[gdal-dev] Vector VRT with OGRVRTUnionLayer
Jon Morris
Jon.Morris at jbarisk.com
Wed May 7 01:07:17 PDT 2025
Awesome! Thanks Jukka, that has fixed it. I didn't know wkbUnknown could also be used as a wildcard, but with that tag I don't need to set geometry fields, GDAL manages to find everything and make it appear as if everything is in one layer.
Jon
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-----Original Message-----
From: Rahkonen Jukka <jukka.rahkonen at maanmittauslaitos.fi>
Sent: 06 May 2025 21:36
To: gdal-dev at lists.osgeo.org; Jon Morris <Jon.Morris at jbarisk.com>
Subject: Re: Vector VRT with OGRVRTUnionLayer
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Hi,
Partial answer based on editing the example https://gdal.org/en/stable/drivers/vector/vrt.html#example-union-layer
Sources: polygon shapefile and point shapefile
Output: one layer with unknown/any geometry type
unionlayer.vrt
========
<OGRVRTDataSource>
<OGRVRTUnionLayer name="unionLayer">
<OGRVRTLayer name="poly">
<SrcDataSource>poly.shp</SrcDataSource>
<GeometryType>wkbUnknown</GeometryType>
</OGRVRTLayer>
<OGRVRTLayer name="point">
<SrcDataSource>point.shp</SrcDataSource>
<GeometryType>wkbUnknown</GeometryType>
</OGRVRTLayer>
</OGRVRTUnionLayer>
</OGRVRTDataSource>
ogrinfo unionlayer.vrt -al
INFO: Open of `unionlayer.vrt'
using driver `OGR_VRT' successful.
Layer name: unionLayer
Geometry: Unknown (any)
Feature Count: 2
Extent: (258.000000, 176.000000) - (507.000000, 345.000000) Layer SRS WKT:
(unknown)
OGRFeature(unionLayer):0
POLYGON ((365 311,507 281,332 176,258 237,365 311))
OGRFeature(unionLayer):1
POINT (282 345)
-Jukka Rahkonen-
________________________________________
Lähettäjä: gdal-dev käyttäjän Jon Morris via gdal-dev puolesta
Lähetetty: Tiistai 6. toukokuuta 2025 19.35
Vastaanottaja: gdal-dev at lists.osgeo.org
Aihe: [gdal-dev] Vector VRT with OGRVRTUnionLayer
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.vrtINFO: Open of `test.vrt' using driver `OGR_VRT' successful. Layer name: mergedGeometry (): PolygonGeometry (SHAPE): Multi PolygonFeature Count: 15Extent (): (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: 1,2SRS 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: 2,1Geometry Column 1 =Geometry Column 2 = SHAPEInput 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_LENGTHSHAPE_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 MorrisSoftware Developer-- e: Jon.Morris at jbarisk.comd:+44 (0)1756 587229t: +44 (0)1756 799919www.jbarisk.com[X][X][X][X] All JBA Risk Management's email messages contain confidential information and are intended only for the individual(s) named. If you are not the named addressee you should not disseminate, distribute or copy this e-mail.Please notify the sender immediately by email if you have received this email by mistake and delete this email from your system. JBA Risk Management Limited is registered in England, company number 07732946, 1 Broughton Park, Old Lane North, Broughton, Skipton, North Yorkshire, BD23 3FD, England.
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