i.tape.spot

NAME

i.tape.spot - An imagery function that extracts SPOT imagery from half-inch tape.
(GRASS Image Processing Program)

SYNOPSIS

i.tape.spot

DESCRIPTION

i.tape.spot is a program that extracts SPOT imagery from 9-track, half-inch tape.

This program must be run in a LOCATION_NAME with an x,y coordinate system (i.e., a coordinate system with projection 0). For further information regarding this LOCATION_NAME type refer to the imagery manual entry.

The first prompt in i.tape.spot asks the user for the tape device name.

Enter tape device name:

This is sometimes /dev/rmt0 (for a half-inch tape having a density of 1600 bpi), but this varies with each machine.

The next prompt is:

Mount SPOT tape and hit RETURN -->

IMAGE IDENTIFICATION MENU

The first menu in the program asks the user for information about the data.

      Please enter the following information

TAPE IDENTIFICATION:                             __

IMAGE DESCRIPTION:                               __

TITLE FOR THE EXTRACTED CELL (RASTER) FILES:     __

AFTER COMPLETING ALL ANSWERS, HIT <ESC> TO CONTINUE
              (OR <Ctrl-C> TO CANCEL)

This program automatically reads the satellite name, tape product code, instrument name, interleaving indicator, spectral mode, preprocessing level and work order number into the field for TAPE IDENTIFICATION. The mission, path, row, scene shift, scene center date and time, orientation, incidence, azimuth, elevation angle, and absolute calibration coefficients and offsets are automatically entered into the field for IMAGE DESCRIPTION. User can type in any other messages into the two sections and a description as the TITLE of raster map layer. The second menu is:

                SPOT IMAGE EXTRACT
    Please select region of the image to extract

             start row: 0______(1-3002)
               end row: 0______(1-3002)

             start col: 0______(1-3166)
               end col: 0______(1-3166)


AFTER COMPLETING ALL ANSWERS, HIT <ESC> TO CONTINUE
              (OR <Ctrl-C> TO CANCEL)

The numbers in parentheses are the total number of rows and columns on the tape including zeros (filler). This information and additional information can also be obtained by running the program m.examine.tape. m.examine.tape will read any tape and provide the user with the number of files on a tape, the number of records on a tape, and the record lengths. Any subset of the image on the tape may be extracted. For a discussion of row and column extraction see the subheading enTITLEd ROW AND COLUMN EXTRACTION below.

The next menu is:

  Please mark an x by the bands you want extracted

                      _____ 1
                      _____ 2
                      _____ 3

AFTER COMPLETING ALL ANSWERS, HIT <ESC> TO CONTINUE
              (OR <Ctrl-C> TO CANCEL)

SPOT imagery has three bands, but the user may want to extract a subset of these bands. See the subheading in this entry enTITLEd ROW AND COLUMN EXTRACTION.

The user then is asked to enter the prefix/group name for the raster band files to be created. This name will precede each band file extracted into GRASS. For example, if two bands are extracted the following two band files will result:

prefixname.1
prefixname.2

The specified prefixname will also automatically become the name for the imagery group file being created. Each image or subset (i.e., each run of i.tape.spot) should be given a unique prefix/group name.

The extraction process will begin by first skipping a number of files which are not data or not requested, advancing to the first band requested, forwarding to the requested column, and then reading the data. After extracting the requested rows and columns from each band, the program creates support files for the raster band map layer. The percent completion of the extraction is displayed on the screen. Because sometimes SPOT imagery is very large and is stored in multiple tape sets, the program is designed to read image by pausing when the tape need to be changed and inform the user to mount and load next tape. The number of tapes required to store one scene depends on the number of bytes per inch (bpi) in which the data are stored.

The extracted band files will be listed as raster map layers available in the current MAPSET and may be displayed using the GRASS commands d.display, d.rast, or i.points.

ROW AND COLUMN EXTRACTION

The display options in GRASS allow the user to locate rows and columns on the digital image. If enough disk space is available, one band of an entire image or one band of a portion of an image known to contain the area of interest, can be extracted and displayed. The measurements option in d.display, or d.where (following use of d.rast) will echo x and y coordinates to the screen. (These coordinates will display negative numbers in the north-south direction, but ignoring the negative sign will yield the row number.) See the imagery manual entry for further explanation.

Each scene of a SPOT image contains filler on both the left and right sides of the quad. The user may want to identify the row and column numbers in order to exclude the filler. This filler will otherwise be extracted with the image and take up unnecessary disk space.

If a photograph of the digital image is available, the rows and columns to be extracted can be determined from it by associating inches with the total number of known rows and columns in the scene. For example, if the total length of the photograph is 12 inches, the total number of rows on the tape is 2000, and the northwest corner of the area of interest begins 2 inches from the top of the photo, then:

12" / 2000 rows = 2" / x rows

x = 333.333

The northwest corner of the area of interest starts at row 333. The starting row, ending row, starting column, and ending column can be calculated in this manner.

NOTES

After extracting an image from tape the geographic region definition in the x,y coordinate LOCATION_NAME will be set based upon the extracted rows and columns from the tape. The relationship between the image rows and columns and the coordinates of the geographic region is discussed in the imagery format manual entry.

This program is interactive and requires no command line arguments.

AUTHOR

Tao Wen, University of Illinois at Urbana-Champaign

Last changed: $Date: 2002/01/25 05:45:33 $