# GRASS Help System

## EXTRACTING DIGITAL IMAGERY DATA

Remotely-sensed images, such as satellite data and aerial photographs, are often available in a digital format. The data in these images can be interpreted using image processing techniques that classify image elements based on the spectral reflectance values of individual image pixels or on user-identified pixel groupings.

GRASS integrates a GIS with image processing capabilities. This allows image data to augment a GRASS database, and allows image classifications to be guided by known elements in other maps in the GIS database.

Processing of remotely-sensed imagery typically involves:

(1) extracting data from their magnetic storage media,
(2) entering extracted data into a GRASS data base,
(3) classifying pixels and elements in the image,
(4) rectifying the image to a map coordinate system and projection,
(5) correcting and enhancing the image.

GRASS commands commonly used to perform image processing are discussed in the Image Processing section. Here, only those GRASS imagery commands used to extract imagery data from magnetic tape media are discussed.

Once imagery data are obtained, they must be extracted from the magnetic tapes on which they are stored. GRASS commands exist to extract LANDSAT Thematic Mapper (TM), Multi-Spectral Scanner (MSS), and such other satellite imagery as SPOT data from half-inch magnetic tape. Header information describing the tape's content can also be extracted from tape.

The GRASS commands which perform imagery data extraction from tape are:

- i.tape.mss
- i.tape.mss.h
- i.tape.other
- i.tape.tm

For more information on a specific command, select a command and press ESC.

Specific procedures for extracting this data from tape and importing it into a GRASS database are described in the "GRASS Imagery Tutorial".

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Automatically created on: Sat Jan 8 06:50:26 2005