| commit | 31b31299a8fc524f153b945d01c223f70887bc48 | |
| author | Michael Duda <duda@ucar.edu> | |
| Tue, 29 May 2018 18:42:06 +0000 (29 12:42 -0600) | ||
| committer | Michael Duda <duda@ucar.edu> | |
| Tue, 29 May 2018 18:55:59 +0000 (29 12:55 -0600) | ||
| tree | dc565d0b34e27363d5ee6e20c239eadecd4fdd1d | treesnapshot (tar.gz zip) |
| parent | 66c76d94d5bdf147ef7174622ca7e4ef3b8e19a7 | commitdiff |
Fix inaccuracies in latitude computation for polar stereographic projections
The latitude field for polar stereographic projections is computed by taking
the arcsine of a value, and when computed in single precision, this can lead
to visible, discrete steps in the latitude field near +/-90 latitude.
To address this issue, we promote the arguments to the ASIN function to double-
precision. There is apparently no need to promote any other intermediate
terms to double-precision.
A simple test case involves a polar stereographic grid that contains either
pole, and that has a grid distance of <O(100 m).
The latitude field for polar stereographic projections is computed by taking
the arcsine of a value, and when computed in single precision, this can lead
to visible, discrete steps in the latitude field near +/-90 latitude.
To address this issue, we promote the arguments to the ASIN function to double-
precision. There is apparently no need to promote any other intermediate
terms to double-precision.
A simple test case involves a polar stereographic grid that contains either
pole, and that has a grid distance of <O(100 m).
| geogrid/src/module_map_utils.F | diffblobblamehistory |