Firstly, many thanks for taking the time to reply, Brooks, and for your
helpful suggestions.
I tried explicitly adding the geom type and projection by modifying the VRT
file as follows:
<OGRVRTDataSource>
<OGRVRTLayer name="AASQLlayer">
<SrcDataSource>MSSQL:server=zangief\SQLEXPRESS;database=Spatial;trusted_conn
ection=yes</SrcDataSource>
<SrcSQL>SELECT TOP 10 geom27700.STAsText() FROM
TGSettlement_Area</SrcSQL>
<LayerSRS>EPSG:27700</LayerSRS>
<GeometryType>wkbPolygon</GeometryType>
</OGRVRTLayer>
</OGRVRTDataSource>
ogrinfo now reports:
INFO: Open of `mssql.ovf'
using driver `VRT' successful.
Layer name: AASQLlayer
Geometry: Polygon
Feature Count: 10
Layer SRS WKT:
PROJCS["OSGB 1936 / British National Grid",
GEOGCS["OSGB 1936",
DATUM["OSGB_1936",
SPHEROID["Airy 1830",6377563.396,299.3249646,
AUTHORITY["EPSG","7001"]],
TOWGS84[446.448,-125.157,542.06,0.15,0.247,0.842,-20.489],
AUTHORITY["EPSG","6277"]],
PRIMEM["Greenwich",0,
AUTHORITY["EPSG","8901"]],
UNIT["degree",0.0174532925199433,
AUTHORITY["EPSG","9122"]],
AUTHORITY["EPSG","4277"]],
UNIT["metre",1,
AUTHORITY["EPSG","9001"]],
PROJECTION["Transverse_Mercator"],
PARAMETER["latitude_of_origin",49],
PARAMETER["central_meridian",-2],
PARAMETER["scale_factor",0.9996012717],
PARAMETER["false_easting",400000],
PARAMETER["false_northing",-100000],
AUTHORITY["EPSG","27700"],
AXIS["Easting",EAST],
AXIS["Northing",NORTH]]
: String (0.0)
However, I still get the same error with mapnik.
I then tried the solution given in the link you provided, by using OGR2OGR
to first import data into SQL Server so as to create the spatial_ref_sys and
geometry_columns tables.
I'm not sure why these tables should be required, but I can see that they
are referenced in the ogrmssqlspatialselectlayer.cpp file.
Unfortunately, creating these didn't help in this case anyway - I'm still
getting the same error in Mapnik. Just to be clear - I'm able to read and
write spatial data to this SQL Server table using OGR2OGR, which is why I
thought it might be mapnik issue (however, I'm certainly no expert with OGR
either!)
Anyway - I'll continue experimenting. And thanks for your help!
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