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299:'s interior connecting "in an alternated pace: skipping 1 of every 2 vertex", that means => to 7 of the vertex opposite to it, but without routing any line to connect that vertex to the other 8 intermixed vertex (keep in mind: 7+8+itself=16 vertex). The remaining 9 rhumblines (to complete the 16 winds) are projected from each vertex towards the exterior of the hexadecagon, although in some portolans those 9 lines do not appear.
310:); the eight intermediate directions (half-winds) are drawn in green; and in the case of a 32 winds rose, the sixteen remaining (quarter-winds) are drawn in red. The intersection of this set of "rhumblines" determine on the portolans a varied pattern of symmetrical squares, parallelograms, trapezoids and triangles.
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located at various points on the map (or mapamundi). These better called "windrose lines" are generated "by observation and the compass", and are designated today as "lines of course" or "lines of rhumb" ("rhumb lines" in the fourteenth century, traced on portolan's particular projection, though not
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one is able to read the names of those lines which were winds: tramontana, levante, ponente, mezzogiorno, greco, sirocco, and lebegio. When limited to small seas, planispheres approximately follow both rhumb lines and great circles. But on big oceans they do not follow either of them, due to the
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Before modern accurate surveying, there was no method for measuring longitude at sea so maps used to have many distortions, especially in the east west direction. There was also distortion due to the curvature of the Earth's surface. The multitude of compass roses with straight lines extending
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closest to the ship's position, obtaining on it the theoretical course to be followed when sailing towards the destination. This theoretical course may have to be modified (as many times as needed) when tacking if the wind is right ahead of you, or to correct the effects of
120:, since they are not true rhumb lines by the modern definition. A rhumb line in the modern sense is only straight on a chart drawn with the Mercator projection, but not on charts from the 13th–16th centuries. Older windrose lines were a close approximation on charts of the
135:
The grid can be easily spotted (as parchment is quite translucent) by observing a chart from its rear face, with a light source illuminating the other side. The hole in the center of the circle, origin of the whole network, is also clearly visible from the rear.
246:), since a loxodrome gives an accurate course only when the chart is drawn on a suitable projection. Cartometric investigation has revealed that no projection was used in the early charts, for which we therefore retain the name 'portolan'.
635:
Julio Rey Pastor y
Ernesto Garcia Camarero. La cartografia mallorquina. - Madrid: Dep. de historia y filosofia de la ciencia "Inst. Luis Vives", Consejo sup. de investigaciones cientificas 1960. XV, 207 S.
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lines trying to let the 16 vertex in visible places, as shown in
Vescomte's portolan picture with its rhumbline network drawing a 16 vertex regular polygon (hexadecagon) that is perfectly centered on the
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chart in which it is visible how he started by drawing first the rhumbline grid. Some authors call it "winds network" instead of using the term "rhumbline network" or "network of rhumblines".
116:) has been redefined to mean a mathematically precise curve of constant bearing on the Earth's surface. To avoid confusion, the lines on earlier sailing charts can be unambiguously called
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outwards across the map derived from how the maps were then made by compiling empirical observations from navigators who attempted to follow a constant bearing at sea.
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sometimes contained two hexadecagons and has the two opposite corners matching what is called the "portolan diaphragm " (axis of the
Mediterranean .. or parallel of
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Pujades in his book "Les cartes portolanes" has a chapter with all known theories and, with the aim to clarify the controversial arguments, he shows an image of
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that use the double-hexadecagon rhumbline networks but they can not be considered portolan charts since they do not have any ports indicated on them.
372:), the cartographer used to draw two hexadecagons with the two opposite corners superimposed in the center of the vellum. There are plenty of
333:(or two linked by a vertex) with a network of 16 lines per vertex (with the different colors mentioned above: black, green and red).
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226:, for cartometric investigation has revealed that no projection was used in portolans, and those straight lines could be
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639:. Department de historia y filosofia de la ciencia "Inst. Luis Vives", Consejo sup. de investigaciones cientificas.
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the course to follow from a point of origin to a point of destination, one should transfer — using a
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To understand that those lines should be better called "windrose lines", one has to know that
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582:"Portolan charts from the late thirteenth century to 1500 – Additions, Corrections, Updates"
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imprecision of the map making of that time, corresponding more or less accurately to
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for the eight main directions (or winds) are drawn with black ink (or sometimes
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Rhumb line construction scheme with two hexadecagon in the
Texeira planisphere
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Rhumb line construction scheme with two hexadecagon in the
Cantino planisphere
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The word ("Rhumbline") is wrongly applied to the sea-charts of this period (
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share these characteristic "windrose networks", which emanate from
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Les cartes portolanes: la representaciĂł medieval d'una mar solcada
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In large planispheres, especially those containing the oceans (
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The process for a vellum chart creation used to be as follows:
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of good size, or several pieces of vellum glued together.
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only if the chart was drawn on a suitable projection.
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632:Ernesto GarcĂa Camarero; Julio Rey Pastor (1960).
608:CartografĂa marĂtima hispana: la imagen de AmĂ©rica
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279:is divided into sixteen equal parts defining a
27:Navigational aid drawn on early portolan charts
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124:and surrounding areas, but the rhumb lines on
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355:Finally they labeled and decorated the whole
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140:Use of windrose lines on a rhumbline network
605:MarĂa Luisa MartĂn-Merás (1 January 1993).
413:Double hexadecagon in Texeira's planisphere
400:Double hexadecagon in Cantino's planisphere
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295:, 7 rhumblines are projected towards the
530:. Transaction Publishers. pp. 65–.
498:. Transaction Publishers. pp. 65–.
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661:. Institut CartogrĂ fic de Catalunya.
364:Planispheres with double hexadecagon
45:Windrose network -16 vertex on each
655:Ramon J.Pujades i Bataller (2007).
336:They copied on top of the grid the
175:Rhumblines vis-Ă -vis windrose lines
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287:", placed in the 16 vertex of an
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222:are characterized by the lack of
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392:and deviating greatly in the
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458:Majorcan cartographic school
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314:Vellum map creation process
260:Portolan by Petrus Vescomte
203:to be confused with modern
96:Since the invention of the
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443:La CartografĂa Mallorquina
388:only in the Mediterranean
329:They drew a well-centered
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554:P. D. A. Harvey (1991).
132:were highly inaccurate.
57:Image of Petrus Vesconte
30:Not to be confused with
359:more or less profusely.
611:. IGME. pp. 30–.
527:History of Cartography
495:History of Cartography
473:Orthodromic navigation
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685:Portolan-Chart-Lines
448:Leonardo's world map
381:Cresques planisphere
130:Teixeira planisphere
690:Medieval Navigation
586:www.maphistory.info
560:. British Library.
524:Leo Bagrow (2010).
492:Leo Bagrow (2010).
344:In the case of the
98:Mercator projection
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394:Texeira planisfere
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144:To calculate on a
87:age of exploration
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668:978-84-9785-414-6
618:978-84-7782-265-3
567:978-0-7123-0232-6
537:978-1-4128-2518-4
505:978-1-4128-2518-4
468:Octant projection
302:The lines of the
128:maps such as the
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91:marine navigation
81:were used in the
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705:Cartography
433:Catalan map
386:rhumb lines
331:hexadecagon
297:hexadecagon
289:hexadecagon
281:hexadecagon
244:Middle Ages
205:rhumb lines
126:small-scale
106:, the term
104: 1600
710:Navigation
699:Categories
591:2020-08-14
480:References
341:parchment.
285:wind roses
268:drawing a
235:Leo Bagrow
228:loxodromes
109:rhumb line
32:Rhumb line
370:World Map
209:meridians
114:loxodrome
77:). These
426:See also
270:portolan
237:states:
169:currents
47:Portolan
379:In the
304:courses
156:on the
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615:
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357:vellum
350:Rhodes
338:coasts
324:vellum
293:vertex
277:circle
165:leeway
663:ISBN
613:ISBN
562:ISBN
532:ISBN
500:ISBN
308:gold
275:The
194:All
112:(or
85:and
75:maps
65:(or
233:As
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211:or
89:in
34:or
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636:8°
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61:A
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Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
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