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Re: AI-GEOSTATS: Coordinate conversion near the poles

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  • Jim Bash
    The UTM grid system only extends to 80 degrees south (and 84 north). There is another system for polar areas, the Universal Polar Stereographic Grid System
    Message 1 of 5 , Feb 13, 2004
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      The UTM grid system only extends to 80 degrees south (and 84 north). There
      is another system for polar areas, the Universal Polar Stereographic Grid
      System (UPS). I've never had occassion to look at UPS so I can't say what
      projection is used but it, like the UTM system, is designed to have a
      certain accuracy within a zone. For UTM you can calculate distances and
      directions between any two points in a single zone to an accuracy of one
      meter in 2500 meters (people thing of UTM as being '1 meter resolution or
      accuracy'). I would assume UPS is similar.

      Good Luck!

      jim bash
      jbash@...

      On Fri, 13 Feb 2004, Ruben Roa Ureta wrote:

      > Hi list members:
      > I am now embarked in a project of fish stock assessment in the Falklands
      > using both hydroacoustics and fish density data from trawling, and of
      > course i want to use geostatistics for data analysis. I read in ai-geostat
      > archives a discussion not long ago about coordinate transformation before
      > statistical modelling to ensure proper distances. UTM coordinates were
      > recommended (the header was GeoR and memmory). The Falklands are quite
      > near the south pole so it seems to me at this location coordinate
      > conversion is a matter of relevance if i want to have a proper spatial
      > representation of the shape of the fish stock down there at the bottom of
      > the sea. The final purpose in our case is to integrate over the two
      > spatial dimensions of the fish density variable to arrive at a value of
      > total biomass. I would appreciate to have a confirmation that the UTM
      > coordinate system will account for the true shape of the Earth in my case
      > and thus i could proceed to geostatistical modelling after transforming
      > from latitude-longitude data to UTM. Thanks.
      > Ruben
      >
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    • Jim Bash
      Sorry, I didn t notice the reference to the Faulklands, just the question about near the south pole . 60S isn t that near and UTM would be fine if the study
      Message 2 of 5 , Feb 14, 2004
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        Sorry, I didn't notice the reference to the Faulklands, just the question
        about "near the south pole". 60S isn't that 'near' and UTM would be fine
        if the study stays in one zone.

        On Sat, 14 Feb 2004, Roger Bivand wrote:
        > Hold on. hold on! Look, Bergen, Norway is 60N, the Falklands, even with
        > South Georgia, are not even 60S. I protest that this isn't that near the
        > poles, even the Arctic and Antarctic circles are at 66.6...N, and that's
        > well within the 80N/S of UTM. The question was whether to transform from
        > latlong to anything projected in order to do geostats, and the answer is
        > yes, unless your geostats software itself calculates great circle
        > distances from latlong coordinates (the fields package in R does, for
        > example). So the answer is yes, use a projection of choice, UTM being a
        > possibility (depending on the W-E extent of your data), or use software
        > that respects that your data are latlong.

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