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2262RE: [ai-geostats] polygon changes

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  • Colin Robertson
    Nov 1, 2005
    • 0 Attachment
      Dear Mr. Boogaart,

      Thanks for your response and I'll see if I can be clearer in my question.
      My interest is in detecting and characterizing changes in polygons between
      T1 and T2. So essentially, comparing two polygon datasets. I think it's a
      little narrower than space and time in Vector GIS, as there are numerous
      methods available for point data, and while one way is to use polygon
      centroids with spatial information attached as attributes, I feel this does
      not effectively capture the complexity of the polygon data (ie boundary
      complexity, orientation, proximity to other features etc).

      So with two polygon datasets which are derived from peak values in an
      intensity surface (moving infestation), some polygons in T1 will intersect
      polygons in T2, some will not. The polygons therefore vary in space and in
      time. So my concern is, where there is intersection, can all of a polygon
      in T2 be considered to have come from the intersecting polygon in T1? Is
      there consistent shape complexity between both? Where there is no
      intersection, but proximity (to some threshold), can a relationship between
      T1 and T2 be established? More importantly, what spatial relationships
      (beyond spatial intersection) can be detected? How can I detect shrinking,
      expanding, moving, coalescing? Much information can be derived from
      visually looking at polygons in T1 and T2, but I am hoping to find a method
      to characterize / detect the change more formally.

      I hope this clears up my original post. As far as my background goes, I'm
      just starting a graduate thesis, and have completed a bachelors(geography)
      and advanced diploma(GIS). So I have much to learn about spatiotemporal

      Thanks for your interest,


      -----Original Message-----
      From: Gerald van den Boogaart [mailto:boogaart@...]
      Sent: Tuesday, November 01, 2005 4:30 AM
      To: Colin Robertson
      Cc: 'AI Geostats mailing list'
      Subject: Re: [ai-geostats] polygon changes

      Dear Mr. Robertson,

      > Do any of you have experience/advice on spatiotemporal analysis of
      > polygon data?
      To me your question reads like: Did anybody of you at any time considered
      in vektor GIS. And clearly one can lecture hours on that, while "real world"

      GIS Systems typically don't support that properly. However to give any sort
      of advice one needs a more specific question:

      How do your polygones vary?
      What do they represent?
      Do they overlap in space / in time / in spacetime?
      Are they polygons by nature or just areas approximated by polygons.
      What are the questions, you would like to ask your data?
      Do you have a polygon process consisting of many polygons or do you observe
      one individual polygon changing over time.
      Do your polygons change smoothly or discontinuesly.
      Are the polygons individuals or perculations?
      Do they form a coverage (i.e. is everything occupied)?
      Is there a map of relevant additional covariates?
      Is their any sort of representatitivty in the dataset?
      What is your personal background (no need of writing well known things to
      Are you writing a thesis on the theory of analysing polygons or do you work
      a specific problem.

      Best regards,
      Gerald v.d. Boogaart

      Am Samstag, 29. Oktober 2005 02:12 schrieben Sie:
      > Dear List,
      > Do any of you have experience/advice on spatiotemporal analysis of
      > polygon data? I've read about Sadahiro's methods
      > (http://okabe.t.u-tokyo.ac.jp/okabelab/sada/docs/pdf/CSIS%20DP25.pdf )
      > on the subject and his ideas look promising to me, but I have not seen
      > them implemented anywhere, nor have I seen anything comparable. Has
      > anyone have experience with these or other methods for analyzing changes
      > in polygons over time?
      > Thanks,
      > Colin Robertson
      > MSc Candidate
      > Dept of Geography
      > University of Victoria
      > (250) 885-8065
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