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I'm getting consistent, weird results from using Minimum Bounding Geometry to make circle polygons. I'm not sure if a datum issue, but I'm leaning more towards something wrong with Minimum Bounding Geometry tool. Here's the situation:

Goal is to acquire diameter in meters from minimum bounding polygon circles.

Python script works as follows:

  • Import Lat/Lon values with MakeXYEvent Layer (setting GeoCoordSys to D_North_American_1983)
  • Copy Features
  • Project points (to North America Albers Equal Area Conic)
  • Create Min. Bound Polygons around groups of points (ranging from 2 to over 50 points in a group).

Results seem reasonable for most polygons, however there are a good portion that the resulting circles wrap the globe. In several cases the points are clearly grouped in a small area off the coast, and the polygon is covering an enormous area of land, not even overlapping points. This in combination with "inconsistent extent" error makes me think it's a datum/project issue.

Troubleshooting efforts so far include

  1. Points used to create the erroneous min bound circle outputs do not appear to have unusual lat/lon values.

  2. Running Min. Bound Polygon to create a convex hull on points that were consistently creating crazy circles. Convex Hull created seemingly reasonable results.

  3. Using convex hull polygon as input for min bound circle, and created same enormous circle.

Have you seen this before? Is this a case of choosing the wrong projection/datum? An error in Arc? An error in Min Bounding Geometry tool?

Thanks for input!

Sharon

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1 Answer 1

up vote 3 down vote accepted

If you need the minimum area bounding circle, then look at this link (Bounding Containers). Make sure you are using projected coordinates. Shapefiles are supported, and it has been tested in ArcMap 10 but should work in 10.1. The fundamental python code for other platforms is included within the zip file.

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Hi Dan - thanks for responding and sharing the Bounding Containers toolbox. I encountered the same error on a test run as user Kenbuja on Aug 24, 2011, in that it gave Error 999999 to save to a geodatabase. –  SharonB Mar 7 '13 at 16:41
    
And, it did work when saved outside a geodatabase. Are there known bugs with Arc's minimum bounding tool? –  SharonB Mar 7 '13 at 16:48
    
The BoundingContainers tool does seem to work well - as in, the points are all actually contained within their associated polygons. I have been running it "by hand" because as a relatively novice Python scripter, I had trouble implementing the Bounding Containers module into my own Python script for this project. –  SharonB Mar 7 '13 at 20:07
    
As indicated, it works with shapefiles and not stuff in Geodatabases. You can't use my scripts within your own, use the provided toolbox, then use the resultant data. It is impossible for me to cover all possible workflows and platforms –  Dan Patterson Mar 7 '13 at 20:19
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