Concave Hull parameters and algorithms

[ghobona]

A comment from the OGC-NA SubCommittee.

The calculation of a concave hull depends on a number of parameters.

For example, Geotools, GEOS library and PostGIS accept various parameters in their concave hull functions.

• https://libgeos.org/doxygen/classgeos_1_1algorithm_1_1hull_1_1ConcaveHull.html
• https://postgis.net/docs/ST_ConcaveHull.html
• https://github.com/locationtech/jts/blob/master/modules/core/src/main/java/org/locationtech/jts/algorithm/hull/ConcaveHull.java

Given that a concave hull depends on various parameters and algorithms chosen, please provide some informative text to highlight this, unless of course, a specific Concave Hull has been specified. In that case, the details of which Concave Hull has been selected should be documented.

Thanks @chris-little for spotting this.

[jabhay]

• Add informative text to describe that concave hull depends on various parameters and algorithms chosen.

[jabhay]

Hey Paul, preferred wording below:

Various implementers use parameters to calculate a concave hull. As such, two implementations may return different results for the same geometry from their concave hull functions. Implementers should make clear any default values used to calculate a concave hull in their documentation.

[chris-little]

...different results from their concave hull functions for the same geometry. would be my preference. ;-)

[jabhay]

Thanks @chris-little , let's go with that @paulc-dstl

[paulc-dstl]

Ok @jabhay will do! I spoke to @chris-little this morning (unaware of the chat on here) and we are all in agreement. So I'll make those changes asap and job done.

[jabhay]

Changes made, and PR ready for approval