NAME

r.lags - GRASS module to calculate various spatial dependence measures for all possible lags within a given image. Each measure is made by comparing two cells only for each lag azimuth and distance. The whole image is read once for each cell in the image, therefore is very computationally expensive. A Sparc 2 would typically take 1 hour to calculate a 150x150 image.

Usage:

r.lags [-sc] in=name out=name [measure=name]

Flags:

-n Calculate non-zero values only
-v Calculate semi-variogram instead

Parameters:

in=name Raster surface layer to measure

out=name Output raster containing lag map

measure=name Spatial dependence measure (Moran's I or texture)
  options: moran,texture
  default: moran

HISTORY

V1.0 written 17.6.92 to calculate Moran autocorrelation statistic.

V2.0 written 18.7.92 to also calulate Haralick's grey-tone spatial 
dependence textural measures.

V2.1 modified 18.9.95 to conform to standard GRASS program structure.


Future improvements could include (i) Option of faster, memory intensive
option; (ii) Further lag dependent measures; (iii) Cumulative lags under
some distance weighting function. (iv) Option of ignoring/including zero
values in the calculation.

Jo Wood, November, 1995
jwo@le.ac.uk
ASSIST's home

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