vendredi 28 décembre 2018

SRS barn raising: 7th report

This is the 7th progress report of the GDAL SRS barn effort.

On the PROJ side, things are consolidating up. Tens of "random" fixes have been pushed due to the GDAL autotest suite triggering a number of interesting cases. The C API has also been enhanced to accommodate for the needs of GDAL and libgeotiff. We also have received feedback from an early adopter (a developer of a pyproj binding based on PROJ master). The major development items have been the move of the WKT 1 syntax validation from GDAL to PROJ, as well as the development of an equivalent WKT 2 syntax validator in PROJ (this task has been useful to uncover a few minor issues in the draft of the future WKT2:2018 standard). A reorganization of the PROJ source tree (with a conversion of most C files to C++ files) has also been done, as a preliminary step, for a pull request to better integrate the new ISO-19111 functionality I developed those last months with the existing C API.

Regarding libgeotiff, a v1.4.3 maintenance version has been released with the fixes of the last two years, before the new works for the integration of PROJ master are done. libgeotiff development has been moved from Subversion to As a preliminary step, continuous integration capability has been added to test compilation under Linux/GCC and Windows/Visual Studo, with a few runtime tests.
A pull request is ready with the integration of PROJ master with libgeotiff. It features:
  • PROJ master / PROJ 6 as a required depedency of libgeotiff
  • Use of the proj.db database to resolve the various coded values, mostly in the GTIFGetDefn() "normalization" function of libgeotiff, instead of using the .csv files previously generated from the EPSG database. Typically an EPSG code identifying a projected CRS is resolved them into its base elements: projection method, projection parameters, base geodetic CRS, etc..
  • Complete removal of those .csv files and associated functionality
This work will be merged once the above mention PROJ pull request that affects naming of the new functions of the C API has been merged and taken into account. This gdalbarn branch of libgeotiff has also been succesfully integrated in the internal libgeotiff copy of the GDAL gdalbarn branch.

Regarding GDAL, a maintenance v2.3.3 and feature v2.4.0 versions have been released for the same reasons as above.
Most methods of the OGRSpatialReference class have now been re-implemented to rely on the PROJ C API to do queries and state changes, which avoids potentially lossy import / export to WKT 1. Similarly to the libgeotiff work, the ImportFromEPSG() functionality now relies on proj.db, and consequently all EPSG or ESRI related .csv files have been removed from the GDAL data directory. I've also drafted a plan regarding on how to be able to take into account WKT 2 by GDAL raster drivers, and proposed changes regarding how to better handle the gap between the axis order as mandated by the CRS authority (for example latitude first, longitude second for geographic CRS in the EPSG dataset) and the actual order of the values in raster metadata or vector geometries. The first part (use of OGRSpatialReference in raster driver) has been implemented in the gdalbarn branch and the second part is in good progress, with the drivers now advertizing their data axis to CRS axis mapping. The ongoing work is to make  OGRCoordinateTransformation use the PROJ API to automatically compute the best transformation pipeline, enabling late-binding capabilities.

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