Changes between Version 6 and Version 7 of FAQCoordinateSystemsAndProjections


Ignore:
Timestamp:
Dec 12, 2009, 6:18:48 AM (14 years ago)
Author:
Even Rouault
Comment:

Add a section in the FAQ to answer the question : Does GDAL/OGR use the PROJ.4 EPSG init file ?

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  • FAQCoordinateSystemsAndProjections

    v6 v7  
    1515
    1616There is no such thing as an accurate "default" set of datum transformation parameters for a datum. OGR uses (NADCON) by default, which is the most accurate available for North America, but in the general case (worldwide) this is very hard to determine and there normally is no such thing as a default. The transformation that should be used depends on the exact area covered, accuracy required etc. In other words, user beware and do your homework. [http://proj.maptools.org/faq.html 1], [http://casoilresource.lawr.ucdavis.edu/drupal/node/259 2], [http://www.nabble.com/issue-warning-to-user-when-performing-datum-shift-%28OGR%2C-GDAL%29-t2029971.html 3],
     17
     18== Does GDAL/OGR use the PROJ.4 EPSG init file (/usr/share/proj/epsg) ? ==
     19
     20(coming from this [http://lists.osgeo.org/pipermail/gdal-dev/2009-November/022688.html gdal-dev thread])
     21
     22There are special circumstances when the PROJ.4 EPSG init file is
     23consulted (if no definition is found in the pcs/gcs CSV files in the $(GDAL_DATA) directory).
     24But normally GDAL/OGR does not use the PROJ.4 init files at all(contrary to MapServer)
     25
     26PROJ.4 EPSG init file is periodically generated from the GDAL
     27pcs/gcs.csv files and so they do normally match quite exactly for contemporary
     28GDAL and PROJ.4 released versions.
     29
     30And for those who wonder where the GADL pcs/gcs CSV files come from,
     31they can get the full picture described in the
     32[http://svn.osgeo.org/metacrs/geotiff/trunk/libgeotiff/csv/README EPSG tables generation process]