[gdal-dev] Problem with adding Attributes to a point shapefile

[Even Rouault]

Selon "Henneke, Amanda M" <amanda.m.henneke at boeing.com>:

Amanda,

The fundamental reason is a call ordering problem. You currently do :

FeatureDefn feadefPt = lyrPt.GetLayerDefn();
Feature feaPt = new Feature(feadefPt);
lyrPt.CreateField(flddefLandUse, 0);

which is wrong as you change the feature definition after having instanciated a
feature. When you instanciate a feature, the feature definition must not change
after (arrays are created with the number of fields of the definition, so layer
the SetField() call will try to set an out-of-bound element). So the fix is to
simply move the feature instanciation after the CreateField() call

Best regards,

Even

> Hello-
>
> I'm trying to create a point shapefile of all the first points in the
> polygons (from a poly shapefile) as shown below.  I also want to assign some
> attributes to the different point features.  I am having some issues doing
> this.  I get an error on the "feaPt.SetField("LAND_USE", sLandUse)" line that
> says "AccessViolationException was unhandled Attempted to read or write
> protected memory.  This is often an indication that other memory is corrupt".
>
> If I take the attribute stuff out it runs fine and creates the shapefile.
> I've done attribute adding before and this way has always worked for me, any
> ideas what I'm doing wrong???
>
>       public void BuildShapefile(string sPolyShapeFile)
>       {
>          Ogr.RegisterAll();
>
>          // Get driver for the shapefiles
>          Driver drvShpFile = Ogr.GetDriverByName("ESRI Shapefile");
>
>          // Create a Spatial Reference
>          OSGeo.OSR.SpatialReference srGeo = new
> OSGeo.OSR.SpatialReference("");
>          srGeo.SetGeogCS("Geographic Coordinate System",
> OSGeo.OSR.Osr.SRS_DN_WGS84, OSGeo.OSR.Osr.SRS_DN_WGS84,
> OSGeo.OSR.Osr.SRS_WGS84_SEMIMAJOR, OSGeo.OSR.Osr.SRS_WGS84_INVFLATTENING,
> "Greenwich", 0.0, "degree", 0.0174532925199433);
>
>          // Create a datasource for the polygon file and for the new point
> file
>          DataSource dsPolyShpFile = Ogr.Open(sPolyShapeFile, 0);
>          DataSource dsPtShpFile =
> drvShpFile.CreateDataSource("D:\\Vector\\Output", new string[] { });
>
>          // Create layers for the polygon file and the point file
>          Layer lyrPoly = dsPolyShpFile.GetLayerByIndex(0);
>          Layer lyrPt = dsPtShpFile.CreateLayer("Junk", srGeo,
> wkbGeometryType.wkbPoint, new string[] { });
>
>          // Create Field Definition, Feature Definition and Features to
> enable us writing attributes to the new shapefile
>
>          FeatureDefn feadefPt = lyrPt.GetLayerDefn();
>
>          Feature feaPt = new Feature(feadefPt);
>          Feature feaPoly;
>
>          FieldDefn flddefLandUse = new FieldDefn("LAND_USE",
> FieldType.OFTString);
>
>          flddefLandUse.SetWidth(100);
>
>          //// Create an attribute field
>          lyrPt.CreateField(flddefLandUse, 0);
>
>          flddefLandUse.Dispose();
>
>          // Create the Geometry for the new point file
>          Geometry geoPoint = new Geometry(wkbGeometryType.wkbPoint);
>
>          Geometry geoPoly = new Geometry(wkbGeometryType.wkbPolygon);
>          Geometry geoPolyRing = new Geometry(wkbGeometryType.wkbLinearRing);
>
>          int iFeaCount = lyrPoly.GetFeatureCount(1);
>
>          // Loop through the poly file to get the points
>          for (int iFea = 0; iFea < iFeaCount; iFea++)
>          {
>             feaPoly = lyrPoly.GetFeature(iFea);
>             string sLandUse = feaPoly.GetFieldAsString("PGLANDUSE");
>             geoPoly = feaPoly.GetGeometryRef();
>             geoPolyRing = geoPoly.GetGeometryRef(0);
>
>             // Add a point
>             geoPoint.AddPoint(geoPolyRing.GetX(0), geoPolyRing.GetY(0), 0.0);
>             feaPt.SetGeometry(geoPoint);
>
>             // Set the attribute
>             feaPt.SetField("LAND_USE", sLandUse);
>
>             lyrPt.CreateFeature(feaPt);
>
>             geoPoint.Empty();
>
>             if (iFea == (iFeaCount - 1))
>                feaPoly.Dispose();
>          }
>          geoPolyRing.Dispose();
>          geoPoly.Dispose();
>          geoPoint.Dispose();
>          feaPt.Dispose();
>          feadefPt.Dispose();
>          lyrPoly.Dispose();
>          lyrPt.Dispose();
>          dsPolyShpFile.Dispose();
>          dsPtShpFile.Dispose();
>          srGeo.Dispose();
>          drvShpFile.Dispose();
>       }
>
> Thanks,
> Amanda M. Henneke
>
>
>
>
> When One tugs at a single thing in Nature, he finds it attached to the rest
> of the world. -John Muir
>   Please consider the environment before printing this e-mail.
>
>
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