Changeset 8cfb486 in sasmodels for doc/guide/orientation


Ignore:
Timestamp:
Dec 20, 2017 4:16:27 PM (7 years ago)
Author:
Paul Kienzle <pkienzle@…>
Branches:
master, core_shell_microgels, magnetic_model, ticket-1257-vesicle-product, ticket_1156, ticket_1265_superball, ticket_822_more_unit_tests
Children:
5fb0634
Parents:
06ee63c
Message:

update orientation docs

File:
1 edited

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  • doc/guide/orientation/orientation.rst

    r06ee63c r8cfb486  
    128128symmetry. 
    129129 
    130 There are alternative projections. The 
    131 `sinusoidal projection <https://en.wikipedia.org/wiki/Sinusoidal_projection>`_ 
     130Alternative projections were considered. 
     131The `sinusoidal projection <https://en.wikipedia.org/wiki/Sinusoidal_projection>`_ 
    132132works by scaling $\Delta\phi$ as $\Delta\theta$ increases, and dropping those 
    133133points outside $[-180, 180]$. The distortions are a little less for middle 
    134134ranges of $\Delta\theta$, but they are still severe for large $\Delta\theta$ 
    135 and the model is much harder to explain. The 
    136 `Guyou projection <https://en.wikipedia.org/wiki/Guyou_hemisphere-in-a-square_projection>`_ 
     135and the model is much harder to explain. 
     136The `azimuthal equidistance projection <https://en.wikipedia.org/wiki/Azimuthal_equidistant_projection>`_ 
     137also improves on the equirectangular projection by extending the range of 
     138reasonable values for the $\Delta\theta$ range, with $\Delta\phi$ forming a 
     139wedge that cuts to the opposite side of the sphere rather than cutting to the 
     140pole. This projection has the nice property that distance from the center are 
     141preserved, and that $\Delta\theta$ and $\Delta\phi$ act the same. 
     142The `azimuthal equal area projection <https://en.wikipedia.org/wiki/Lambert_azimuthal_equal-area_projection>`_ 
     143is like the azimuthal equidistance projection, but it preserves area instead 
     144of distance. It also has the same behaviour for $\Delta\theta$ and $\Delta\phi$. 
     145The `Guyou projection <https://en.wikipedia.org/wiki/Guyou_hemisphere-in-a-square_projection>`_ 
    137146has an excellent balance with reasonable distortion in both $\Delta\theta$ 
    138147and $\Delta\phi$, as well as preserving small patches. However, it is 
    139 considerably more expensive to implement, and we have not yet computed the 
     148considerably more overhead, and we have not yet derived the formula for the 
    140149distortion correction, measuring the degree of stretch at the point 
    141 $(\Delta\theta, \Delta\phi)$ in the correction. 
     150$(\Delta\theta, \Delta\phi)$ on the map. 
    142151 
    143152.. note:: 
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