Import Transect Data

Import Transect Data (Geometric Shape)

This command is used to import transect data and to convert it into a geometric shape defined either in pixel or geodetic (WGS-84) co-ordinates from a text file.

Transect data files are text files and have the default extension .txt. Each line in the file corresponds to a single vertex point of the geometric shape. Co-ordinates are stored in columns separated by whitespace characters (space or tabulator). All co-ordinates refer to a pixel's upper left corner. A file can have a header line in order to specify column names.

Transect Data Files without Header Line

Columns 1 and 2 are mandatory and contain the point's pixel X co-ordinate and Y co-ordinate, respectively. Columns 3 and 4 are optional and contain the point's geodetic latitude and longitude co-ordinates defined on the WGS-84 ellipsoid in decimal degree. Other columns are ignored:

column 1: mandatory X co-ordinate given in pixels
column 2: mandatory Y co-ordinate given in pixels
column 3: optional latitude in decimal degree
column 4: optional longitude in decimal degree
column 4 + i: optional additional data

If the current product is geo-coded, which is always true for ENVISAT products or map projected products, and the geodetic co-ordinates are given, the pixel co-ordinates are rejected. In this case, VISAT computes the actual pixel co-ordinates for the current product.

For example (note, 5th column is ignored): 

        207 390 43.167255 -7.7339296 38.732
        208 389 43.175785 -7.718502 48.529
        208 388 43.18614 -7.715622 50.889
        209 387 43.19465 -7.7002006 38.709
        ...

Transect Data Files with Header Line

The file can optionally contain a header line. The header line contains column names which are also expected to be separated by whitespace characters. Some column names have a special meaning for the import command, since they specify the alternate column for the recognized co-ordinates. Special names can appear in any order and are letter case insensitive. They are:

x, pixel_x or pixel-x: X co-ordinate given in pixels
y, pixel_y or pixel-y: Y co-ordinate given in pixels
lat or latitude: latitude in decimal degree
lon, long or longitude: latitude in decimal degree
other names: ignored

Either pixel or geodetic co-ordinates must be given. Again, if geodetic co-ordinates are present, they override the point's pixel co-ordinate if present, since they are recomputed by VISAT. The columns can appear in any order.

For example (note, columns named "Index" and "radiance_11" are ignored): 

        Index Pixel-X Pixel-Y Lat Lon radiance_11
        0 205 393 43.139843 -7.767645 35.16
        1 206 392 43.148373 -7.752228 32.764
        2 206 391 43.158722 -7.749352 35.751
        ...