Snyder equal-area projection: Difference between revisions
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{{Short description|Equal-area polyhedral map projection}} |
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'''Snyder equal-area projection''' is used in the ''[[Geodesic grid|ISEA]] (Icosahedral Snyder Equal Area) [[discrete global grid]]s''. |
'''Snyder equal-area projection''' is a [[polyhedral map projection]] used in the ''[[Geodesic grid|ISEA]] (Icosahedral Snyder Equal Area) [[discrete global grid]]s''. It is named for John P. Snyder, who developed the projection in the 1990s.<ref name="snyder92"> |
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It is a modified [[Lambert azimuthal equal-area projection]], most often applied to a [[polyhedral globe]] consisting of an [[icosahedron]].<ref name="projOrg1"> |
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== external links == |
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{{cite web |url=https://proj.org/operations/projections/isea.html |title=Icosahedral Snyder Equal Area |author=<!--Not stated--> |date=2004-04-04 |orig-date=n.d. |website=[[PROJ]] |publisher=Proj Contributors |access-date=2024-04-09}} |
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</ref><ref name="Carr97"> |
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* https://www.researchgate.net/publication/246557072_ISEA_discrete_global_grids |
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{{cite journal |last1=Carr |first1=D. |last2=Kahn |first2=R. |last3=Sahr |first3=K. |last4=Olsen |first4=T. |date=1997 |title=ISEA Discrete Global Grids |journal=Statistical Computing and Statistical Graphics Newsletter |volume=8 |issue=2/3 |pages=31-39 |url=https://www.researchgate.net/publication/246557072_ISEA_discrete_global_grids |access-date=2024-04-09}} |
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</ref> |
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[[File:DualTiling-TriangHex-fig1.png|thumb|With the [[Dual graph|dual]] [[Euclidean tilings by convex regular polygons|tiling system]] is possible to transform the big triangular faces (gray) into small centered-hexagons (red), and ''vice versa''.]] |
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== Use in the ISEA model == |
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As stated by Carr at al.,<ref name="Carr97"/> page 32: |
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: ''The S in ISEA refers to John P. Snyder. He came out of retirement specifically to address projection problems with the original EMAP grid (see Snyder, 1992). He developed the equal area projection that underlies the gridding system. |
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: ''ISEA grids are simple in concept. Begin with a Snyder Equal Area projection to a regular icosahedron (...) inscribed in a sphere. In each of the 20 equilateral triangle faces of the icosahedron inscribe a hexagon by dividing each triangle edge into thirds (...). Then project the hexagon back onto the sphere using the Inverse Snyder Icosahedral equal area projection. This yields a coarse-resolution equal area grid called the resolution 1 grid. It consists of 20 hexagons on the surface of the sphere and 12 pentagons centered on the 12 vertices of the icosahedron.'' |
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== References == |
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{{Reflist}} |
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{{Map projections}} |
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{{cartography-stub}} |
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[[Category:Equal-area projections]] |
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Latest revision as of 01:25, 11 April 2024
Snyder equal-area projection is a polyhedral map projection used in the ISEA (Icosahedral Snyder Equal Area) discrete global grids. It is named for John P. Snyder, who developed the projection in the 1990s.[1]
It is a modified Lambert azimuthal equal-area projection, most often applied to a polyhedral globe consisting of an icosahedron.[2][3]
Use in the ISEA model[edit]
As stated by Carr at al.,[3] page 32:
- The S in ISEA refers to John P. Snyder. He came out of retirement specifically to address projection problems with the original EMAP grid (see Snyder, 1992). He developed the equal area projection that underlies the gridding system.
- ISEA grids are simple in concept. Begin with a Snyder Equal Area projection to a regular icosahedron (...) inscribed in a sphere. In each of the 20 equilateral triangle faces of the icosahedron inscribe a hexagon by dividing each triangle edge into thirds (...). Then project the hexagon back onto the sphere using the Inverse Snyder Icosahedral equal area projection. This yields a coarse-resolution equal area grid called the resolution 1 grid. It consists of 20 hexagons on the surface of the sphere and 12 pentagons centered on the 12 vertices of the icosahedron.
References[edit]
- ^ Snyder, J.P. (1992). "An Equal-Area Map Projection for Polyhedral Globes". Cartographica. 29 (1): 10–21. doi:10.3138/27H7-8K88-4882-1752. (subscription required)
- ^ "Icosahedral Snyder Equal Area". PROJ. Proj Contributors. 2004-04-04 [n.d.] Retrieved 2024-04-09.
- ^ a b Carr, D.; Kahn, R.; Sahr, K.; Olsen, T. (1997). "ISEA Discrete Global Grids". Statistical Computing and Statistical Graphics Newsletter. 8 (2/3): 31–39. Retrieved 2024-04-09.
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