Point_in_polygon
Geometric functions point_in_polygon
syntax
- point_in_polygon(point_data_item, polygon_data_item)
definition
point_in_polygon(point_data_item, polygon_data_item) results for each point of the point_data_item in a relation towards the Domain unit of the polygon_data_item in which the point is located.
The resulting Values unit is the domain unit of the polygon_data_item.
If a point is not located in any polygon, the function results in a Null value (the yellow point in the image). If a point is located in multiple polygons, the function results in one of them, and which one is not specified: it is the first one that the function’s spatial index finds, which follows from how that index is built and can differ between versions of GeoDMS. A configuration, and a test, must not depend on which one it is. If you want to choose among overlapping polygons, use the Point_in_ranked_polygon function; with a constant rank, that takes the polygon with the lowest index.
The first one found is kept because it is fast: a search that stops at the first polygon containing the point does not have to look at the rest. Choosing the lowest index instead made this function about 7 times slower on polygons that do not overlap.
Since GeoDMS 20.23.1 the spatial index splits its nodes at another size (#1289), and that changed which of several overlapping polygons is found first: a point in 14 identical polygons (numbered 1 to 14) got polygon 14 where it got polygon 3. A configuration with overlapping polygons can therefore get other results for the points in the overlap after upgrading; a point in one polygon only gets the same result as before.
description
The point_in_polygon function was used in earlier versions of the GeoDMS to rasterize polygon data. Since version 6.025, it is advised to use the Poly2grid function for this purpose.
performance
O(n log p + n * k) where n = number of points, p = number of polygons, and k = average polygon complexity. Builds a spatial index on polygons for efficient lookup. For large-scale rasterization, prefer Poly2grid.
applies to
- a Data item point_data_item with Point Value type
- a data item polygon_data_item with composition type type polygon and Point value type
example
attribute<district> district_rel (ADomain) := point_in_polygon(Adomain/point, district/geometry);
| point | district_rel |
|---|---|
| xy(115135; 401331) | 6 |
| xy(111803; 399476) | 4 |
| xy(114903; 399289) | 1 |
| xy(111353; 401729) | 5 |
| xy(111741; 398696) | null |
ADomain, nr of rows = 5
| District/geometry |
|---|
| {21:xy(113810; 403025),{4 |
| {17:xy(113269; 400990),{4 |
| {19:xy(115099; 403128),{4 |
| {23:xy(113703; 402174),{4 |
| {30:xy(114646; 401531),{4 |
| {13:xy(114546; 402757),{4 |
| {54:xy(113562; 405282),{4 |
domain District, nr of rows = 7