88GEOSTATS: large dataset in geographic coordinates
- Feb 10, 1997Hi,
I would like some advise on tools for doing spatial analysis on two
large, multivariate spatial datasets. (I've checked several of the
packages listed in the ai-geostats home page, but its not clear if they
will do what I want.) Both of the datasets are in the form of text
files and the spatial locations are given in geographic (lat-lon)
coordinates. There are more than 3,000 points in each set and the
coverage is most of North America. I would like to do an analysis of
spatial autocorrelation on both datasets, and an analysis of their
cross-correlation, i.e., to test the hypothesis that one of the
datasets is influencing the other.
The main stumbling block has been calculating the distances among the
lat-lon coordinate pairs. I have been using a combination of PERL and
the "geod" program from the PROJ.4 distribution. Unfortunately,
"geod" is written in such a way that it is extremely difficult to call
repeatedly from within PERL. (If someone could provide documentation
for the PROJ.4 library routines, I would consider encapsulating them
in a perl module.) I can't just dump all the pair-wise comparisons
and then run them through "geod" because it would require at least 2GB
to store the intermediate data. (Probably more, I ran out of
memory/disk space long before it finished.)
So here are a couple of questions:
1) If I only need +/-1km precision in my distances, is there an
alternative to PROJ.4, i.e., a simple formula for calculating the
2) Can I transform the data points into some Cartesian coordinate
system and then use simple linear distances? PROJ.4 has many planar
projections, but its not clear to me that distances wouldn't become
distorted over an area the size of North America.
3) Are there any (free Unix ;-) geostats programs that work in
geographic coordinates and can process large data sets?
Finally, are there standard methods to test for spatial dependence of
one dataset on another?
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