[gdal-dev] RFC 29: OGR Set Desired Fields

[Martin Dobias]

Hi Tamas

On Thu, Jul 29, 2010 at 9:10 PM, Tamas Szekeres <szekerest at gmail.com> wrote:
> Frank,
>
> If you refer to the OGR_GEOMETRY, OGR_GEOM_WKT, OGR_GEOM_AREA special
> fields, both return a meaningful value (ie. an empty string) when the
> geometry is null. In this regard it would be enough to disable only the
> geometry column of that layer. However since the geometry column is not
> necessarily be added to the field collection at OGRFeatureDefn, disabling
> the geometry column might probably be set at OGRFeatureDefn while the others
> at OGRFieldDefn in my suggested approach:
>
>
> for( int iField = 0; iField < poDefn->GetFieldCount(); iField++ )
> {
>   if (poDefn->GetFieldDefn(iField)->IsIgnored())
>     continue;
>
>   // fetch field
> }
>
> if (!poDefn->IsGeometryIgnored())
>
> {
>   // fetch geometry field
> }

I like this approach - OGRFeatureDefn / OGRFieldDefn look like good
places where to store the flag whether fields or geometry should be
ignored.

Though I'm not sure how to proceed with API for setting what should be
ignored. In your further mail, you suggest
OGRFeatureDefn::EnableGeometryColumn(bool) for geometry (and I presume
something similar for fields, e.g. OGRFieldDefn::SetIgnored(bool) ).
This would however bring some inconsistency, because documentation for
OGRLayer::GetLayerDefn() states that the returned OGRFeatureDefn
shouldn't be modified. But this statement could be probably relaxed so
that changing ignore state of fields/geometry/style will be allowed?

Regards
Martin