|
|
@@ -127,17 +127,17 @@ vlibFeatureTypes):
|
|
|
- boundary: the border line to describe an area (2D only);
|
|
|
- centroid: a point within a closed boundary(ies) to describe an area
|
|
|
(2D only);
|
|
|
-- edge: a 3D boundary (not implemented yet)
|
|
|
+- face: a 3D boundary (not implemented yet);
|
|
|
- kernel: a 3D centroid in a volume.
|
|
|
|
|
|
From vector feature types mentioned above are derived:
|
|
|
|
|
|
-- node: endpoint of a line (2D or 3D);
|
|
|
-- area: the topological composition of centroid and boundary(ies) (2D
|
|
|
- only);
|
|
|
+- node: start/endpoints of lines and boundaries (2D or 3D);
|
|
|
+- area: the topological composition of a closed ring of boundary(ies)
|
|
|
+ and optionally a centroid (2D only, 3D coordinates supported but ignored);
|
|
|
- isle: an area within area, not touching the boundaries of the outer
|
|
|
- area (2D only);
|
|
|
-- face: a 3D area (not implemented yet);
|
|
|
+ area (2D only, 3D coordinates supported but ignored);
|
|
|
+- edge: a 3D node connecting faces (not implemented yet)
|
|
|
- volume: a 3D corpus, the topological composition of faces and kernel
|
|
|
(not implemented yet);
|
|
|
- hole: a volume within volume, 3D equivalent to isle within area (not
|
|
|
@@ -145,7 +145,7 @@ From vector feature types mentioned above are derived:
|
|
|
|
|
|
Note that all lines and boundaries can consist of multiple segments.
|
|
|
|
|
|
-Topology also holds information about isles. Isles are located within an area, not
|
|
|
+Area topology also holds information about isles. Isles are located within an area, not
|
|
|
touching the boundaries of the outer area. Isles consist of one or more areas
|
|
|
and are used internally by the vector libraries to maintain correct topology of areas.
|
|
|
|
|
|
@@ -393,7 +393,7 @@ Besides internal library functions there are two main libraries:
|
|
|
For historical reasons, there are two internal libraries:
|
|
|
|
|
|
- diglib (with dig_*() functions), GRASS 3.x/4.x
|
|
|
-- Vlib (with V1_*(), V2_*() and Vect_*() functions), GRASS 4.x/5.x
|
|
|
+- Vlib (with V1_*(), V2_*() and Vect_*() functions), since GRASS 4.x
|
|
|
(except for the 5.7 interim version)
|
|
|
|
|
|
The vector library was introduced in GRASS 4.0 to hide internal vector
|
|
|
@@ -1127,7 +1127,7 @@ In GRASS, whenever an 'inner' ring touches the boundary of an outside
|
|
|
area, even in one point, it is no longer an 'inner' ring (Isle in
|
|
|
GRASS topology), it is simply another area. A, B above can never be
|
|
|
exported from GRASS as polygon A with inner ring B because there are
|
|
|
-only 2 areas A and B and no island.
|
|
|
+only 2 areas A and B and one island formed by A and B together.
|
|
|
|
|
|
|
|
|
\subsubsection vlibTopoExample3 Topology Example 3
|
Markus Metz