Editing DSP

The DSP takes unsigned short (16-bit) integer data. Our various command-line data converters can help bring data in from pretty much any existing format, including image data, via various processing commands. If the data were in png image format, for example (which is basically 3-channel 8-bit integer data), the data could be prepared with a combination of 'png-pix', 'pix-bw', and 'cv'.  

If you type the 'in' command, it will prompt you for each parameter individually and that should help some. For the DSP, the main parameters are: the source of the height data, the width (number of points in the X direction) and length (number of points in the Y direction) of the input data, width/length/height scaling factors, and whether to smoothly interpolate between cells (0 = do not interpolate, 1 = interpolate).

A DSP primitive is an array of cells initially defined by points in the X-Y plane as positive heights from Z = 0.  The DSP can then be transformed to other orientations and positions.  The number of cells is (numX * numY).

In [[mged]] create a dsp object of width 142, length 150, no interpolation, cut direction 'ad', cell size 1 (in current units), and unit elevation 0.005 (in current units):

  mged> in dsp1.s dsp f Ex1.dsp 142 150 0 ad 1 0.005

  mged> B dsp1.r

  mged> ae 270 90

[[Image:Ex1rt.png]]

  $ bwmod -m-1 -a255 < Ex1.bw > Ex1n.bw

And make another dsp in the same manner as before:

 

 

 

  mged> B dsp2.r

  mged> ae 270 90

[[Image:Ex2rt.png]]

Again, you could play with various parameters to get the desired look. You could also create the negative as we did with example 1 and see the results:

 

A DSP object can be created manually or programmatically by creating an ASCII data file as input using the BRL-CAD utility asc2dsp to convert it directly to the DSP binary format.  An easy way to create the input file for asc2dsp is to first create it row by row in natural form with the top row being the desired top row and so on in desired viewing order.  Then take the finished file and filter it through the Unix utility tac which will reverse the order of the rows (lines).   

For example, let's create the letter "T" for viewing in the X-Y plane.

$ cat t-normal.asc

Now reverse the file:

  $ tac t-normal.asc > t-reversed.asc

and see the result in perfect form for asc2dsp:

$ cat t-reversed.asc

Finally, create the dsp file:

  $ asc2dsp t-reversed.asc t.dsp

(The TGM creation is left as an exercise for the reader.)

Now let's consider a more practical example and a real test of BRL-CAD. We can import topological (topo) data and produce a realistic ground surface.  There are many free sources of such data, but these, for US topo data, seem to be the most likely:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

We can view the SDTS data files with a free viewer (for Windows only) available here:

 

 

In order to manipulate the data in SDTS files we used the [http://gdal.org/ GDAL library] and then created a C++ program called 'sdtsdem2asc' which can be found here:

 

https://github.com/tbrowder/brlcad-usgs-topo-tools

 

After building and installing that program, we can change directory to the desired data set and create the dsp. We enter the desired base name of the image (we choose the unique data set base name)  and use the '--chop' option to minimize the dsp's vertical height to the default one meter below the lowest height in the data set.  Note the program will do all the work for us with the options shown:

 

  $ cd /path/to/3818122.dem

 

 

[[Image:381822-az35-el25.png]]