Correlation returns NA values

[acanion]

This is perhaps more of a clarification issue. In areas of an image where the window and shifted window all contain the same value (i.e. all in the same bin), variance = 0, and thus, correlation cannot be calculated (divide by 0). I ran glcm on WorldView satellite data in both R and ENVI, and these areas (often water) returned NA in R and 1.0 in ENVI. So it appears the R package is coded to return no data, but ENVI assigns a value of exactly 1.0. This may be good to clarify in the documentation. Thanks.