GME

Geospatial Modelling Environment

geom.polygonfetch (Calculate Fetch In Polygons)

Determines the longest line that can be position within the bounds of a polygon, crossing no edges

Description

This tool estimates the longest straight line that can be positioned within a polygon, without crossing any edges. It corresponds to the 'fetch' of a lake: the longest stretch of water over which waves can build up as a function of wind action. The calculation is based on evaluating the lines created by connecting all pairs of non-neighbouring vertices and retaining the longest line that does not cross any interior or exterior boundaries of the polygons. This is a brute force algorithm that can take a long time for very complex polygons (e.g. polygons with more than 1000 vertices).

The 'where' clause can be used to define a subset of polygons to process. See the 'where' section for further details on how to formulate a where clause.

Syntax

geom.polygonfetch(in, uidfield, out, [where]);

inthe input polygon data source
uidfieldthe unique ID field of the input feature data source
outthe output line data source
[where]the selection statement that will be applied to the line feature data source to identify a subset of lines to process (see full Help documentation for further details)

Example

geom.polygonfetch(in="C:\data\lakes.shp", out="C:\data\fetch.shp", uidfield="LAKEID");

geom.polygonfetch(in="C:\data\lakes.shp", out="C:\data\fetch.shp", uidfield="LAKEID", where="AREA > 10000");


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