Working with vertex attributes

Each vertex of a geometry, in addition to its x,y coordinates, can optionally have additional attributes, or vertex attributes.

The z-vertex attribute is a double-precision value that can be used to represent heights or depths relative to a vertical coordinate system. The m-vertex attribute, or measure, is a double-precision value that can be used to establish a linear reference system on a geometry (usually a polyline), such as exits along a highway. The ID vertex attribute, or point ID, is a signed integer that can be used as a foreign database key to associate additional information with each vertex such as survey measurements.

The ID attribute is a numeric label but does not serve any computational purpose. Vertex attributes can be added to, or removed from, any geometry at any time and in any combination. For example, a polyline can start with no vertex attributes, have Zs added to it, have IDs added to it, then have its Zs removed.

When a geometry is aware of its vertex attributes, those attributes are persisted as part of the geometry and included in the output of topological operations that involve that geometry. If a geometry is not aware of its attributes, those attributes are ignored when the geometry is persisted, and the attributes do not appear in the output of a topological operation involving that geometry. The attribute awareness of a geometry is controlled by the IZAware, IMAware, or IPointIDAware interface. The attribute values are not actually removed from a geometry if its awareness is disabled.

See the following code example:

IPoint pnt = new PointClass()as IPoint;
pnt.PutCoords(1, 1);
IZAware zAware = pnt as IZAware;
zAware.ZAware = true;
pnt.Z = 11.1;

Dim pnt As IPoint = CType(New PointClass, IPoint)
pnt.PutCoords(1, 1)
Dim zAware As IZAware = CType(pnt, IZAware)
zAware.ZAware = True
pnt.Z = 11.1