ArcGIS 10 – Selecting Polygons with Minimum Internal Straight Line Value

arcgis-10.0linepolygon

I have a map of polygons representing forest stands. I am trying to sort through them to find those polygons that have a minimum internal distance of 200 m in a straight line (my field sampling will consist of ground truthing the stands, and will require a 200 m line to fall within the stand).

I have tried to find if there is an automated way to do this, which there doesn't appear to be. There was something made thats no longer applicable for arcgis 10 ( http://www.jennessent.com/arcview/longest_lines.htm ).

If it comes to it, I don't mind eyeballing the distance, and drawing a line myself. But I can't seem to figure out a way to draw it so that I can pull geographic coordinates off of it. As in, when I draw two points I somehow convert the drawn points to a feature set of X and Y coordinates. All I can figure out is just doing it by hand, and viewing the values at the bottom right of the screen and recording them by hand.

Thanks in advance, and let me know if you need anything cleared up, not great at explaining my problems (probably why I can't find anything online too).

Ayden

Best Answer

It sounds like the "Calculate Fetch in Polygons" command in SpatialEcology's Geospatial Modelling Environment (GME) should produce what you are looking for.

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).

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