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Conformal map projection
The
Guyou hemisphere-in-a-square projection
is a
conformal
map projection
for the hemisphere. It is an oblique aspect of the
Peirce quincuncial projection
.
History
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]
The projection was developed by
Emile Guyou
[
fr
]
of France in 1887.
[1]
[2]
Formal description
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The projection can be computed as an oblique aspect of the Peirce quincuncial projection by rotating the axis 45 degrees. It can also be computed by rotating the coordinates −45 degrees before computing the stereographic projection; this projection is then remapped into a square whose coordinates are then rotated 45 degrees.
[3]
The projection is conformal except for the four corners of each hemisphere's square. Like other conformal polygonal projections, the Guyou is a
Schwarz?Christoffel mapping
.
Properties
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Its properties are very similar to those of the
Peirce quincuncial projection
:
- Each hemisphere is represented as a square, the sphere as a rectangle of aspect ratio 2:1.
- The part where the exaggeration of scale amounts to double that at the centre of each square is only 9% of the area of the sphere, against 13% for the Mercator and 50% for the stereographic
[4]
- The curvature of lines representing great circles is, in every case, very slight, over the greater part of their length.
[4]
- It is conformal everywhere except at the corners of the square that corresponds to each hemisphere, where two meridians change direction abruptly twice each; the Equator is represented by a horizontal line.
- It can be
tessellated
in all directions.
Related projections
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See also
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References
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