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1412Re: AI-GEOSTATS: Coordinate conversion near the poles

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  • Roger Bivand
    Feb 14, 2004
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      On Fri, 13 Feb 2004, Jim Bash 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.

      Roger

      (writing from just North of 60N!!)

      >
      > 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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      >
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      >

      --
      Roger Bivand
      Econonic Geography Section, Department of Economics, Norwegian School of
      Economics and Business Administration, Breiviksveien 40, N-5045 Bergen,
      Norway, voice: +47-55959355, fax: +47-55959393; Roger.Bivand@...



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