## GRASS GIS 8.4.1 Reference Manual

Geographic Resources Analysis Support System, commonly referred to as GRASS GIS, is a Geographic Information System (GIS) used for geospatial data management and analysis, image processing, graphics/maps production, spatial modeling, and visualization. GRASS is currently used in academic and commercial settings around the world, as well as by many governmental agencies and environmental consulting companies.

This reference manual details the use of modules distributed with Geographic Resources Analysis Support System (GRASS), an open source (GNU GPLed), image processing and geographic information system (GIS).

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### Imagery commands:

i.albedo | Computes broad band albedo from surface reflectance.
i.aster.toar | Calculates Top of Atmosphere Radiance/Reflectance/Brightness Temperature from ASTER DN.
i.atcorr | Performs atmospheric correction using the 6S algorithm.
i.band.library | Prints available semantic label information used for multispectral data.
i.biomass | Computes biomass growth, precursor of crop yield calculation.
i.cca | Canonical components analysis (CCA) program for image processing.
i.cluster | Generates spectral signatures for land cover types in an image using a clustering algorithm.
i.colors.enhance | Performs auto-balancing of colors for RGB images.
i.eb.eta | Actual evapotranspiration for diurnal period (Bastiaanssen, 1995).
i.eb.evapfr | Computes evaporative fraction and root zone soil moisture.
i.eb.hsebal01 | Computes sensible heat flux iteration SEBAL 01.
i.eb.netrad | Net radiation approximation (Bastiaanssen, 1995).
i.eb.soilheatflux | Soil heat flux approximation (Bastiaanssen, 1995).
i.emissivity | Computes emissivity from NDVI, generic method for sparse land.
i.evapo.mh | Computes evapotranspiration calculation modified or original Hargreaves formulation, 2001.
i.evapo.pm | Computes potential evapotranspiration calculation with hourly Penman-Monteith.
i.evapo.pt | Computes evapotranspiration calculation Priestley and Taylor formulation, 1972.
i.evapo.time | Computes temporal integration of satellite ET actual (ETa) following the daily ET reference (ETo) from meteorological station(s).
i.fft | Fast Fourier Transform (FFT) for image processing.
i.gensig | Generates statistics for i.maxlik from raster map.
i.gensigset | Generates statistics for i.smap from raster map.
i.group | Creates, edits, and lists groups of imagery data.
i.his.rgb | Transforms raster maps from HIS (Hue-Intensity-Saturation) color space to RGB (Red-Green-Blue) color space.
i.ifft | Inverse Fast Fourier Transform (IFFT) for image processing.
i.image.mosaic | Mosaics several images and extends colormap.
i.in.spotvgt | Imports SPOT VGT NDVI data into a raster map.
i.landsat.acca | Performs Landsat TM/ETM+ Automatic Cloud Cover Assessment (ACCA).
i.landsat.toar | Calculates top-of-atmosphere radiance or reflectance and temperature for Landsat MSS/TM/ETM+/OLI
i.maxlik | Classifies the cell spectral reflectances in imagery data.
i.modis.qc | Extracts quality control parameters from MODIS QC layers.
i.oif | Calculates Optimum-Index-Factor table for spectral bands
i.ortho.camera | Select and modify the imagery group camera reference file.
i.ortho.elev | Select or modify the target elevation model.
i.ortho.init | Interactively creates or modifies entries in a camera initial exposure station file for imagery group referenced by a sub-block.
i.ortho.photo | Menu driver for the photo imagery programs.
i.ortho.rectify | Orthorectifies an image by using the image to photo coordinate transformation matrix.
i.ortho.target | Select or modify the imagery group target.
i.ortho.transform | Computes a coordinate transformation based on the control points.
i.pansharpen | Image fusion algorithms to sharpen multispectral with high-res panchromatic channels
i.pca | Principal components analysis (PCA) for image processing.
i.rectify | Rectifies an image by computing a coordinate transformation for each pixel in the image based on the control points.
i.rgb.his | Transforms raster maps from RGB (Red-Green-Blue) color space to HIS (Hue-Intensity-Saturation) color space.
i.segment | Identifies segments (objects) from imagery data.
i.signatures | Manage imagery classification signature files
i.smap | Performs contextual image classification using sequential maximum a posteriori (SMAP) estimation.
i.spectral | Displays spectral response at user specified locations in group or images.
i.target | Targets an imagery group to a GRASS location and mapset.
i.tasscap | Performs Tasseled Cap (Kauth Thomas) transformation.
i.topo.corr | Computes topographic correction of reflectance.
i.vi | Calculates different types of vegetation indices.
i.zc | Zero-crossing "edge detection" raster function for image processing.

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© 2003-2025 GRASS Development Team, GRASS GIS 8.4.1 Reference Manual