ndi
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Contents: Description, Arguments, Usage, Examples, Images, Related Functions, Source Supported Under Version: > 1.00
Description Generates a Normalized Difference Index map
Arguments and Return Values Arguments: 1- or 2-dimensional greyscale images representing two spectral bands Return Value: A float greyscale image
Usage Syntax: ndi(band1, band2) This function is a generalization of satellite image-processing formulae which take the form: NDI = (band1 - band2) / (band1 + band2) The most commonly-used variation is the Normalized Difference Vegetation Index, in which near-infrared is used for the first band, and red is used for the second. See this discussion of related functions for a lengthy discussion of this topic. NDI calculations will return both positive and negative values. Generally the distinction between positive and negative results provides important information. For example, in the NDVI variation, positive values generally indicate the presence of vegetation (and the greater the value, the healthier the vegetation is likely to be), whereas negative values indicate non-vegetative matter (rocks, soil, water, and so on). Some commonly-used variations from "Landsat Image Processing" (James S. Aber, 2009): Normalized Difference Vegetation Index (NDVI) = ndi(NIR, Red) ((NIR - Red) / (NIR + Red)) Green Normalized Difference Vegetation Index (GNDVI) = ndi(NIR, Green) ((NIR - Green) / (NIR + Green)) Normalized Burn Ratio (NBR) = ndi(NIR, LandSatTM7) ((NIR - LandSatTM7) / (NIR + LandSatTM7))
Examples NDVI: dv> nir 2000x1000x1 array of float, bsq format [8,000,000 bytes] dv> r 2000x1000x1 array of float, bsq format [8,000,000 bytes] dv> result = ndi(nir, r) Generating a Normalized Difference Index image. 2000x1000x1 array of float, bsq format [8,000,000 bytes] dv> max(result) 1.000000000 dv> min(result) -1.000000000 GNDVI: dv> nir 2000x1000x1 array of float, bsq format [8,000,000 bytes] dv> g 2000x1000x1 array of float, bsq format [8,000,000 bytes] dv> result = ndi(nir, g) Generating a Normalized Difference Index image. 2000x1000x1 array of float, bsq format [8,000,000 bytes] dv> max(result) 1.000000000 dv> min(result) -1.000000000 NBR (mir2 is the LandSat band 7 image): dv> nir 2000x1000x1 array of float, bsq format [8,000,000 bytes] dv> mir2 2000x1000x1 array of float, bsq format [8,000,000 bytes] dv> result = ndi(nir, mir2) Generating a Normalized Difference Index image. 2000x1000x1 array of float, bsq format [8,000,000 bytes] dv> max(result) 1.000000000 dv> min(result) -1.000000000
Images Full set of LandSat 7 imagery:
Output of ndi() (NDVI):
Output of ndi() (GNDVI):
Output of ndi() (NBR):
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Recent Library Changes Created On: 07-16-2012 |
