Martin Dobias wrote:
Hi Tamas
On Thu, Jul 29, 2010 at 9:10 PM, Tamas Szekeres <[email protected]> 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?
Martin,
I do not agree with applications directly changing the OGRFieldDefn, even
if ultimately the flag is stored here. There needs to be a virtual method
on the OGRLayer (IMHO) so that drivers have an opportunity to hook the
method to do something special when the list of desired fields changes.
I'm disappointed that several new methods will be added to the API, with
distinct methods for geometry, and style. I am always fighting to
minimize the breadth of the API, within reason. Hopefully you can weld
these results into a RFC proposal we can vote on reasonably soon.
Best regards,
--
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up | Frank Warmerdam, [email protected]
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush | Geospatial Programmer for Rent
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