Loading ...
Sorry, an error occurred while loading the content.

Re: GEOSTATS: Boundary delimiter algorithm!

Expand Messages
  • Charles Hendricksen
    The key word in this problem is convex hull That is the polygon that bounds all points. Shamos and Preparata have algorithms to determine the convex hull.
    Message 1 of 4 , Feb 7, 1997
    • 0 Attachment
      The key word in this problem is "convex hull" That is the polygon that
      bounds all points. Shamos and Preparata have algorithms to determine the
      convex hull.


      Charlie Hendricksen veritas@...

      --
      *To post a message to the list, send it to ai-geostats@....
      *As a general service to list users, please remember to post a summary
      of any useful responses to your questions.
    • roswell marjorie
      Check out the bottom of http://www.sfiltd.com/products.htm The Convex Hull Generator creates the polygon which you would get if each datapoint were a nail in
      Message 2 of 4 , Feb 7, 1997
      • 0 Attachment
        Check out the bottom of

        http://www.sfiltd.com/products.htm

        "The Convex Hull Generator creates the polygon which you would get if each
        datapoint were a nail in a board and youstretched a rubber band around the
        outside of all of them. "

        This is a MapInfo-based solution.


        Margie


        On Fri, 7 Feb 1997, Paloma Urbano Lopez de Meneses wrote:

        > Hello to everyone!
        >
        >
        > I am trying to delimit a boundary out of a disperse set of points
        > considering only the most external ones.
        > The example should be something like the following,
        >
        > + +
        > +
        > + +
        > +
        > + +
        >
        > This are the disperse points
        >
        > The algorithm will delimited the outside boundary.
        >
        > +-----+
        > / + \
        > / + +
        > + |
        > \__ +____+
        >

        _________________________________________________________
        Marjorie Roswell, Spatial Analyst
        UMBC Center for Health Program Development and Management
        1000 Hilltop Circle Fx: (410)455-6850
        Baltimore, MD 21250 E: roswell@...
        Ph: (410)455-6802 http://umbc.edu/~roswell/mipage.html
        _________________________________________________________

        --
        *To post a message to the list, send it to ai-geostats@....
        *As a general service to list users, please remember to post a summary
        of any useful responses to your questions.
      • Roberto Bruno
        ... Dear Paloma, I cannot help you about generic algorithms you ask for, but I suggest you to make sound use of: a) the phisical meaning of the boundary
        Message 3 of 4 , Feb 7, 1997
        • 0 Attachment
          paloma@... wrote:
          >
          > Hello to everyone!
          >
          > I am trying to delimit a boundary out of a disperse set of points
          > considering only the most external ones.
          > The example should be something like the following,
          >
          > + +
          > +
          > + +
          > +
          > + +
          >
          > This are the disperse points
          >
          > The algorithm will delimited the outside boundary.
          >
          > +-----+
          > / + \
          > / + +
          > + |
          > \__ +____+
          >
          > At the moment we have been triangulating the points and obtaining the
          > outline, however we are interested in an algorithm which would
          > recognize the most external points of the area and use them to
          > create a boundary polygon.
          >
          > Any help on this, useful web pages or literature would be appreciated.
          >
          > Thank you in advance,
          >
          > Paloma Urbano

          Dear Paloma,

          I cannot help you about generic algorithms you ask for, but I suggest
          you to make sound use of:
          a) the phisical meaning of the boundary polygon that you are looking for;
          b) the nature of data linked to the locations.
          In effect in many cases you could get good results by just exploiting the tools
          of geostatistics (of course used properly) and the selection criteria.
          For example, if in each point you have a thickness value of a geological body
          and you are looking for an evaluation of the total volume, you could make a
          kriging of the thickness at the nodes of a grid superimposed to the potential
          interest area.
          The boundary could then be defined on the base of the selection made on
          kriged values at the grid nodes. You just have to adopt one (or more) sound
          criteria :
          - a cut off value on the estimation variance (absolute or relative);
          - a selection of nodes with a consistent probability of having a positive
          thickness, but considering a lower limit of a confidence interval
          [Z*- k sigma2(Z*->Z), k>=0.];
          - the range value of variogram model of the variable at hand;
          - ... and so on, depending on the nature of your problem (a "noise level" is
          a variable quite different from "thickness" or from a "proportion", and so is
          the associated problem).

          Even if you have not the actual values of your (regionalized) variable,
          in my opinion you should refer to the true nature of your problem in choosing the
          boundarying procedure.

          I suggest you to address a specific/technical literature of your working field,
          and to examine not a "blind" or generic procedure, but that one which you
          select as the most proper when looking at the heart of your problem.

          Best regards.

          Prof. Roberto BRUNO
          Dip. Chemical, Mining & Environmental Technlogies Engineering
          Univ. of BOLOGNA, Italy
          Tel.(+39-51) 6443393; fax (+39-51) 6443392
          E-mail: SCIENMIN2@...
          --
          *To post a message to the list, send it to ai-geostats@....
          *As a general service to list users, please remember to post a summary
          of any useful responses to your questions.
        Your message has been successfully submitted and would be delivered to recipients shortly.