Hi, >From the MapServer side, did you try a runtime substitution parameter in the >VRT file? There is a chance it loads the file and does the replacement >afterwards, although it probably just sends on the filename to GDAL.
The FILTER is indeed processed in MapServer. Does the PROCESSING 'NATIVE_FILTER=id=234' approach work? Depending on how many unique values you have, you could generate multiple VRTs and use runtime substitution to load the correct one. Seth -- mastodon: @geographika@mastodon.social On Tue, Jul 29, 2025, at 12:18 AM, Peter Schmitt via gdal-dev wrote: > Hi, > > I have two GDAL questions that are Mapserver adjacent (or perhaps > vice-versa?). > > 1. Does OGRVRTDataSource allow Python code similar to raster VRT Python > Pixel Functions? > 2. Is there a reasonable way to pass custom arguments to a VRT? > > > I have a VRT that executes some SQL: > > <!-- file.vrt --> > <OGRVRTDataSource> > <OGRVRTLayer name="0"> > <SrcDataSource>PG:host=db user=me dbname=datastore > password=abc</SrcDataSource> > <SrcSQL> > SELECT some_table.location, some_table.id, some_table.geom FROM > some_table > </SrcSQL> > </OGRVRTLayer> > </OGRVRTDataSource> > > Is there a reasonable way to pass some argument to filter the VRT? For > example, a condition like `WHERE some_table.id = 123`. Imagine the query has > a very large number of records. I dont want to process the filter "client > side": Ideally the condition gets executed in SQL before OGR gets any > results. I am aware of ogr2ogr's -sql statement > https://gdal.org/en/stable/programs/ogr2ogr.html#cmdoption-ogr2ogr-sql > > Ultimately this will happen via MapServer, which is referencing the VRT > layer. I would like the client to pass a QUERYSTRING argument `foo_id=123` > to perform a filter on the data in the VRT. Usually I do this via MapServer > Runtime substitution. This works if I embed the contents of file.vrt > directly in my Mapfile > > LAYER > NAME my_layer > TYPE POLYGON > EXTENT -180 -90 180 90 > PROJECTION > "init=epsg:4326" > END > CONNECTIONTYPE OGR > TILEITEM 'location' > TILEINDEX "<OGRVRTDataSource>...WHERE some_table.id = > %foo_id%</SrcSQL></OGRVRTLayer></OGRVRTDataSource>" > > VALIDATION > 'foo_id' "^[0-9]+$" > 'default_foo_id' "-1" > END > END > > However, my actual OGRVRTDataSource file is large. If I inline a large VRT > Mapserver complains "msBuildPath(): Unable to access file. Path is too long. > Check server logs.". I could use a Mapserver FILTER > https://mapserver.org/mapfile/layer.html#filter, but I think that occurs > AFTER the VRT is evaluated. . . so if there are millions of rows, that data > gets filtered by the client (Mapserver) and not by SQL, so there's a lot of > data moving around and very slow performance. > > Thanks! > Pete > _______________________________________________ > gdal-dev mailing list > gdal-dev@lists.osgeo.org > https://lists.osgeo.org/mailman/listinfo/gdal-dev >
_______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/gdal-dev
