Geoscience Reference
In-Depth Information
Fig. 3
Complete healing workflow
LinearRing
with less than 4 vertices is either a line or a point feature but not a
valid polygon. In this case the degenerated polygon is deleted. If a polygon
contains 3 different vertices it is healed by the CP_CLOSE healing process.
CP_CLOSE
: The first and the last vertex of a polygon must be same; therefore
the first vertex is copied to the end of the vertex list. If a
LinearRing
contains four
vertices in a sequence {P
1
, P
2
, P
3
, P
4
} where the last point and the first point are
not identical. {P
1
, P
2
, P
3
, P
4
, P
1
} would be the healed vertex list.
CP_DUPPOINT
: In a
LinearRing
only the first vertex is allowed to repeat
at the end of the point sequence. No other duplicates shall occur. In Fig.
4
three
examples are displayed, where the duplicate vertex is marked red. They are healed
in two different ways: one instance of the duplicate vertex P
4
is deleted in the
upper right
LinearRing
. Deleting an instance of a vertex will result in a change of
the shape for the other
LinearRings
. Here loops are searched within the vertex list.
Those are {P
3
, P
4
, P
5
, P
3
}, {P
3
, P
1
, P
2
, P
3
} (upper left) and {P
2
, P
3
, P
4
, P
2
}, {P
2
,
P
1
, P
2
} (below). The
LinearRings
are split according to the loops.
CP_SELFINT
: Two edges are allowed to intersect only at start and end point
of the edge. Any other intersection will considered as an error. Both
LinearRings
in Fig.
5
have self-intersection errors. There are two healing options. One is to
rearrange the point sequence which works fine with simple polygons in certain
cases. The other one is to extract the intersection points, create new vertices with
those and place the new vertices in between each intersecting edge. So the first
polygon would be {P
1
, P
2
, P
x
, P
3
, P
4
, P
x
, P
1
} where P
x
is the new vertex. This
is not a valid polygon but there is no self-intersection error any more. Duplicate
point errors will be detected and healed during the next iteration step.
CP_PLAN
: Planarity errors occur quite frequently, but they are difficult to heal.
All vertices of a polygon must lie within the same plane regarding a user specified
