Extended Methods on Geometry & Geography Instances

1. Overview

Cinchy CQL supports a number of extended methods on Open Geospatial Consortium (OGC) methods on geometry and geography instances.Please note that all functions that have been denoted with Geography in parentheses are only applicable to OGC methods on geometry instances.

These function are not currently supported in PostgreSQL deployments of the Cinchy platform.

New function translations are actively being worked on by the development team; please check back at a later time.

You can review the full list of in-progress function translations here.

The extended Methods covered in this section are:

IsValidDetailed	MakeValid	Reduce	ShortestLineTo

IsValidDetailed (Geometry)

IsValidDetailed()returns a message that can help to identify problems with a spatial object that is not valid.

Only the first error is returned, when the object is not valid. When the object is valid, a value of 24400 is returned.

Syntax

.IsValidDetailed()  

Return Types

CQL: Text

Remarks

The following table contains possible return values:

Return Value	Description
24400	Valid
24401	Not valid, reason unknown.
24402	Not valid because point {0} is an isolated point, which is not valid in this type of object.
24403	Not valid because some pair of polygon edges overlap.
24404	Not valid because polygon ring {0} intersects itself or some other ring.
24405	Not valid because some polygon ring intersects itself or some other ring.
24406	Not valid because curve {0} degenerates to a point.
24407	Not valid because polygon ring {0} collapses to a line at point {1}.
24408	Not valid because polygon ring {0} is not closed.
24409	Not valid because some portion of polygon ring {0} lies in the interior of a polygon.
24410	Not valid because ring {0} is the first ring in a polygon of which it is not the exterior ring.
24411	Not valid because ring {0} lies outside the exterior ring {1} of its polygon.
24412	Not valid because the interior of a polygon with rings {0} and {1} is not connected.
24413	Not valid because of two overlapping edges in curve {0}.
24414	Not valid because an edge of curve {0} overlaps an edge of curve {1}.
24415	Not valid some polygon has an invalid ring structure.
24416	Not valid because in curve {0} the edge that starts at point {1} is either a line or a degenerate arc with antipodal endpoints

Geometry Example

This example of an invalid spatial object shows how the IsValidDetailed() methods behaves:

DECLARE @p GEOMETRY = 'Polygon((2 2, 4 4, 4 2, 2 4, 2 2))'  
SELECT @p.IsValidDetailed()  
--Returns: 24404: Not valid because polygon ring (1) intersects itself or some other ring.

MakeValid (Geometry)

MakeValid()converts an invalid geometry instance into a geometry instance with a valid Open Geospatial Consortium (OGC) type.

Syntax

.MakeValid ()  

Return Types

CQL: geometry

Remarks

This method may cause a change in the type of the geometry instance, as well as cause the points of a geometry instance to shift slightly.

Geometry Example

This example creates an invalid LineString instance that overlaps itself and uses MakeValid() to make this instance valid:

DECLARE @g geometry;  
SET @g = geometry::STGeomFromText('LINESTRING(0 2, 1 1, 1 0, 1 1, 2 2)', 0);  
SET @g = @g.MakeValid(); 

Reduce (Geometry)

By running the Douglas-Peucker algorithm on the instance with the given tolerance, Reduce()returns an approximation of the given geometry instance produced.

Syntax

.Reduce ( tolerance )  

Arguments

tolerance The tolerance (type float) to input for the approximation algorithm.

Return Types

CQL: geometry

Remarks

This algorithm operates independently on each geometry contained in the instance, for collection types.

Does not modify Pointinstances.

For CircularStringinstances,Reduce() returns a LineString, CircularString, or CompoundCurve instance.

For CompoundCurveinstances,Reduce() returns either a CompoundCurveor LineStringinstance.

On Polygoninstances, the approximation algorithm is applied independently to each ring. If the returned Polygoninstance is not valid, Reduce() will produce a FormatException.

When a circular arc segment is found, the approximation algorithm checks whether the arc can be approximated by its chord within half the given tolerance. Chords meeting this criteria have the circular arc replaced in the calculations by the chord. If a chord doesn't meet this criteria, then the circular arc is kept and the approximation algorithm is applied to the remaining segments.

Geometry Example

This example creates a LineString instance and uses Reduce() to simplify the instance:

DECLARE @g geometry;  
SET @g = geometry::STGeomFromText('LINESTRING(0 0, 0 1, 1 0, 2 1, 3 0, 4 1)', 0);  
SELECT @g.Reduce(.75).ToString();  

ShortestLineTo (Geometry)

ShortestLineTo()returns a LineStringinstance (which is the distance between the two geometry instances) with two points that represent the shortest distance between the two geometry instances.

Syntax

.ShortestLineTo ( other_instance )  

Arguments

other_instance Specifies the second geometry instance that the calling geometry instance is trying to determine the shortest distance to.

Return Types

CQL: geometry

Remarks

Returns a LineStringinstance with endpoints lying on the borders of the two non-intersecting geometry instances being compared.

The length of the LineStringreturned equals the shortest distance between the two geometry instances.

An empty LineStringinstance is returned when the two geometry instances intersect each other.

Geometry Example

This example returns the LineString instance connecting the two points, by finding the shortest distance between a CircularString instance and a LineString instance:

 DECLARE @g1 geometry = 'CIRCULARSTRING(0 0, 1 2.1082, 3 6.3246, 0 7, -3 6.3246, -1 2.1082, 0 0)';  
 DECLARE @g2 geometry = 'LINESTRING(-4 7, 7 10, 3 7)';  
 SELECT @g1.ShortestLineTo(@g2).ToString();