


NAME: Convex Hulls v. 1.24 (Click Name to Download) Aka: conv_hulls_pts.avx Last modified: February 11, 2008 TOPICS: ArcView 3.x, View, Analysis, Tools, Polygon, Hull, Convex, Extent, Rectangle AUTHOR:
Jeff Jenness DESCRIPTION: This tool generates convex hulls (also known as minimum convex polygons) around sets of points. These polygons represent the minimum possible area that contains all the points and can be imagined as a rubber band stretched around the points. This tool can generate these hulls based a set of selected points, a set of all the points or by sets of points with common attribute values.
This tool also converts Multipoint, Polyline and Polygon themes to either Rectangular Extent polygon themes or Convex Hull polygon themes. OUTPUT: This tool will produce a polygon shapefile with one or more polygons representing your convex hulls. The polygon will contain the following fields in the attribute table:
REQUIRES: This extension requires that the file "avdlog.dll" be present in the ArcView/BIN32 directory (or $AVBIN/avdlog.dll) and that the Dialog Designer extension be located in your ArcView/ext32 directory, which they usually are if you're running AV 3.1 or better. The Dialog Designer doesn't have to be loaded; it just has to be available. If you are running AV 3.0a, you can download the appropriate files for free from ESRI at: http://support.esri.com/index.cfm?fa=downloads.patchesServicePacks.viewPatch&PID=25&MetaID=483 REVISIONS: The 1.2 revision (February 19, 2004) adds the option to convert Multipoint, Polyline or Polygon themes to either Rectangular Extent or Convex Hull themes. The 1.21 revision (April 11, 2005) modifies the output to reflect the view projection. Version 1.22 (May 24, 2006) fixes a rare error that produces an “AVArray Index” error, caused by a situation in which the leftmost or rightmost points lie in a column with identical Xvalues, and when there are more values in this column than there are unique Xvalues in the dataset. Version 1.22 also adds a Help menu item to check the Convex Hull scripts for errors. Version 1.23 (February 28, 2007) is a minor update that allows the extension to work with PointZ and PointM shapefiles. The hulls are still 2dimensional, based only on the X and Ycoordinates of the points. Version 1.24 (February 11, 2008): A minor update that checks for null points before building a convex hull. Recommended Citation Format: For those who wish to cite this extension, the author recommends something similar to: Jenness, J. 2008. Convex hulls around points (conv_hulls_pts.avx) extension for ArcView 3.x, v. 1.23. Jenness Enterprises. Available at: http://www.jennessent.com/arcview/convex_hulls.htm. Please let me know if you cite this extension in a publication ( jeffj@jennessent.com ). I will update the citation list to include any publications that I am told about. General Instructions:
Converting Points to Convex Hulls
Converting Point, Line or Polyline themes to Rectangular Extent Polygons:
Converting Point, Line or Polyline themes to Convex Hull Polygons:
Troubleshooting: If you encounter some strange crash, please click the menu item “Check ‘Convex Hull’ Scripts” in either the View or Project Help menu. Click this as soon as you are able to following the crash. With any luck, that function will generate a report with enough information for the author to find and fix the problem. Enjoy! Please contact the author if you have problems or find bugs. Jeff Jenness
jeffj@jennessent.com An Adobe PDF version of this manual is included with the extension.
Please visit Jenness Enterprises ArcView Extensions site for more ArcView Extensions and other software by the author. We also offer customized ArcViewbased GIS consultation services to help you meet your specific data analysis and application development needs. 