sets) (four collinear points whose cross-ratio is −1) but this excludes projective lines defined over fields of
829: 617: 3167: 3442: 269:
if extended to projective spaces. Therefore, this notion is normally defined for projective spaces. The notion is also easily generalized to projective spaces of any dimension, over any
93:, which, etymologically, roughly means "similar drawing", dates from this time. At the end of the 19th century, formal definitions of projective spaces were introduced, which extended 2489:
is the composition of an automorphic collineation and a homography. In particular, over the reals, every collineation of a projective space of dimension at least two is a homography.
1711:
It follows that, given two frames, there is exactly one homography mapping the first one onto the second one. In particular, the only homography fixing the points of a frame is the
3299: 2038:
are related by several central collineations, which are completely specified by choosing a line of fixed points L passing through the intersection of the lines ABCD and A
129:); in this context, collineations are easier to define than homographies, and homographies are defined as specific collineations, thus called "projective collineations". 121:
for the study of homographies. The alternative approach consists in defining the projective space through a set of axioms, which do not involve explicitly any field (
2496:. In particular, if the dimension of the implied projective space is at least two, every homography is the composition of a finite number of central collineations. 1397:
In the study of collineations, the case of projective lines is special due to the small dimension. When the line is viewed as a projective space in isolation, any
144:
are supposed to be true. A large part of the results remain true, or may be generalized to projective geometries for which these theorems do not hold.
800:{\displaystyle {\begin{aligned}y_{0}&=a_{0,0}x_{0}+\dots +a_{0,n}x_{n}\\&\vdots \\y_{n}&=a_{n,0}x_{0}+\dots +a_{n,n}x_{n}.\end{aligned}}} 2748:. A, B, C, D and V are points on the image, their separation given in pixels; A', B', C' and D' are in the real world, their separation in metres. 2782:
The cross-ratio of four collinear points is an invariant under the homography that is fundamental for the study of the homographies of the lines.
132:
For sake of simplicity, unless otherwise stated, the projective spaces considered in this article are supposed to be defined over a (commutative)
1284: 2217:
are those in which the center is not incident with the axis. A central collineation is uniquely defined by its center, its axis, and the image
3851: 3550:
was interested in periodicity when he calculated iterates in 1879. In his review of a brute force approach to periodicity of homographies,
2981: 3361: 4063: 4010: 4182: 3111: 2423: 1394:. These correspond precisely with those bijections of the Riemann sphere that preserve orientation and are conformal. 4142: 4081: 4029: 3992: 3540:{\displaystyle h^{n}={\begin{pmatrix}1&n\\0&1\end{pmatrix}}={\begin{pmatrix}1&0\\0&1\end{pmatrix}}.} 2303:
The geometric view of a central collineation is easiest to see in a projective plane. Given a central collineation
4016:, translated from the 1977 French original by M. Cole and S. Levy, fourth printing of the 1987 English translation 180:, and, specifically, the difference in appearance of two plane objects viewed from different points of view. 4177: 3335: 2720:, whose blocks are the sets of points contained in a line, it is common to call the collineation group the 2504:), the third part is simply a definition. On the other hand, if projective spaces are defined by means of 2090:. It is a part of the fundamental theorem of projective geometry that the two definitions are equivalent. 4161: 2932: 137: 62:
asserts that is not so in the case of real projective spaces of dimension at least two. Synonyms include
20: 1624:, and this basis is unique up to the multiplication of all its elements by the same nonzero element of 383: 1233:
which generalizes the expression of the homographic function of the next section. This defines only a
480:, may thus be represented by the coordinates of any nonzero point of this line, which are thus called 1480:
are considered in this section, although most results may be generalized to projective spaces over a
247: 3938: 3178: 2456: 394: 82: 2086:, they are traditionally defined as the composition of one or several special homographies called 1391: 4113: 4055: 2897: 2540: 2452: 1780: 1383: 481: 113:(the above definition is based on this version); this construction facilitates the definition of 3716: 3608: 2968: 2745: 141: 114: 2297: 176:
Historically, the concept of homography had been introduced to understand, explain and study
1540:
be the canonical projection that maps a nonzero vector to the vector line that contains it.
4135: 4124: 3959: 2609: 2521: 2300:. It is an elation, if all the eigenvalues are equal and the matrix is not diagonalizable. 570:
This may be written in terms of homogeneous coordinates in the following way: A homography
177: 8: 4047: 3343: 3323: 2756:
The width of the side street, W is computed from the known widths of the adjacent shops.
2741: 2525: 1262: 419: 270: 133: 110: 27: 2942: 2501: 2433: 2083: 1716: 811: 575: 228: 184: 126: 122: 102: 86: 3331: 1278:). With this representation of the projective line, the homographies are the mappings 4138: 4077: 4059: 4025: 4006: 3988: 3433: 3418: 2675: 2613: 1902:(consisting of the elements having only one nonzero entry, which is equal to 1), and 2524:
of two homographies is another, the homographies of a given projective space form a
1855:), results in multiplying the projective coordinates by the same nonzero element of 3951: 3102: 2670:
acts on the eight points in the projective line over the finite field GF(7), while
1422: 1415: 1234: 407: 262: 224: 39: 4121: 3955: 3327: 2765: 2517: 1719:(where projective spaces are defined through axioms). It is sometimes called the 1274: 94: 77:
Historically, homographies (and projective spaces) have been introduced to study
51: 2732: 2529: 2213:
are the central collineations in which the center is incident with the axis and
2209:, but not necessarily pointwise). There are two types of central collineations. 602:. The homogeneous coordinates of a point and the coordinates of its image by 4105: 3551: 2950: 2576: 2505: 1387: 227:
was originally introduced by extending the Euclidean space, that is, by adding
118: 3172:
but otherwise the linear fractional transformation is seen as an equivalence:
818:(projective completion) the preceding formulas become, in affine coordinates, 4171: 3845: 3829: 3547: 3312: 2809:
form a projective frame of this line. There is therefore a unique homography
2493: 2427: 2129: 2082:
In above sections, homographies have been defined through linear algebra. In
1481: 1254: 255: 78: 3347: 2717: 2647: 2105: 1712: 815: 106: 98: 55: 43: 1361:{\displaystyle z\mapsto {\frac {az+b}{cz+d}},{\text{ where }}ad-bc\neq 0,} 3899:{\textstyle \scriptstyle {\begin{pmatrix}a&b\\c&d\end{pmatrix}},} 3576:, then it is elliptic, and no loss of generality occurs by assuming that 2777: 2737: 1403: 1398: 508: 35: 1249: 2376:
that does not belong to ℓ may be constructed in the following way: let
2293: 2285: 2145: 1238: 549:, define the same homography if and only if there is a nonzero element 401: 2018: 172:
are related by a perspectivity, which is a projective transformation.
152: 2455:(over a projective frame) of a point. These collineations are called 2432:
There are collineations besides the homographies. In particular, any
526: 266: 47: 2716:. When the points and lines of the projective space are viewed as a 2074:
of a point E by this collineation is the intersection of the lines A
2682:, is the homography group of the projective line with five points. 19:
This article is about the mathematical notion. For other uses, see
3087:{\displaystyle U{\begin{pmatrix}a&c\\b&d\end{pmatrix}}=U.} 1272:
and a point, called the "point at infinity" and denoted by ∞ (see
3640: 3305: 1455: 3410:{\displaystyle h={\begin{pmatrix}1&1\\0&1\end{pmatrix}}} 231:
to it, in order to define the projection for every point except
4156: 4117: 425:
may be defined as the set of the lines through the origin in a
59: 58:. In general, some collineations are not homographies, but the 2424:
Collineation § Fundamental theorem of projective geometry
2128:, but this term may be confusing, having another meaning; see 3558:
A real homography is involutory (of period 2) if and only if
2417: 1918: 595: 2261:) and the intersection with the axis of the line defined by 2078:
I and OE, where I is the intersection of the lines L and AE.
2744:
to measure real-world dimensions of features depicted in a
2492:
Every homography is the composition of a finite number of
2307:, consider a line ℓ that does not pass through the center 1237:
between affine spaces, which is defined only outside the
2712:
of the collineations of a projective space of dimension
2532:
is the homography group of any complex projective line.
4019: 3861: 3855: 3854: 3768: 3503: 3464: 3376: 3008: 2768:, V is visible, the width of only one shop is needed. 2443:
induces a collineation of every projective space over
4022:
Projective Geometry: From Foundations to Applications
3445: 3364: 3181: 3114: 2984: 2623:
is the group of the products by a nonzero element of
2500:
If projective spaces are defined by means of axioms (
2414:
geometry is taken as the definition of homographies.
1287: 827: 615: 2272:
A central collineation is a homography defined by a
1244: 402:
Definition and expression in homogeneous coordinates
1409: 3898: 3539: 3409: 3293: 3161: 3086: 2470:Given two projective frames of a projective space 1832:. It is not difficult to verify that changing the 1450:of them. A projective frame is sometimes called a 1360: 1222: 799: 261:With these definitions, a perspectivity is only a 2844:to 1. Given a fourth point on the same line, the 810:When the projective spaces are defined by adding 46:from which the projective spaces derive. It is a 4169: 4020:Beutelspacher, Albrecht; Rosenbaum, Ute (1998), 3834:Homographies of associative composition algebras 3162:{\displaystyle z\mapsto {\frac {za+b}{zc+d}}\ ,} 1906:. On this basis, the homogeneous coordinates of 1721:first fundamental theorem of projective geometry 2555:when acting on a projective space of dimension 203:to the intersection (if it exists) of the line 2563:. Above definition of homographies shows that 2478:that maps the first frame onto the second one. 2292:. It is a homology, if the matrix has another 384:Perspectivity § Perspective collineations 3719:two and so is unnecessarily restrictive. See 2953:. Homographies act on a projective line over 2273: 1943:of it, there is one and only one homography 1917:are simply the entries (coefficients) of the 211:. The projection is not defined if the point 2233:and does not belong to the axis. (The image 16:Isomorphism of projective spaces in geometry 3338:can be represented with homographies where 2245:is the intersection of the line defined by 1474:Projective spaces over a commutative field 598:the multiplication by a nonzero element of 4046: 4037: 3804: 3792: 3682: 3587:. Since the characteristic roots are exp(± 2760: 2752: 2466:consists of the three following theorems. 2464:fundamental theorem of projective geometry 2418:Fundamental theorem of projective geometry 379: 60:fundamental theorem of projective geometry 4052:Projective Geometries Over Finite Fields 3353: 2731: 2054:. Let O the intersection of the lines AA 2017: 2013: 1971:. The projective coordinates of a point 1715:. This result is much more difficult in 1443:points such that no hyperplane contains 1248: 183:In three-dimensional Euclidean space, a 151: 4110:Homographies, quaternions and rotations 4071: 3780: 3670: 2654:) then the homography group is written 2485:is at least two, every collineation of 2481:If the dimension of a projective space 147: 4170: 4000: 3985:Linear Algebra and Projective Geometry 3816: 3744: 3658: 3322:. Ring homographies have been used in 3973: 3906:and its connection with the function 3702: 2474:, there is exactly one homography of 1806:on this frame are the coordinates of 215:belongs to the plane passing through 101:by the addition of new points called 4089: 3982: 3756: 3732: 3720: 3698: 3694: 3304:The homography group of the ring of 2511: 1498:be a projective space of dimension 1268:may be identified with the union of 254:of the above projection is called a 2975:) are described by matrix mappings 1983:are the homogeneous coordinates of 1937:of the same dimension, and a frame 1430:of a projective space of dimension 1386:, which can be identified with the 42:, induced by an isomorphism of the 13: 4112:, Oxford Mathematical Monographs, 4099: 4040:Foundations of Projective Geometry 3769:Beutelspacher & Rosenbaum 1998 2803:on a projective line over a field 301:that may be obtained by embedding 199:is the mapping that sends a point 14: 4194: 4149: 3221: 2124:(traditionally these were called 1926:. Given another projective space 1847:, without changing the frame nor 1377:linear fractional transformations 1245:Homographies of a projective line 4155: 4074:Fundamental Concepts of Geometry 3828: 3569:. If it is periodic with period 3105:, the homography may be written 2722:automorphism group of the design 1795:; the projective coordinates of 1784:: every point may be written as 1410:Projective frame and coordinates 525:. Such an isomorphism induces a 356:, with a different center, then 3945: 3839: 3822: 3810: 3798: 3786: 3774: 2627:of the identity matrix of size 2159:), which is fixed pointwise by 1241:where the denominator is zero. 537:), because of the linearity of 4042:, New York: W.A. Benjamin, Inc 4024:, Cambridge University Press, 3762: 3750: 3738: 3726: 3708: 3688: 3676: 3664: 3652: 3285: 3273: 3258: 3246: 3230: 3227: 3218: 3185: 3118: 3078: 3045: 3000: 2988: 2926: 2727: 2539:Homography groups also called 2197:), which is fixed linewise by 2120:that maps lines onto lines. A 1390:, the homographies are called 1291: 487:Given two projective spaces P( 448:may be represented by a point 117:and allows using the tools of 1: 3967: 3294:{\displaystyle U\thicksim U.} 2674:, which is isomorphic to the 2253:and the line passing through 2229:that differs from the center 370:to itself, which is called a 3336:conformal group of spacetime 1955:onto the canonical frame of 380:§ Central collineations 277:Given two projective spaces 7: 3634: 2933:Projective line over a ring 2872:, denoted , is the element 2516:As every homography has an 2144:, such that there exists a 1890:consisting of the image by 1514:-vector space of dimension 1261:The projective line over a 1257:preserve orthogonal circles 495:) of the same dimension, a 444:has been fixed, a point of 21:Homography (disambiguation) 10: 4201: 4072:Meserve, Bruce E. (1983), 4038:Hartshorne, Robin (1967), 2930: 2900:over the projective frame 2775: 2421: 1994:on the canonical frame of 1896:of the canonical basis of 1413: 507:), which is induced by an 324:a central projection onto 191:(the center) onto a plane 18: 4183:Transformation (function) 4132:Geometry: An Introduction 3978:, Interscience Publishers 2575:may be identified to the 2457:automorphic collineations 2349:. The image of any point 594:. This matrix is defined 541:. Two such isomorphisms, 484:of the projective point. 273:, in the following way: 242:, which does not contain 68:projective transformation 3983:Baer, Reinhold (2005) , 3939:Messenger of Mathematics 3646: 2971:. The homographies on P( 2961:), consisting of points 2541:projective linear groups 1458:in a space of dimension 592:matrix of the homography 374:, when the dimension of 336:is a perspectivity from 138:Pappus's hexagon theorem 4056:Oxford University Press 4001:Berger, Marcel (2009), 2898:homogeneous coordinates 2453:homogeneous coordinates 2357:is the intersection of 2205:is mapped to itself by 2093:In a projective space, 2022:Points A, B, C, D and A 1781:homogeneous coordinates 1576:such that the frame is 1554:, there exists a basis 1384:complex projective line 482:homogeneous coordinates 156:Points A, B, C, D and A 72:projective collineation 4090:Yale, Paul B. (1968), 3900: 3848:(1879) "On the matrix 3541: 3411: 3295: 3163: 3088: 2969:projective coordinates 2785:Three distinct points 2773: 2746:perspective projection 2311:, and its image under 2079: 1776:projective coordinates 1392:Möbius transformations 1362: 1258: 1224: 801: 378:is at least two. (See 330: 309:in a projective space 195:that does not contain 173: 115:projective coordinates 4092:Geometry and Symmetry 3901: 3542: 3412: 3354:Periodic homographies 3296: 3164: 3089: 2890:. In other words, if 2735: 2697:is a subgroup of the 2685:The homography group 2241:) of any other point 2225:) of any given point 2088:central collineations 2021: 2014:Central collineations 1862:The projective space 1436:is an ordered set of 1373:homographic functions 1363: 1252: 1225: 802: 366:is a homography from 348:a perspectivity from 275: 155: 54:to lines, and thus a 4164:at Wikimedia Commons 4136:Wadsworth Publishing 4134:, page 263, Belmont: 4130:Gunter Ewald (1971) 4048:Hirschfeld, J. W. P. 3960:Mathematical Reviews 3852: 3554:gave this analysis: 3443: 3362: 3179: 3112: 2982: 2610:general linear group 2122:central collineation 2112:is a bijection from 1285: 1253:Homographies of the 825: 613: 574:may be defined by a 499:is a mapping from P( 372:central collineation 293:is a bijection from 238:Given another plane 148:Geometric motivation 4178:Projective geometry 4005:, Springer-Verlag, 3344:composition algebra 3324:quaternion analysis 2848:of the four points 2742:projective geometry 2614:invertible matrices 2528:. For example, the 1543:For every frame of 1382:In the case of the 476:), being a line in 393:was defined as the 320:and restricting to 265:, but it becomes a 142:Desargues's theorem 28:projective geometry 3974:Artin, E. (1957), 3896: 3895: 3886: 3537: 3528: 3489: 3407: 3401: 3291: 3159: 3084: 3033: 2815:of this line onto 2774: 2699:collineation group 2502:synthetic geometry 2434:field automorphism 2201:(any line through 2084:synthetic geometry 2080: 1717:synthetic geometry 1358: 1259: 1220: 1218: 812:points at infinity 797: 795: 229:points at infinity 185:central projection 178:visual perspective 174: 127:synthetic geometry 123:incidence geometry 103:points at infinity 87:Euclidean geometry 4160:Media related to 4065:978-0-19-850295-1 4012:978-3-540-11658-5 3976:Geometric Algebra 3421:when the ring is 3281: 3205: 3155: 3151: 3065: 2772: 2771: 2676:alternating group 2512:Homography groups 2296:and is therefore 2132:) is a bijection 1774:allows to define 1628:. Conversely, if 1371:which are called 1332: 1331: where  1324: 1214: 1015: 511:of vector spaces 40:projective spaces 4190: 4159: 4095: 4086: 4068: 4043: 4034: 4015: 3997: 3979: 3962: 3952:H. S. M. Coxeter 3949: 3943: 3935: 3934: 3932: 3931: 3922: 3919: 3905: 3903: 3902: 3897: 3891: 3890: 3843: 3837: 3832: 3826: 3820: 3814: 3808: 3802: 3796: 3790: 3784: 3778: 3772: 3766: 3760: 3754: 3748: 3742: 3736: 3730: 3724: 3712: 3706: 3692: 3686: 3680: 3674: 3668: 3662: 3656: 3629: 3606: 3586: 3575: 3568: 3552:H. S. M. Coxeter 3546: 3544: 3543: 3538: 3533: 3532: 3494: 3493: 3455: 3454: 3434:integers modulo 3416: 3414: 3413: 3408: 3406: 3405: 3328:dual quaternions 3321: 3300: 3298: 3297: 3292: 3279: 3257: 3256: 3203: 3168: 3166: 3165: 3160: 3153: 3152: 3150: 3136: 3122: 3103:commutative ring 3093: 3091: 3090: 3085: 3063: 3038: 3037: 2966: 2922: 2915: 2895: 2889: 2882: 2871: 2865: 2859: 2853: 2843: 2837: 2831: 2827: 2821: 2814: 2808: 2802: 2796: 2790: 2750: 2749: 2711: 2696: 2673: 2669: 2665: 2638: 2607: 2595: 2574: 2554: 2409: 2403: 2396: 2389: 2370: 2364: 2336: 2335: 2326: 2320: 2176: 2103: 2077: 2073: 2069: 2065: 2061: 2057: 2053: 2049: 2045: 2041: 2037: 2033: 2029: 2025: 2009: 1993: 1982: 1976: 1970: 1954: 1948: 1942: 1936: 1925: 1916: 1905: 1901: 1895: 1885: 1846: 1831: 1811: 1805: 1794: 1778:, also known as 1773: 1708: 1697: 1645: 1623: 1571: 1553: 1539: 1520: 1509: 1503: 1497: 1479: 1470: 1463: 1449: 1442: 1435: 1428:projective basis 1423:projective frame 1416:Projective frame 1367: 1365: 1364: 1359: 1333: 1330: 1325: 1323: 1309: 1295: 1235:partial function 1229: 1227: 1226: 1221: 1219: 1215: 1213: 1212: 1211: 1202: 1201: 1177: 1176: 1167: 1166: 1148: 1147: 1131: 1130: 1129: 1120: 1119: 1095: 1094: 1085: 1084: 1066: 1065: 1049: 1040: 1039: 1020: 1016: 1014: 1013: 1012: 1003: 1002: 978: 977: 968: 967: 949: 948: 932: 931: 930: 921: 920: 896: 895: 886: 885: 867: 866: 850: 841: 840: 806: 804: 803: 798: 796: 789: 788: 779: 778: 754: 753: 744: 743: 721: 720: 701: 697: 696: 687: 686: 662: 661: 652: 651: 629: 628: 587: 566: 524: 467: 440:. If a basis of 439: 408:projective space 365: 319: 263:partial function 225:projective space 223:. The notion of 219:and parallel to 171: 167: 163: 159: 4200: 4199: 4193: 4192: 4191: 4189: 4188: 4187: 4168: 4167: 4152: 4114:Clarendon Press 4102: 4100:Further reading 4084: 4066: 4032: 4013: 3995: 3970: 3965: 3950: 3946: 3923: 3920: 3911: 3910: 3908: 3907: 3885: 3884: 3879: 3873: 3872: 3867: 3857: 3856: 3853: 3850: 3849: 3844: 3840: 3827: 3823: 3815: 3811: 3805:Hirschfeld 1979 3803: 3799: 3793:Hirschfeld 1979 3791: 3787: 3779: 3775: 3767: 3763: 3755: 3751: 3743: 3739: 3731: 3727: 3713: 3709: 3693: 3689: 3683:Hartshorne 1967 3681: 3677: 3669: 3665: 3657: 3653: 3649: 3637: 3612: 3596: 3577: 3570: 3559: 3527: 3526: 3521: 3515: 3514: 3509: 3499: 3498: 3488: 3487: 3482: 3476: 3475: 3470: 3460: 3459: 3450: 3446: 3444: 3441: 3440: 3400: 3399: 3394: 3388: 3387: 3382: 3372: 3371: 3363: 3360: 3359: 3358:The homography 3356: 3315: 3249: 3245: 3180: 3177: 3176: 3137: 3123: 3121: 3113: 3110: 3109: 3032: 3031: 3026: 3020: 3019: 3014: 3004: 3003: 2983: 2980: 2979: 2962: 2935: 2929: 2917: 2901: 2891: 2884: 2873: 2867: 2861: 2855: 2849: 2839: 2833: 2829: 2823: 2816: 2810: 2804: 2798: 2792: 2786: 2780: 2766:vanishing point 2730: 2701: 2686: 2681: 2671: 2667: 2666:. For example, 2655: 2628: 2597: 2579: 2564: 2544: 2518:inverse mapping 2514: 2494:perspectivities 2430: 2420: 2401: 2394: 2391: 2377: 2368: 2362: 2333: 2328: 2318: 2316: 2177:for all points 2164: 2126:perspectivities 2098: 2097:, of dimension 2075: 2071: 2067: 2063: 2059: 2055: 2051: 2047: 2043: 2039: 2035: 2031: 2027: 2023: 2016: 2003: 1995: 1984: 1978: 1972: 1964: 1956: 1950: 1944: 1938: 1927: 1921: 1907: 1903: 1897: 1891: 1888:canonical frame 1871: 1863: 1842: 1840: 1829: 1820: 1813: 1807: 1796: 1785: 1771: 1762: 1751: 1738: 1727: 1699: 1695: 1686: 1675: 1662: 1651: 1644: 1635: 1629: 1621: 1612: 1601: 1588: 1577: 1570: 1561: 1555: 1544: 1522: 1515: 1505: 1499: 1488: 1475: 1465: 1459: 1444: 1437: 1431: 1418: 1412: 1329: 1310: 1296: 1294: 1286: 1283: 1282: 1275:Projective line 1247: 1217: 1216: 1207: 1203: 1191: 1187: 1172: 1168: 1156: 1152: 1137: 1133: 1132: 1125: 1121: 1109: 1105: 1090: 1086: 1074: 1070: 1055: 1051: 1050: 1048: 1041: 1035: 1031: 1028: 1027: 1018: 1017: 1008: 1004: 992: 988: 973: 969: 957: 953: 938: 934: 933: 926: 922: 910: 906: 891: 887: 875: 871: 856: 852: 851: 849: 842: 836: 832: 828: 826: 823: 822: 794: 793: 784: 780: 768: 764: 749: 745: 733: 729: 722: 716: 712: 709: 708: 699: 698: 692: 688: 676: 672: 657: 653: 641: 637: 630: 624: 620: 616: 614: 611: 610: 606:are related by 577: 558: 512: 472:. A point of P( 465: 456: 449: 434: 414:) of dimension 404: 357: 314: 169: 165: 161: 157: 150: 136:. Equivalently 89:, and the term 24: 17: 12: 11: 5: 4198: 4197: 4186: 4185: 4180: 4166: 4165: 4151: 4150:External links 4148: 4147: 4146: 4128: 4106:Patrick du Val 4101: 4098: 4097: 4096: 4087: 4082: 4069: 4064: 4044: 4035: 4030: 4017: 4011: 3998: 3993: 3980: 3969: 3966: 3964: 3963: 3956:On periodicity 3944: 3894: 3889: 3883: 3880: 3878: 3875: 3874: 3871: 3868: 3866: 3863: 3862: 3860: 3838: 3821: 3809: 3797: 3785: 3773: 3761: 3749: 3737: 3725: 3717:characteristic 3707: 3687: 3675: 3663: 3650: 3648: 3645: 3644: 3643: 3636: 3633: 3632: 3631: 3536: 3531: 3525: 3522: 3520: 3517: 3516: 3513: 3510: 3508: 3505: 3504: 3502: 3497: 3492: 3486: 3483: 3481: 3478: 3477: 3474: 3471: 3469: 3466: 3465: 3463: 3458: 3453: 3449: 3404: 3398: 3395: 3393: 3390: 3389: 3386: 3383: 3381: 3378: 3377: 3375: 3370: 3367: 3355: 3352: 3330:to facilitate 3302: 3301: 3290: 3287: 3284: 3278: 3275: 3272: 3269: 3266: 3263: 3260: 3255: 3252: 3248: 3244: 3241: 3238: 3235: 3232: 3229: 3226: 3223: 3220: 3217: 3214: 3211: 3208: 3202: 3199: 3196: 3193: 3190: 3187: 3184: 3170: 3169: 3158: 3149: 3146: 3143: 3140: 3135: 3132: 3129: 3126: 3120: 3117: 3095: 3094: 3083: 3080: 3077: 3074: 3071: 3068: 3062: 3059: 3056: 3053: 3050: 3047: 3044: 3041: 3036: 3030: 3027: 3025: 3022: 3021: 3018: 3015: 3013: 3010: 3009: 3007: 3002: 2999: 2996: 2993: 2990: 2987: 2951:group of units 2931:Main article: 2928: 2925: 2776:Main article: 2770: 2769: 2762: 2758: 2757: 2754: 2729: 2726: 2679: 2577:quotient group 2513: 2510: 2506:linear algebra 2498: 2497: 2490: 2479: 2419: 2416: 2337:, the axis of 2298:diagonalizable 2185:) and a point 2015: 2012: 1999: 1960: 1904:(1, 1, ..., 1) 1867: 1836: 1825: 1818: 1767: 1760: 1747: 1736: 1698:is a frame of 1691: 1684: 1671: 1660: 1646:is a basis of 1640: 1633: 1617: 1610: 1597: 1586: 1566: 1559: 1530:∖ {0} → 1414:Main article: 1411: 1408: 1388:Riemann sphere 1369: 1368: 1357: 1354: 1351: 1348: 1345: 1342: 1339: 1336: 1328: 1322: 1319: 1316: 1313: 1308: 1305: 1302: 1299: 1293: 1290: 1246: 1243: 1231: 1230: 1210: 1206: 1200: 1197: 1194: 1190: 1186: 1183: 1180: 1175: 1171: 1165: 1162: 1159: 1155: 1151: 1146: 1143: 1140: 1136: 1128: 1124: 1118: 1115: 1112: 1108: 1104: 1101: 1098: 1093: 1089: 1083: 1080: 1077: 1073: 1069: 1064: 1061: 1058: 1054: 1047: 1044: 1042: 1038: 1034: 1030: 1029: 1026: 1023: 1021: 1019: 1011: 1007: 1001: 998: 995: 991: 987: 984: 981: 976: 972: 966: 963: 960: 956: 952: 947: 944: 941: 937: 929: 925: 919: 916: 913: 909: 905: 902: 899: 894: 890: 884: 881: 878: 874: 870: 865: 862: 859: 855: 848: 845: 843: 839: 835: 831: 830: 808: 807: 792: 787: 783: 777: 774: 771: 767: 763: 760: 757: 752: 748: 742: 739: 736: 732: 728: 725: 723: 719: 715: 711: 710: 707: 704: 702: 700: 695: 691: 685: 682: 679: 675: 671: 668: 665: 660: 656: 650: 647: 644: 640: 636: 633: 631: 627: 623: 619: 618: 461: 454: 429:-vector space 403: 400: 389:Originally, a 207:and the plane 149: 146: 119:linear algebra 15: 9: 6: 4: 3: 2: 4196: 4195: 4184: 4181: 4179: 4176: 4175: 4173: 4163: 4158: 4154: 4153: 4144: 4143:0-534-00034-7 4140: 4137: 4133: 4129: 4126: 4123: 4119: 4115: 4111: 4107: 4104: 4103: 4093: 4088: 4085: 4083:0-486-63415-9 4079: 4075: 4070: 4067: 4061: 4057: 4053: 4049: 4045: 4041: 4036: 4033: 4031:0-521-48364-6 4027: 4023: 4018: 4014: 4008: 4004: 3999: 3996: 3994:9780486445656 3990: 3986: 3981: 3977: 3972: 3971: 3961: 3957: 3953: 3948: 3941: 3940: 3930: 3926: 3918: 3914: 3892: 3887: 3881: 3876: 3869: 3864: 3858: 3847: 3846:Arthur Cayley 3842: 3835: 3831: 3825: 3818: 3813: 3806: 3801: 3794: 3789: 3782: 3777: 3770: 3765: 3758: 3753: 3746: 3741: 3734: 3729: 3722: 3718: 3711: 3704: 3700: 3696: 3691: 3684: 3679: 3672: 3667: 3660: 3655: 3651: 3642: 3639: 3638: 3627: 3623: 3619: 3615: 3610: 3604: 3600: 3594: 3590: 3584: 3580: 3573: 3566: 3562: 3557: 3556: 3555: 3553: 3549: 3548:Arthur Cayley 3534: 3529: 3523: 3518: 3511: 3506: 3500: 3495: 3490: 3484: 3479: 3472: 3467: 3461: 3456: 3451: 3447: 3439:) since then 3438: 3437: 3431: 3428: 3424: 3420: 3402: 3396: 3391: 3384: 3379: 3373: 3368: 3365: 3351: 3349: 3348:biquaternions 3345: 3341: 3337: 3333: 3329: 3325: 3319: 3314: 3313:modular group 3310: 3307: 3288: 3282: 3276: 3270: 3267: 3264: 3261: 3253: 3250: 3242: 3239: 3236: 3233: 3224: 3215: 3212: 3209: 3206: 3200: 3197: 3194: 3191: 3188: 3182: 3175: 3174: 3173: 3156: 3147: 3144: 3141: 3138: 3133: 3130: 3127: 3124: 3115: 3108: 3107: 3106: 3104: 3100: 3081: 3075: 3072: 3069: 3066: 3060: 3057: 3054: 3051: 3048: 3042: 3039: 3034: 3028: 3023: 3016: 3011: 3005: 2997: 2994: 2991: 2985: 2978: 2977: 2976: 2974: 2970: 2965: 2960: 2956: 2952: 2948: 2944: 2940: 2934: 2924: 2921: 2913: 2909: 2905: 2899: 2894: 2887: 2880: 2876: 2870: 2864: 2858: 2852: 2847: 2842: 2836: 2826: 2819: 2813: 2807: 2801: 2795: 2789: 2783: 2779: 2767: 2763: 2759: 2755: 2751: 2747: 2743: 2739: 2734: 2725: 2723: 2719: 2715: 2709: 2705: 2700: 2694: 2690: 2683: 2677: 2663: 2659: 2653: 2649: 2645: 2640: 2636: 2632: 2626: 2622: 2619: 2615: 2611: 2605: 2601: 2594: 2591: 2587: 2583: 2578: 2572: 2568: 2562: 2559:over a field 2558: 2552: 2548: 2542: 2537: 2533: 2531: 2527: 2523: 2519: 2509: 2507: 2503: 2495: 2491: 2488: 2484: 2480: 2477: 2473: 2469: 2468: 2467: 2465: 2460: 2458: 2454: 2450: 2446: 2442: 2438: 2435: 2429: 2428:Perspectivity 2425: 2415: 2411: 2408: 2404: 2397: 2388: 2384: 2380: 2375: 2371: 2360: 2356: 2352: 2348: 2344: 2341:is some line 2340: 2331: 2324: 2314: 2310: 2306: 2301: 2299: 2295: 2291: 2288:of dimension 2287: 2283: 2281: 2277: 2270: 2268: 2264: 2260: 2256: 2252: 2248: 2244: 2240: 2236: 2232: 2228: 2224: 2220: 2216: 2212: 2208: 2204: 2200: 2196: 2192: 2188: 2184: 2180: 2175: 2171: 2167: 2162: 2158: 2154: 2150: 2147: 2143: 2139: 2135: 2131: 2130:Perspectivity 2127: 2123: 2119: 2115: 2111: 2107: 2101: 2096: 2091: 2089: 2085: 2070:. The image E 2020: 2011: 2007: 2002: 1998: 1991: 1987: 1981: 1977:on the frame 1975: 1968: 1963: 1959: 1953: 1947: 1941: 1934: 1930: 1924: 1920: 1914: 1910: 1900: 1894: 1889: 1883: 1879: 1875: 1870: 1866: 1860: 1858: 1854: 1850: 1845: 1839: 1835: 1828: 1824: 1817: 1810: 1803: 1799: 1792: 1788: 1783: 1782: 1777: 1770: 1766: 1759: 1755: 1750: 1746: 1742: 1735: 1731: 1724: 1722: 1718: 1714: 1709: 1706: 1702: 1694: 1690: 1683: 1679: 1674: 1670: 1666: 1659: 1655: 1649: 1643: 1639: 1632: 1627: 1620: 1616: 1609: 1605: 1600: 1596: 1592: 1585: 1581: 1575: 1569: 1565: 1558: 1551: 1547: 1541: 1537: 1533: 1529: 1525: 1518: 1513: 1508: 1502: 1495: 1491: 1485: 1483: 1482:division ring 1478: 1472: 1468: 1462: 1457: 1454:, although a 1453: 1447: 1440: 1434: 1429: 1425: 1424: 1417: 1407: 1405: 1400: 1395: 1393: 1389: 1385: 1380: 1378: 1374: 1355: 1352: 1349: 1346: 1343: 1340: 1337: 1334: 1326: 1320: 1317: 1314: 1311: 1306: 1303: 1300: 1297: 1288: 1281: 1280: 1279: 1277: 1276: 1271: 1267: 1264: 1256: 1255:complex plane 1251: 1242: 1240: 1236: 1208: 1204: 1198: 1195: 1192: 1188: 1184: 1181: 1178: 1173: 1169: 1163: 1160: 1157: 1153: 1149: 1144: 1141: 1138: 1134: 1126: 1122: 1116: 1113: 1110: 1106: 1102: 1099: 1096: 1091: 1087: 1081: 1078: 1075: 1071: 1067: 1062: 1059: 1056: 1052: 1045: 1043: 1036: 1032: 1024: 1022: 1009: 1005: 999: 996: 993: 989: 985: 982: 979: 974: 970: 964: 961: 958: 954: 950: 945: 942: 939: 935: 927: 923: 917: 914: 911: 907: 903: 900: 897: 892: 888: 882: 879: 876: 872: 868: 863: 860: 857: 853: 846: 844: 837: 833: 821: 820: 819: 817: 816:affine spaces 813: 790: 785: 781: 775: 772: 769: 765: 761: 758: 755: 750: 746: 740: 737: 734: 730: 726: 724: 717: 713: 705: 703: 693: 689: 683: 680: 677: 673: 669: 666: 663: 658: 654: 648: 645: 642: 638: 634: 632: 625: 621: 609: 608: 607: 605: 601: 597: 593: 590:, called the 589: 585: 581: 573: 568: 565: 561: 556: 552: 548: 544: 540: 536: 532: 528: 523: 519: 515: 510: 506: 502: 498: 494: 490: 485: 483: 479: 475: 471: 464: 460: 453: 447: 443: 437: 433:of dimension 432: 428: 424: 421: 417: 413: 409: 399: 396: 392: 387: 385: 381: 377: 373: 369: 364: 360: 355: 351: 347: 343: 339: 335: 329: 327: 323: 317: 313:of dimension 312: 308: 304: 300: 296: 292: 291:perspectivity 288: 285:of dimension 284: 280: 274: 272: 268: 264: 259: 257: 256:perspectivity 253: 249: 245: 241: 236: 234: 230: 226: 222: 218: 214: 210: 206: 202: 198: 194: 190: 187:from a point 186: 181: 179: 154: 145: 143: 139: 135: 130: 128: 124: 120: 116: 112: 109:over a given 108: 104: 100: 99:affine spaces 96: 92: 88: 84: 80: 75: 73: 69: 65: 61: 57: 53: 49: 45: 44:vector spaces 41: 37: 33: 29: 22: 4131: 4109: 4094:, Holden-Day 4091: 4073: 4051: 4039: 4021: 4002: 3984: 3975: 3947: 3937: 3928: 3924: 3916: 3912: 3841: 3836:at Wikibooks 3824: 3812: 3800: 3788: 3781:Meserve 1983 3776: 3764: 3752: 3740: 3735:, p. 66 3728: 3710: 3690: 3678: 3671:Meserve 1983 3666: 3654: 3625: 3621: 3617: 3613: 3602: 3598: 3592: 3588: 3582: 3578: 3571: 3564: 3560: 3435: 3429: 3426: 3422: 3357: 3339: 3332:screw theory 3317: 3308: 3303: 3171: 3098: 3096: 2972: 2963: 2958: 2957:, written P( 2954: 2946: 2938: 2936: 2919: 2911: 2907: 2903: 2892: 2885: 2878: 2874: 2868: 2862: 2856: 2850: 2845: 2840: 2834: 2824: 2817: 2811: 2805: 2799: 2793: 2787: 2784: 2781: 2738:cross-ratios 2721: 2718:block design 2713: 2707: 2703: 2698: 2692: 2688: 2684: 2661: 2657: 2651: 2648:Galois field 2643: 2641: 2634: 2630: 2624: 2620: 2617: 2603: 2599: 2592: 2589: 2585: 2581: 2570: 2566: 2560: 2556: 2550: 2546: 2543:are denoted 2538: 2534: 2530:Möbius group 2515: 2499: 2486: 2482: 2475: 2471: 2463: 2461: 2448: 2447:by applying 2444: 2440: 2436: 2431: 2412: 2406: 2399: 2392: 2386: 2382: 2378: 2373: 2366: 2365:. The image 2358: 2354: 2350: 2346: 2342: 2338: 2329: 2322: 2312: 2308: 2304: 2302: 2289: 2284:that has an 2279: 2275: 2271: 2266: 2262: 2258: 2254: 2250: 2246: 2242: 2238: 2234: 2230: 2226: 2222: 2218: 2214: 2210: 2206: 2202: 2198: 2194: 2190: 2189:(called the 2186: 2182: 2178: 2173: 2169: 2165: 2160: 2156: 2152: 2151:(called the 2148: 2141: 2137: 2133: 2125: 2121: 2117: 2113: 2109: 2106:collineation 2099: 2094: 2092: 2087: 2081: 2005: 2000: 1996: 1989: 1985: 1979: 1973: 1966: 1961: 1957: 1951: 1945: 1939: 1932: 1928: 1922: 1912: 1908: 1898: 1892: 1887: 1881: 1877: 1873: 1868: 1864: 1861: 1856: 1852: 1848: 1843: 1837: 1833: 1826: 1822: 1815: 1812:on the base 1808: 1801: 1797: 1790: 1786: 1779: 1775: 1768: 1764: 1757: 1753: 1748: 1744: 1740: 1733: 1729: 1726:Every frame 1725: 1720: 1713:identity map 1710: 1704: 1700: 1692: 1688: 1681: 1677: 1672: 1668: 1664: 1657: 1653: 1647: 1641: 1637: 1630: 1625: 1618: 1614: 1607: 1603: 1598: 1594: 1590: 1583: 1579: 1573: 1567: 1563: 1556: 1549: 1545: 1542: 1535: 1531: 1527: 1523: 1516: 1511: 1506: 1500: 1493: 1489: 1486: 1476: 1473: 1466: 1464:has at most 1460: 1451: 1445: 1438: 1432: 1427: 1421: 1419: 1404:cross-ratios 1396: 1381: 1376: 1372: 1370: 1273: 1269: 1265: 1260: 1232: 809: 603: 599: 591: 583: 579: 576:nonsingular 571: 569: 563: 559: 554: 550: 546: 542: 538: 534: 530: 521: 517: 513: 504: 500: 496: 492: 488: 486: 477: 473: 469: 462: 458: 451: 445: 441: 435: 430: 426: 422: 415: 411: 405: 390: 388: 375: 371: 367: 362: 358: 353: 349: 345: 341: 337: 333: 331: 325: 321: 315: 310: 306: 302: 298: 294: 290: 286: 282: 278: 276: 260: 251: 243: 239: 237: 232: 220: 216: 212: 208: 204: 200: 196: 192: 188: 182: 175: 131: 107:vector space 90: 76: 71: 67: 64:projectivity 63: 56:collineation 31: 25: 3819:, chapter 6 3817:Berger 2009 3747:, chapter 6 3745:Berger 2009 3661:, chapter 4 3659:Berger 2009 3326:, and with 2927:Over a ring 2846:cross-ratio 2778:Cross-ratio 2728:Cross-ratio 2522:composition 2439:of a field 2372:of a point 2353:of ℓ under 1399:permutation 509:isomorphism 395:composition 248:restriction 125:, see also 83:projections 79:perspective 36:isomorphism 4172:Categories 4162:Homography 4003:Geometry I 3968:References 3783:, pp. 43–4 3703:Artin 1957 3697:, p. 244, 3673:, pp. 43–4 2838:to 0, and 2822:that maps 2422:See also: 2327:. Setting 2294:eigenvalue 2286:eigenspace 2282:+1) matrix 2215:homologies 2163:(that is, 2146:hyperplane 1471:vertices. 1239:hyperplane 557:such that 497:homography 391:homography 382:below and 91:homography 50:that maps 32:homography 4076:, Dover, 3987:, Dover, 3757:Yale 1968 3733:Baer 2005 3721:Baer 2005 3701:, p. 50, 3699:Baer 2005 3695:Yale 1968 3595:), where 3251:− 3222:∼ 3119:↦ 2672:PGL(2, 4) 2668:PGL(2, 7) 1350:≠ 1341:− 1292:↦ 1182:⋯ 1100:⋯ 1025:⋮ 983:⋯ 901:⋯ 759:⋯ 706:⋮ 667:⋯ 527:bijection 267:bijection 95:Euclidean 48:bijection 4050:(1979), 3807:, p. 129 3759:, p. 224 3685:, p. 138 3635:See also 3620:= 2 cos( 3419:periodic 3306:integers 2937:Suppose 2633:+ 1) × ( 2596:, where 2520:and the 2345:through 2211:Elations 1949:mapping 1763:+ ... + 1739:), ..., 1687:+ ... + 1663:), ..., 1613:+ ... + 1589:), ..., 1526: : 1504:, where 516: : 491:) and P( 4125:0169108 4108:(1964) 3933:⁠ 3909:⁠ 3795:, p. 30 3771:, p. 96 3723:, p. 76 3705:, p. 88 3641:W-curve 3342:is the 3316:PSL(2, 2949:is its 2916:, then 2736:Use of 2612:of the 2608:is the 2536:space. 2451:to all 2390:, then 2332:= ℓ ∩ ℓ 2278:+1) × ( 1821:, ..., 1650:, then 1636:, ..., 1562:, ..., 1456:simplex 1452:simplex 582:+1) × ( 533:) to P( 529:from P( 503:) to P( 457:, ..., 418:over a 4141:  4118:Oxford 4080:  4062:  4028:  4009:  3991:  3607:, the 3574:> 2 3334:. The 3280:  3204:  3154:  3064:  2616:, and 2426:, and 2361:with ℓ 2191:center 1886:has a 1521:, and 588:matrix 344:, and 246:, the 70:, and 34:is an 3942:9:104 3647:Notes 3609:trace 3605:) = 1 3432:(the 3101:is a 3097:When 2967:with 2941:is a 2888:∪ {∞} 2820:∪ {∞} 2764:As a 2706:+ 1, 2691:+ 1, 2646:is a 2642:When 2602:+ 1, 2584:+ 1, 2569:+ 1, 2549:+ 1, 2526:group 2136:from 2116:onto 1919:tuple 1510:is a 1263:field 596:up to 420:field 271:field 134:field 111:field 52:lines 4139:ISBN 4078:ISBN 4060:ISBN 4026:ISBN 4007:ISBN 3989:ISBN 2945:and 2943:ring 2896:has 2866:and 2797:and 2702:PΓL( 2687:PGL( 2656:PGL( 2637:+ 1) 2588:) / 2565:PGL( 2545:PGL( 2462:The 2265:and 2249:and 2172:) = 2153:axis 2104:, a 2066:, DD 2062:, CC 2058:, BB 1876:) = 1841:and 1487:Let 545:and 305:and 289:, a 281:and 140:and 97:and 81:and 30:, a 3958:in 3936:", 3611:is 3589:hπi 3585:= 1 3567:= 0 3417:is 3346:of 3311:is 2883:of 2828:to 2761:2. 2753:1. 2740:in 2650:GF( 2598:GL( 2580:GL( 2325:(ℓ) 2269:.) 2193:of 2181:in 2155:of 2140:to 2108:of 2102:≥ 2 2034:, D 2030:, C 2026:, B 1752:), 1676:), 1602:), 1572:of 1519:+ 1 1484:. 1469:+ 1 1448:+ 1 1441:+ 2 1426:or 1375:or 814:to 586:+1) 553:of 468:of 438:+ 1 386:.) 352:to 340:to 332:If 318:+ 1 297:to 250:to 168:, D 164:, C 160:, B 85:in 38:of 26:In 4174:: 4122:MR 4120:, 4116:, 4058:, 4054:, 3954:, 3927:+ 3925:cx 3915:+ 3913:ax 3622:hπ 3616:+ 3601:, 3583:bc 3581:− 3579:ad 3563:+ 3350:. 2923:. 2918:= 2910:, 2906:, 2860:, 2854:, 2832:, 2791:, 2724:. 2660:, 2639:. 2459:. 2410:. 2407:OB 2405:∩ 2400:SA 2398:= 2385:∩ 2383:AB 2381:= 2359:OA 2321:= 2315:, 2010:. 1859:. 1772:)) 1723:. 1696:)) 1622:)) 1420:A 1406:. 1379:. 567:. 564:af 562:= 520:→ 410:P( 406:A 361:⋅ 258:. 235:. 205:OA 74:. 66:, 4145:. 4127:. 3929:d 3921:/ 3917:b 3893:, 3888:) 3882:d 3877:c 3870:b 3865:a 3859:( 3630:. 3628:) 3626:m 3624:/ 3618:d 3614:a 3603:m 3599:h 3597:( 3593:m 3591:/ 3572:n 3565:d 3561:a 3535:. 3530:) 3524:1 3519:0 3512:0 3507:1 3501:( 3496:= 3491:) 3485:1 3480:0 3473:n 3468:1 3462:( 3457:= 3452:n 3448:h 3436:n 3430:Z 3427:n 3425:/ 3423:Z 3403:) 3397:1 3392:0 3385:1 3380:1 3374:( 3369:= 3366:h 3340:A 3320:) 3318:Z 3309:Z 3289:. 3286:] 3283:1 3277:, 3274:) 3271:b 3268:+ 3265:a 3262:z 3259:( 3254:1 3247:) 3243:d 3240:+ 3237:c 3234:z 3231:( 3228:[ 3225:U 3219:] 3216:d 3213:+ 3210:c 3207:z 3201:, 3198:b 3195:+ 3192:a 3189:z 3186:[ 3183:U 3157:, 3148:d 3145:+ 3142:c 3139:z 3134:b 3131:+ 3128:a 3125:z 3116:z 3099:A 3082:. 3079:] 3076:d 3073:+ 3070:c 3067:z 3061:, 3058:b 3055:+ 3052:a 3049:z 3046:[ 3043:U 3040:= 3035:) 3029:d 3024:b 3017:c 3012:a 3006:( 3001:] 2998:1 2995:, 2992:z 2989:[ 2986:U 2973:A 2964:U 2959:A 2955:A 2947:U 2939:A 2920:k 2914:) 2912:c 2908:b 2904:a 2902:( 2893:d 2886:F 2881:) 2879:d 2877:( 2875:h 2869:d 2863:c 2857:b 2851:a 2841:c 2835:b 2830:∞ 2825:a 2818:F 2812:h 2806:F 2800:c 2794:b 2788:a 2714:n 2710:) 2708:F 2704:n 2695:) 2693:F 2689:n 2680:5 2678:A 2664:) 2662:q 2658:n 2652:q 2644:F 2635:n 2631:n 2629:( 2625:F 2621:I 2618:F 2606:) 2604:F 2600:n 2593:I 2590:F 2586:F 2582:n 2573:) 2571:F 2567:n 2561:F 2557:n 2553:) 2551:F 2547:n 2487:P 2483:P 2476:P 2472:P 2449:σ 2445:F 2441:F 2437:σ 2402:′ 2395:′ 2393:B 2387:M 2379:S 2374:B 2369:′ 2367:B 2363:′ 2355:α 2351:A 2347:R 2343:M 2339:α 2334:′ 2330:R 2323:α 2319:′ 2317:ℓ 2313:α 2309:O 2305:α 2290:n 2280:n 2276:n 2274:( 2267:Q 2263:P 2259:P 2257:( 2255:α 2251:Q 2247:O 2243:Q 2239:Q 2237:( 2235:α 2231:O 2227:P 2223:P 2221:( 2219:α 2207:α 2203:O 2199:α 2195:α 2187:O 2183:H 2179:X 2174:X 2170:X 2168:( 2166:α 2161:α 2157:α 2149:H 2142:P 2138:P 2134:α 2118:P 2114:P 2110:P 2100:n 2095:P 2076:′ 2072:′ 2068:′ 2064:′ 2060:′ 2056:′ 2052:′ 2050:D 2048:′ 2046:C 2044:′ 2042:B 2040:′ 2036:′ 2032:′ 2028:′ 2024:′ 2008:) 2006:K 2004:( 2001:n 1997:P 1992:) 1990:a 1988:( 1986:h 1980:F 1974:a 1969:) 1967:K 1965:( 1962:n 1958:P 1952:F 1946:h 1940:F 1935:) 1933:V 1931:( 1929:P 1923:v 1915:) 1913:v 1911:( 1909:p 1899:K 1893:p 1884:) 1882:K 1880:( 1878:P 1874:K 1872:( 1869:n 1865:P 1857:K 1853:v 1851:( 1849:p 1844:v 1838:i 1834:e 1830:) 1827:n 1823:e 1819:0 1816:e 1814:( 1809:v 1804:) 1802:v 1800:( 1798:p 1793:) 1791:v 1789:( 1787:p 1769:n 1765:e 1761:0 1758:e 1756:( 1754:p 1749:n 1745:e 1743:( 1741:p 1737:0 1734:e 1732:( 1730:p 1728:( 1707:) 1705:V 1703:( 1701:P 1693:n 1689:e 1685:0 1682:e 1680:( 1678:p 1673:n 1669:e 1667:( 1665:p 1661:0 1658:e 1656:( 1654:p 1652:( 1648:V 1642:n 1638:e 1634:0 1631:e 1626:K 1619:n 1615:e 1611:0 1608:e 1606:( 1604:p 1599:n 1595:e 1593:( 1591:p 1587:0 1584:e 1582:( 1580:p 1578:( 1574:V 1568:n 1564:e 1560:0 1557:e 1552:) 1550:V 1548:( 1546:P 1538:) 1536:V 1534:( 1532:P 1528:V 1524:p 1517:n 1512:K 1507:V 1501:n 1496:) 1494:V 1492:( 1490:P 1477:K 1467:n 1461:n 1446:n 1439:n 1433:n 1356:, 1353:0 1347:c 1344:b 1338:d 1335:a 1327:, 1321:d 1318:+ 1315:z 1312:c 1307:b 1304:+ 1301:z 1298:a 1289:z 1270:K 1266:K 1209:n 1205:x 1199:n 1196:, 1193:0 1189:a 1185:+ 1179:+ 1174:1 1170:x 1164:1 1161:, 1158:0 1154:a 1150:+ 1145:0 1142:, 1139:0 1135:a 1127:n 1123:x 1117:n 1114:, 1111:n 1107:a 1103:+ 1097:+ 1092:1 1088:x 1082:1 1079:, 1076:n 1072:a 1068:+ 1063:0 1060:, 1057:n 1053:a 1046:= 1037:n 1033:y 1010:n 1006:x 1000:n 997:, 994:0 990:a 986:+ 980:+ 975:1 971:x 965:1 962:, 959:0 955:a 951:+ 946:0 943:, 940:0 936:a 928:n 924:x 918:n 915:, 912:1 908:a 904:+ 898:+ 893:1 889:x 883:1 880:, 877:1 873:a 869:+ 864:0 861:, 858:1 854:a 847:= 838:1 834:y 791:. 786:n 782:x 776:n 773:, 770:n 766:a 762:+ 756:+ 751:0 747:x 741:0 738:, 735:n 731:a 727:= 718:n 714:y 694:n 690:x 684:n 681:, 678:0 674:a 670:+ 664:+ 659:0 655:x 649:0 646:, 643:0 639:a 635:= 626:0 622:y 604:φ 600:K 584:n 580:n 578:( 572:φ 560:g 555:K 551:a 547:g 543:f 539:f 535:W 531:V 522:W 518:V 514:f 505:W 501:V 493:W 489:V 478:V 474:V 470:K 466:) 463:n 459:x 455:0 452:x 450:( 446:V 442:V 436:n 431:V 427:K 423:K 416:n 412:V 376:P 368:P 363:f 359:g 354:P 350:Q 346:g 342:Q 338:P 334:f 328:. 326:Q 322:P 316:n 311:R 307:Q 303:P 299:Q 295:P 287:n 283:Q 279:P 252:Q 244:O 240:Q 233:O 221:P 217:O 213:A 209:P 201:A 197:O 193:P 189:O 170:′ 166:′ 162:′ 158:′ 23:.

Index

Homography (disambiguation)
projective geometry
isomorphism
projective spaces
vector spaces
bijection
lines
collineation
fundamental theorem of projective geometry
perspective
projections
Euclidean geometry
Euclidean
affine spaces
points at infinity
vector space
field
projective coordinates
linear algebra
incidence geometry
synthetic geometry
field
Pappus's hexagon theorem
Desargues's theorem

visual perspective
central projection
projective space
points at infinity
restriction

Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.