poly2grid_untiled

syntax

poly2grid_untiled(polygon_data_item, gridunit)

definition

The poly2grid_untiled function results in a Grid Data item with a relation to the Domain unit of the polygon_data_item.

The resulting data item has:

as Domain unit the gridunit argument
as Values unit the Domain unit of the polygon_data_item Argument

description

This function is the same as Poly2grid but writes single-threaded on a single mutable shadow tile that is then split into separate tiles after rendering all polygons. Compared to Poly2grid, this poly2grid_untiled function will:

take longer to calculate (as it doesn’t process tiles in parallel),
use more memory (to store the intermediate mutable shadow tile),
but use less CPU time (as polygon preparation is not repeated for each tile with which their bounding box intersects),
the results are independent of the actual tiling (which is not always true for Poly2grid as the conversion to a tile-local coordinate system might cause tiling-dependent flip-cases).

applies to

data item polygon_data_item with a wpoint, spoint, upoint, ipoint, fpoint or dpoint Value type
Unit gridunit with a wpoint, spoint, upoint, ipoint, fpoint, dpoint value type

conditions

The composition type type of the polygon_data_item needs to be polygon.
The Domain unit of the polygon_data_item must be of value type uint32.

since version

8.7.0

performance

Same complexity as Poly2grid: O(n * log(n) + x) per polygon where n = number of vertices and x = number of pixels. Single-threaded execution uses more wall-clock time but less total CPU time than tiled version. Memory usage is higher due to full shadow tile allocation.

example

attribute<source/district> DistrictGrid (gridunit/gridcel_10m) := 
   poly2grid_untiled(Source/District/border, gridunit/gridcel_10m);