i.tape.tm

NAME

i.tape.tm - An imagery function that extracts LANDSAT Thematic Mapper (TM) imagery from half-inch tape.
(GRASS Image Processing Program)

SYNOPSIS

i.tape.tm

DESCRIPTION

i.tape.tm is a program that extracts LANDSAT Thematic Mapper (TM) imagery from half-inch tape.

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

The first prompt in i.tape.tm asks the user for the 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:

Please mount and load tape, then 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 Raster (Cell) Files:     __

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

This program automatically enters the scene ID number into the field for Tape Identification. The mission, path, row, quadrant, date, and whether the image is corrected is automatically entered into the field for Image Description.

The second menu is:

              THEMATIC MAPPER EXTRACT
please select the desired tape window (geographic 
region definition) to extract

             first row: _______(1-2984)
             last row: _______(1-2984)

             first col: _______(1-4220)
             last col: _______(1-4220)


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 lengthes. 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 make an x by the bands you want extracted

                      _____ 1
                      _____ 2
                      _____ 3
                      _____ 4
                      _____ 5
                      _____ 6
                      _____ 7

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

TM imagery has 7 bands, but the user may want to extract only 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 for the raster band files to be created. This name will precede each band file extracted into GRASS. For example, if three bands are extracted the following three band files will result:

prefixname.1
prefixname.2
prefixname.3

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

The extraction process will begin by first skipping the number of specified files, advancing to the first band requested, and then reading the tape. After extracting the requested rows and columns for 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 TM imagery is divided into four quads and is stored in multiple tape sets, the program is designed to read one quad at a time. The number of tapes required to store one quad depends on the number of bytes per inch in which the data is stored. If more than one tape is required to store one quad, the program will pause and inform the user to mount the next tape.

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.

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 manual entry.

This program is interactive and requires no command line arguments.

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 quad of a TM 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.

AUTHOR

Michael Shapiro, U.S.Army Construction Engineering Research Laboratory