Class CoveragePolygonValidator

java.lang.Object
org.locationtech.jts.coverage.CoveragePolygonValidator

public class CoveragePolygonValidator extends Object
Validates that a polygon forms a valid polygonal coverage with the set of polygons adjacent to it. If the polygon is coverage-valid an empty LineString is returned. Otherwise, the result is a linear geometry containing the target polygon boundary linework causing the invalidity.

A polygon is coverage-valid if:

  1. The polygon interior does not intersect the interior of other polygons.
  2. If the polygon boundary intersects another polygon boundary, the vertices and line segments of the intersection match exactly.

The algorithm detects the following coverage errors:

  1. the polygon is a duplicate of another one
  2. a polygon boundary segment equals an adjacent segment (with same orientation). This determines that the polygons overlap
  3. a polygon boundary segment is collinear and overlaps an adjacent segment but is not equal to it
  4. a polygon boundary segment touches an adjacent segment at a non-vertex point
  5. a polygon boundary segment crosses into an adjacent polygon
  6. a polygon boundary segment is in the interior of an adjacent polygon

If any of these errors is present, the target polygon does not form a valid coverage with the adjacent polygons.

The validity rules do not preclude properly-noded gaps between coverage polygons. However, this class can detect narrow gaps, by specifying a maximum gap width using setGapWidth(double). Note that this will also identify narrow gaps separating disjoint coverage regions, and narrow gores. In some situations it may also produce false positives (i.e. linework identified as part of a gap which is wider than the given width). To fully identify gaps it maybe necessary to use CoverageUnion and analyze the holes in the result to see if they are acceptable.

A polygon may be coverage-valid with respect to a set of surrounding polygons, but the collection as a whole may not form a clean coverage. For example, the target polygon boundary may be fully matched by adjacent boundary segments, but the adjacent set contains polygons which are not coverage-valid relative to other ones in the set. A coverage is valid only if every polygon in the coverage is coverage-valid. Use CoverageValidator to validate an entire set of polygons.

The adjacent set may contain polygons which do not intersect the target polygon. These are effectively ignored during validation (but may decrease performance).

Author:
Martin Davis
See Also:
  • Constructor Details

    • CoveragePolygonValidator

      public CoveragePolygonValidator(Geometry geom, Geometry[] adjGeoms)
      Create a new validator.

      If the gap width is specified, the set of surrounding polygons should include all polygons which are within the gap width distance of the target polygon.

      Parameters:
      geom - the geometry to validate
      adjGeoms - the adjacent polygons in the polygonal coverage
  • Method Details

    • validate

      public static Geometry validate(Geometry targetPolygon, Geometry[] adjPolygons)
      Validates that a polygon is coverage-valid against the surrounding polygons in a polygonal coverage.
      Parameters:
      targetPolygon - the polygon to validate
      adjPolygons - the adjacent polygons
      Returns:
      a linear geometry containing the segments causing invalidity (if any)
    • validate

      public static Geometry validate(Geometry targetPolygon, Geometry[] adjPolygons, double gapWidth)
      Validates that a polygon is coverage-valid against the surrounding polygons in a polygonal coverage, and forms no gaps narrower than a specified width.

      The set of surrounding polygons should include all polygons which are within the gap width distance of the target polygon.

      Parameters:
      targetPolygon - the polygon to validate
      adjPolygons - a collection of the adjacent polygons
      gapWidth - the maximum width of invalid gaps
      Returns:
      a linear geometry containing the segments causing invalidity (if any)
    • setGapWidth

      public void setGapWidth(double gapWidth)
      Sets the maximum gap width, if narrow gaps are to be detected.
      Parameters:
      gapWidth - the maximum width of gaps to detect
    • validate

      public Geometry validate()
      Validates the coverage polygon against the set of adjacent polygons in the coverage.
      Parameters:
      adjGeoms - the surrounding polygons in the coverage
      Returns:
      a linear geometry containing the segments causing invalidity (if any)