On mercredi 25 septembre 2019 22:47:21 CEST Markus Metz wrote: > Several different methods might be available to reproject from one CRS to > another CRS. PROJ6 can select the most appropriate method if a bounding box > is provided. This means that the selected method depends on the bounding > box and that results of a reprojection can differ depending on the provided > bounding box. > > In GRASS, this bounding box can be obtained from the current region. That > means if the current region changes, the method and thus the results of > coordinate reprojection might change. This effect can not be underestimated. > > With the current pull request #118 the current region is used to help PROJ6 > select the best method, and [r|v].import should work as before. Results can > be different compared to PROJ5 or earlier. > > IMHO, there is no way around that users become more familiar with details > of coordinate reprojection and need to read the output of [r|v].proj > carefully regarding different methods known to PROJ6. > > PROJ6 will not use the best method if any required datum transformation > grid is not available. Users will need to obtain the corresponding grid > themselves, which raises another question: where to put this grid? On > Linux, this would be e.g. /usr/share/proj, but if the user can not write to > /usr/share/proj, the grids need to be saved somewhere in $HOME, and PROJ6 > must look at that place. This problem, i.e. the place where PROJ6 should > look for in $HOME is not yet solved AFAICT (proj-6.2.0).
Applications may decide for an appropriate user directory and set it with proj_context_set_search_paths() (in that case this overrides PROJ_LIB or hardcoded directories, so you have to add in the search paths if this is the desired behaviour) QGIS has code to do exactly that: https://github.com/qgis/QGIS/blob/65359bc7eafbfe967c669d1428eeedb87c5cd2a1/ src/core/qgsapplication.cpp#L312 and https://github.com/qgis/QGIS/blob/d45c3dd4f1e8fe3642d42d84aa978b28dba913aa/ src/core/qgsprojutils.cpp#L258 -- Spatialys - Geospatial professional services http://www.spatialys.com _______________________________________________ grass-dev mailing list grass-dev@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-dev