PostgreSQL/PostGIS implementation of the discrete isolation. The resulting value can be used for point selection purposes. It needs a single-point geometry and a numerical value. For usage, you need the data in a PostgreSQL database with the PostGIS extension. It works well with around 10,000 points; you have to consider a long execution time with more points. If you have less than 1,000 points, take a look at the free QGIS Plugin.
Here some sample data using peaks. The geometry is just for the illustration shown as Well-known text.
| id | name | elevation | isolation | geom::geometry(Point, 3857) |
|---|---|---|---|---|
| 1 | Cottaer Spitzberg | 391 | POINT (1554915.030049 6603385.479223) | |
| 2 | Mt. Everest | 8848.86 | POINT (9676427.650365 3247440.479570) | |
| 3 | Zugspitze | 2962 | POINT (1222988.989970 6011100.150710) | |
| 4 | Dürrer Berg | 437 | POINT (1553173.319730 6597213.489256) |
The syntax for the function is the follwing:
discrete_isolation(table_name::text, name_of_geometry_column::text, name_of_elevation_column::text,
geometry_of_point::geometry, elevation_of_point::numeric (, max_search_radius::numeric))
All calculations are made within the given spatial reference system; also, the isolation is measured in this system. For best results, project first the data and afterward calculate the isolation. For a better performance create an index on the elevation and geometry column.
For calculating the discrete isolation in our example, run the following query:
UPDATE peaks
SET isolation = discrete_isolation('peaks', 'geom', 'elevation', geom, elevation)
It will fill the isolation column in the sample table called "peaks". If you want to limit the search radius, you can use the following query.
UPDATE peaks
SET isolation = discrete_isolation('peaks', 'geom', 'elevation', geom, elevation, 100000)