Seth,
In Proj4 adding new projections was as simple as adding a new string to the
epsg text tile in the PROJ_LIB directory. With Proj6+ the proj.db Sqlite
database is used. I believe the text files are no longer used at all
+init=foo:bar should still try to use a "foo" text file. And if you have
an "epsg" text file, it will have precedence over proj.db for
+init=epsg:XXXX codes (although I don't recommend this, because proj.db
will be completely ignored for any epsg entry, so you'd better make sure
your text file is complete enough)
(although the GIS Internals proj7/share includes an other.extra file in the
same format - is this also ignored?).
I presume +init=other.extra:XXXX should still work
So to add a new projection would require adding a new record to proj.db.
The docs at https://proj.org/apps/projinfo.html refer to a
`--dump-db-structure` parameter:
New in version 8.1.
Outputs the sequence of SQL statements to create a new empty valid
auxiliary database.
This option can be specified as the only switch of the utility.
If also specifying a CRS object and the --output-id option, the
definition of the object as SQL statements will be appended.
There is also a new environment variable (see Even's comment at [3]) -
PROJ_AUX_DB that allows this to be read by Proj.
- Is this the recommended approach for MapServer users? (Import any new
projections into a new proj_extra.db and setting this as an environment
variable).
The mechanism technically works but it has been reported in
https://github.com/OSGeo/PROJ/issues/2904 that there are at least in
some use cases with significant performance degradation. I'm not
completely sure if it would affect Mapserver use cases though, and the
degradation would only affect the setup of reprojection objects, so it
should likely be OK for FastCGI scenarios where they are cached and thus
an extra cost can be amortized.
- What is the recommended approach for MapServer deployments with PROJ >=6 and
<=9?
Not easy to answer this. To be honest nothing has beaten yet the
simplicity of old PROJ.4 string. If you have not too complex
requirements regarding datum shifts expressed by those and aren't
mapping at a sub-metric level, they are probably good enough for most
use cases. If you want to be able to express geodesy-grade datum
transformations, you'd better setting up proper CRS and transformation
records, either by patching proj.db or using an auxiliary database.
- Is PROJ_AUX_DB a setting that can be added to the MapServer CONFIG file?
Probable not. I assume that currently, it should be set by the HTTP
server itself, before it forks mapserver CGI. In a CONFIG block, this
would only go through CPLSetConfigOption() but PROJ reads through
getenv() or if it was set with proj_context_set_database_path(). I
presume the msSetConfigOption() logic should have a special case similar
to the PROJ_DATA one so that setting PROJ_AUX_DB calls
OSRSetPROJAuxDbPaths() (GDAL >= 3.3)
- Would it be worth adding the PROJ and GDAL versions to the mapserver -v
output as several of these options rely on newer versions of PROJ?
why not
Even
--
http://www.spatialys.com
My software is free, but my time generally not.
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