Hello all,
I'm trying to write a tool to create vector VRTs and need a bit of
clarification with OGRVRTUnionLayers.
Is it possible to have a union layer when the input layers have different
geometry types? Currently I'm trying Polygon and Multipolygon and I'm not clear
whether this should make a valid VRT or if I need to convert one of my input
layers so the geometry types are the same.
Also, I want to support Shapefile, FileGDB, and PostGIS input layers - the
geometry field names are different for each of these. The example in the doc
shows that fields can be renamed - `<GeometryField name="vrt_geom_field_2"
field="pg_geom_field_2">` but Shapefiles don't appear to have a geometry field
name. Trying `field=""` does not work.
Here's an example VRT that I have created (using GDAL test data
autotest/ogr/data/poly.shp and autotest/ogr/data/filegdb/curves.gdb):
<OGRVRTDataSource>
<Metadata />
<OGRVRTUnionLayer name="merged">
<SourceLayerFieldName>Input layer</SourceLayerFieldName>
<OGRVRTLayer name="poly">
<SrcDataSource relativeToVRT="1">poly.shp</SrcDataSource>
<SrcLayer>poly</SrcLayer>
</OGRVRTLayer>
<OGRVRTLayer name="polygon">
<SrcDataSource relativeToVRT="1">curves.gdb</SrcDataSource>
<SrcLayer>polygon</SrcLayer>
</OGRVRTLayer>
<ExtentXMin>3.339061908000076</ExtentXMin>
<ExtentYMin>38.30604436200008</ExtentYMin>
<ExtentXMax>481645.3125</ExtentXMax>
<ExtentYMax>4765610.5</ExtentYMax>
</OGRVRTUnionLayer>
</OGRVRTDataSource>
Ogrinfo shows separate entries for geometry, extent, wkt, and geometry column.
How can I get the union layer to only show one of each?
$ ogrinfo -al -so test.vrt
INFO: Open of `test.vrt'
using driver `OGR_VRT' successful.
Layer name: merged
Geometry (): Polygon
Geometry (SHAPE): Multi Polygon
Feature Count: 15
Extent (): (3.339062, 38.306044) - (481645.312500, 4765610.500000)
Extent (SHAPE): (3.339062, 38.306044) - (12.092784, 49.244892)
SRS WKT ():
PROJCRS["OSGB36 / British National Grid",
BASEGEOGCRS["OSGB36",
DATUM["Ordnance Survey of Great Britain 1936",
ELLIPSOID["Airy 1830",6377563.396,299.3249646,
LENGTHUNIT["metre",1]]],
PRIMEM["Greenwich",0,
ANGLEUNIT["degree",0.0174532925199433]],
ID["EPSG",4277]],
CONVERSION["British National Grid",
METHOD["Transverse Mercator",
ID["EPSG",9807]],
PARAMETER["Latitude of natural origin",49,
ANGLEUNIT["degree",0.0174532925199433],
ID["EPSG",8801]],
PARAMETER["Longitude of natural origin",-2,
ANGLEUNIT["degree",0.0174532925199433],
ID["EPSG",8802]],
PARAMETER["Scale factor at natural origin",0.9996012717,
SCALEUNIT["unity",1],
ID["EPSG",8805]],
PARAMETER["False easting",400000,
LENGTHUNIT["metre",1],
ID["EPSG",8806]],
PARAMETER["False northing",-100000,
LENGTHUNIT["metre",1],
ID["EPSG",8807]]],
CS[Cartesian,2],
AXIS["(E)",east,
ORDER[1],
LENGTHUNIT["metre",1]],
AXIS["(N)",north,
ORDER[2],
LENGTHUNIT["metre",1]],
USAGE[
SCOPE["Engineering survey, topographic mapping."],
AREA["United Kingdom (UK) - offshore to boundary of UKCS within 49°45'N
to 61°N and 9°W to 2°E; onshore Great Britain (England, Wales and Scotland).
Isle of Man onshore."],
BBOX[49.75,-9,61.01,2.01]],
ID["EPSG",27700]]
Data axis to CRS axis mapping: 1,2
SRS WKT (SHAPE):
GEOGCRS["WGS 84",
ENSEMBLE["World Geodetic System 1984 ensemble",
MEMBER["World Geodetic System 1984 (Transit)"],
MEMBER["World Geodetic System 1984 (G730)"],
MEMBER["World Geodetic System 1984 (G873)"],
MEMBER["World Geodetic System 1984 (G1150)"],
MEMBER["World Geodetic System 1984 (G1674)"],
MEMBER["World Geodetic System 1984 (G1762)"],
MEMBER["World Geodetic System 1984 (G2139)"],
ELLIPSOID["WGS 84",6378137,298.257223563,
LENGTHUNIT["metre",1]],
ENSEMBLEACCURACY[2.0]],
PRIMEM["Greenwich",0,
ANGLEUNIT["degree",0.0174532925199433]],
CS[ellipsoidal,2],
AXIS["geodetic latitude (Lat)",north,
ORDER[1],
ANGLEUNIT["degree",0.0174532925199433]],
AXIS["geodetic longitude (Lon)",east,
ORDER[2],
ANGLEUNIT["degree",0.0174532925199433]],
USAGE[
SCOPE["Horizontal component of 3D system."],
AREA["World."],
BBOX[-90,-180,90,180]],
ID["EPSG",4326]]
Data axis to CRS axis mapping: 2,1
Geometry Column 1 =
Geometry Column 2 = SHAPE
Input layer: String (0.0)
AREA: Real (12.3)
EAS_ID: Integer64 (11.0)
PRFEDEA: String (16.0)
SHAPE_Length: Real (0.0) DEFAULT FILEGEODATABASE_SHAPE_LENGTH
SHAPE_Area: Real (0.0) DEFAULT FILEGEODATABASE_SHAPE_AREA
When I open the VRT programmatically and iterate through the features, FIDs
10-14 (i.e. those from the FGDB layer) have no geometry. Do I need to add
something like `<GeometryField name="SHAPE" />` to each layer so the geometry
fields are found?
Thanks,
Jon
Jon Morris
Software Developer
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