GEOSTATS: Spherekit: new unix shareware for spatial data analysis
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Spherekit was developed at the NCGIA (National Center for Geographic Information and Analysis)
and at the University of California, Santa Barbara (UCSB). Developers include: Cort Willmott
(University of Delaware), Rob Raskin (Jet Propulsion Laboratory), Chris Funk (NCGIA),
Scott Webber (University of Delaware), and Mike Goodchild (NCGIA).
The initial version has been released into the public domain in October 1996.
Spherekit is an integrated toolkit for spatial interpolation and comparison of
spatial interpolation algorithms. It is UNIX-based and includes a complete graphical
user interface (GUI). It uses Generic Mapping Tools (GMT) for display of interpolated fields.
The package features several unique capabilities:
Spherekit permits interpolation over continental or global scales because its computations
are based upon spherical distances and orientations. Conventional interpolations are based upon planar
projections of the earth, which produce distortions of some kind over large distances. In Spherekit,
projections are applied only for display purposes, after the interpolation has been carried out in spherical
geometry. The user can select from a wide range of interpolation algorithms and can experiment with
any associated parameter settings.
Spherekit permits the user to incorporate knowledge or information about the processes that produced the
spatial variations. This strategy, also known as "smart interpolation," is implemented through the
interpolation of user-defined, derived variables. A simple equation editor is available to produce
combinations of observation variables, and several nonlinear transforms are built-in. A digital elevation
model (DEM) is included so that elevation can be treated consistently with other variables.
Error analysis is an integrated component of Spherekit. The performance of an interpolation
method and its associated set of parameters is evaluated using cross-validation. The error at each
observation point is defined as the difference between its actual value and its estimated value using
the remaining n-1 points. The resulting error field can be displayed either at the data points or
interpolated to a regular grid, to reduce any spatial biases. Error difference fields, comparing a pair
of methods, can be easily displayed.
The available Interpolation methods are
Inverse distance weighting
Thin plate spline
Spherekit is available for download by anonymous ftp from the NCGIA.
Check the HOMEPAGE at http://www.ncgia.ucsb.edu/pubs/spherekit/main.html
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