xm_raster


NAME
     xm_raster - Raster format for the xmap8 program

SYNOPSIS
     xm_raster - Input File Format

DESCRIPTION
     The raster file is a 2D or 3D raster image file.  There  are
     several formats available for input.


FORMAT
     Image Data may be imported into Xmap8 via either simple ascii files
     (format below)  or through binary files created by the netCDF programs
     available from NCAR (UCAR).  Documentation for the netCDF formats and
     software is available over the internet.

     The importing of files through netCDF must follow the output og the GMT
     program, also available over the internet.  I have installed it this
     way so that images created with GMT can be imported into Xmap8 with no
     other processing.  GMT files are generally 2D images so the third
     dimension in that case is artificially manufactured on the fly.


     The 3D netCDF files can be easily created by extending the GMT format.
     Here we simply add a few more variables and attributes so that we
     conform with the ascii files written below.


     ---------------------------------------------------------------
     Ascii image input:
     The ascii image files are simple.
     you must have the following lines:
     2 lines to describe the model followed by a long list of data values:

     lat lon nx ny nz spac-X  spac-Y
     z1 z2 z3 z4 .....(nz+1) values
     data1
     data2
     data3


     Lat-Lon are respectively the latitude and longitude of the lower left
     corner of the model.  All other points are referenced relative to this
     point.  The spacing in x-y is considered constant, given in km.  The Z
     spacng is variable and is provided by the array of values on the line
     that follows.  There must be nz+1 values since these describe the
     thickness of the layers.  Following these 2 header lines is a long list
     of numbers which represent the images.  The images are arranged
     starting from the top most layer down going from left to right across
     the array and northward, i.e. Surface-to-Depth (slowest changing
     dimension), South-to-North, West-to-East (fastest changing dimension).
     Looking down on a map of the image:

     --------------------------------------------------------------------

     (Ny-1)*Nx+1         ...       ...       Ny*Nx
     2Nx+1     2Nx+2     ...  ...  ...            2Nx+Nx
     Nx+1 Nx+2                          Nx+Nx
     1    2    3    4    5    ....etc        Nx

     --------------------------------------------------------------------
     If you  have a 2D image that does not have a "thickness" (like topography)
     then just make one up, e.g.:
     32.444 -116.43434  25 32 1 0.5 0.5
     0.0 0.3
     22
     343
     333
     etc....

     ---------------------------------------------------------------
     ---------------------------------------------------------------

     netCDF format:

     To get a netCDF file one first creates a simple file description in a
     language called CDL.  and example of a CDL file for the creation of  a
     3D image suitable for Xmap is given below.  By copying this format and
     running the utility ncgen  -o    file.cdf    file.cdl from the netcdf
     distribution one can create 3D rasters and store them in a binary
     format that is a bit more compact than the ascii format described
     above.

     See the netCDF and CDL documentation for more information.

     ---------------------------------------------------------------
     example of a cdl file which will create a cdf file suitable for reading
     into Xmap.  (The full data set has been truncated).  The data is stored
     according to the format given above, Surface-to-Depth, South-to-North,
     West-to-East).

     netcdf Puget {

     dimensions:
          side = 2 ;
          side3 = 3 ;
             Ntops = 11;
          xysize = 1500 ;
             xyzsize = 15000 ;
     variables:
             int ndims;
             double latlon(side);
          double x_range(side) ;
               x_range:units = "km" ;
          double y_range(side) ;
               y_range:units = "km" ;
          double D_range(side) ;
               D_range:units = "km" ;

          double z_range(side) ;
               z_range:units = "Sec/Km" ;
          double spacing(side) ;
          int  dimension(side3) ;
          float z(xyzsize) ;
               z:long_name = "slowness" ;
               z:scale_factor = 1. ;
               z:add_offset = 0. ;
               z:node_offset = 0 ;
               z:missing_value = 1000.0;
              float tops(Ntops);

     // global attributes:
               :title = "Puget Sound Inversion 1990" ;
               :source = "Lees & Crosson Velocity inversion 1990" ;

     data:

       ndims = 3;

      x_range = 0, 150 ;

      y_range = 0, 250 ;

      D_range = 0.0, 41.0 ;

      z_range = -12, 12 ;

      spacing = 5, 5 ;

      dimension = 30, 50, 10 ;

     latlon =  46.4000015, -123.4166641 ;

     tops =
      0.000,  2.000 , 4.000 , 6.000,  9.000, 12.000, 16.000 ,20.000, 25.000 ,32.000,  41.000;

     z =
      1000.000000 ,
      1000.000000 ,
      1000.000000 ,
         1.123851 ,
         1.021553 ,
         0.826462 ,
      1000.000000 ,
      1000.000000 ,
      1000.000000 ,
      1000.000000 ,
      1000.000000 ,
      1000.000000 ,
      1000.000000 ,
        -1.769204 ,
        -3.513751 ,
        -3.428546 ,
        -2.937757 ,
        -2.315268 ,
      1000.000000 ,
      1000.000000 ,
      1000.000000 ,
      1000.000000 ,
      1000.000000 ;
     }


SEE ALSO

xmap8      
xm_color      
xm_hypo      
xm_map       
xm_menu       
xm_origin       
xm_points
xm_raster
xm_station      
xm_well      
xm_wire      
xm_xsec      
xm_ellipse


  • Xmap8: Three-dimensional GIS for Geology and Geophysics.

    REFERENCES see article by J. M. Lees: Lees, J. M. (1995) Xmap8: Three-dimensional GIS for geology and geophysics, Seismological Research Letters: 66, 33-37.

    Address:

      
          Prof. Jonathan M. Lees
          Yale Geology Dept.
          P.O. Box 208109
          New Haven, CT  06520-8109
          (203)432-6947
          lees@love.geology.yale.edu