Hi Hans,
I just wanted to say thanks for your response. I actually ended up using a pretty unsophisticated approach. I'm using AttributeRounder to round the area attribute to a whole number. And I use that in the ChangeDetector. That way I'm at least disregarding the changes under 1 sq foot. Thanks again, Angela Deegan GIS Specialist, I. S. Dept Helix Water District 619 667 6245 ________________________________ From: fme@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Hans van der Maarel Sent: Wednesday, January 24, 2007 11:13 PM To: fme@yahoogroups.com Subject: Re: [fme] ChangeDetector - when comparing geometries (polygons) which are very similar Hi, > I am comparing two datasets of polygons using ChangeDetector, matching > on Geometry only (2D). The problem is that in some cases, there is > negligible change in the polygons. And these negligible changes resuls > in records being added to the "Added" and "Deleted" outputs. > > I would like for those changes in polygon area which I consider > negligible (say under 1 square foot) to be either disregarded or > categorized separately so that my sets of "Added" and "Deleted" are > smaller and more manageable. > > Anyone know of a way to achieve this? Well... negligible change is still change :) The trouble with automatic vs human processing on this is that it's very hard to give the automatic way the same 'fuzzy logic' as a human operator would apply. There's several things you can try: 1: - OGCGeometryExtractor on the new features to save the new geometry - AnchoredSnapper with a certain tolerance to snap new back to old - ChangeDetector - OGCGeometryReplacer to bring back the new geometry 2: - Calculate area for old and new - Matcher (assuming there is some unique id) - ExpressionEvaluator and Tester to calculate and test for the difference in area The area-calculation route is a bit risky, you can have a wildly different polygon, but still have exactly the same amount of sq. feet. Hope this helps. -- Hans van der Maarel Red Geographics Zevenbergsepoort 44b www.redgeographics.com 4791 AE Klundert [EMAIL PROTECTED] <mailto:hans%40redgeographics.com> The Netherlands phone: +31-168-401035
