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Concept of type and subtype

by Joaquin Jose del Cerro Murciano last modified 2010-09-06 16:14
.. include-document:: org.gvsig.fmap.geom/reference-links

Before seeing how to create a new geometry is necessary to understand the type and subtype concept. Depending on the geometric characteristics, a geometry will be of one type or other. Some types defined on gvSIG are:

* *Point:* for geometries of point type.
* *Curve:* for geometries of line type.
* *Surface:* for geometries of polygon type.
* *Arc:* for geometries of arc type.
* etc.

All the types gvSIG supports currently are in TYPES_ in code form. If at any time somebody needs to create a new geometry that don't use any type on the list, he must contact with the gvSIG's team to assign a new code to the type, because it must be unique.

The type only refers to the type of the geomatic object, but it doesn't specify if geometry is on 2 or 3 dimensions, or if it supports M coordinate or not. For that, it's created the subtype concept, to indicate the geometry dimension. The gvSIG's subtypes are in SUBTYPES and it's the same than the types: if somebody wants to add a new subtype must contact with gvSIG's team to provide you a new code. In the next list we show several subtypes supported on gvSIG:

* *GEOM2D:* 2-dimensional geometries.
* *GEOM2DZ:* 2-dimensional geometries and value for coordenate Z.
* *GEOM3D:* 3-dimensional geometries.
* *GEOM2DM:* 2-dimensional geometries and M coordenate.
* *GEOM3DM:* 3-dimensional geometries and M coordenate.

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