[GIS] Finding long axis of irregular polygon using ArcGIS Desktop

arcgis-desktoppolygon

I need some help in how to find the long axis of an irregular shaped ellipse using ArcGIS Desktop.

I have found the centroid but don't know how to determine the longest distance.

You can use the Minimum Bounding Geometry (Data Management) tool.

Use the 'Convex Hull' option.

This will create several new fields:

MBG_Length will give you the distance between the farthest points (antipodes)

The MBG_APOD points will give you the coordinates of the new antipodal line

Quick and dirty: If the "false" centroid is not in the polygon use the nearest vertex to that point.

That is a nice piece of code, but not nearly as nice as (assuming your table is in geographic coordinates, if not just remove the casts to geography)

CREATE TABLE mytable_distances AS
SELECT a.id, b.id, ST_Distance(a.geom::geography, b.geom::geography) as distance
FROM mytable a, mytable b;

Have I mentioned that spatial databases rock? They do. Oh, they do.