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Re: GEOSTATS: spatial correlation method

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  • Isobel Clark
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    Message 1 of 2 , Nov 1, 2000
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      > How can I assess the spatial correlation between
      > these two representations
      > of the same road ?

      If your information has the same spatial co-ordinates
      in both sets, you can produce a co-located cross
      semi-variogram by simply calculating the covariance
      for each lag:

      (g_i - g_j)(f_i - f_j)

      where g and f are the two variables, i and j are two
      locations a specified distance apart. Average over all
      pairs the same distance apart and divide by two. This
      is exactly analogous to calculating the covariance
      between the two at that specified distance:

      (g_i - gbar)(f_j - fbar)

      only you don't need the two means. If your samples are
      not at the same locations you need the non-co-located
      semi-variogram, referred to by some authors as a
      "pseudo cross semi-variogram" and given as standard in
      Noel Cressie's book. The basic form of this is

      (g_i - f_j)^2

      notation as above. This assumes that the two variables
      have the same mean or have been standardised somehow.

      Kriging is always the same. Watch out for Volume 2 of
      Practical Geostatistics -- PG2001. Lots of
      explanations there.

      Isobel Clark
      drisobelclark@...
      http://uk.geocities.com/drisobelclark
      Isobel Clark



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