Editing DSP
From BRL-CAD
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Example 1. | Example 1. | ||
− | In | + | In mged create a dsp object: |
mged> in dsp1.s dsp f Ex1.dsp 142 150 0 ad 1 0.005 | mged> in dsp1.s dsp f Ex1.dsp 142 150 0 ad 1 0.005 | ||
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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). | 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. | |
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− | For example, let's create the letter | ||
$ cat t-normal.asc | $ cat t-normal.asc | ||
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Now reverse the file: | Now reverse the file: | ||
− | $ tac t-normal.asc > t | + | $ tac t-normal.asc > t.asc |
and see the result in perfect form for asc2dsp: | and see the result in perfect form for asc2dsp: | ||
− | $ cat t | + | $ cat t.asc |
0 0 1 0 0 | 0 0 1 0 0 | ||
0 0 1 0 0 | 0 0 1 0 0 | ||
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Finally, create the dsp file: | Finally, create the dsp file: | ||
− | $ asc2dsp t | + | $ asc2dsp t.asc t.sp |
(The TGM creation is left as an exercise for the reader.) | (The TGM creation is left as an exercise for the reader.) | ||
− | === A practical example | + | === A practical example === |
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− | + | Now let's consider a more practical example and a real test of BRL-CAD. We can import topological data and produce a realistic ground surface. There are many free sources of such data. See this site for a start: | |
− | + | http://www.naturalgfx.com/free_topo_gis.htm | |
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− | + | We started with shapefile data for the US from: | |
− | + | http://seamless.usgs.gov/data_availability.php?serviceid=Dataset_19 | |
− | + | We downloaded the zip archive 'ned_19_arc.zip' and unzipped in its own directory: | |
− | $ mkdir | + | $ mkdir ned_19_usa_arcgis_shapefile |
− | ... | + | $ mv ned_19_arc.zip ned_19_usa_arcgis_shapefile |
+ | $ cd ned_19_usa_arcgis_shapefile | ||
+ | $ unzip ned_19_arc.zip | ||
+ | Archive: ned_19_arc.zip | ||
+ | inflating: ned_19_arc.dbf | ||
+ | inflating: ned_19_arc.pdf | ||
+ | inflating: ned_19_arc.prj | ||
+ | inflating: ned_19_arc.sbn | ||
+ | inflating: ned_19_arc.sbx | ||
+ | inflating: ned_19_arc.shp | ||
+ | inflating: ned_19_arc.shp.xml | ||
+ | inflating: ned_19_arc.shx | ||
+ | inflating: ned_19_arc.txt | ||
+ | inflating: ned_19_arc.xml | ||
+ | inflating: NED_DataDictionary2006.pdf | ||
− | + | See these pages for details of the [ESRI] shapefile format: | |
− | + | http://en.wikipedia.org/wiki/Shapefile | |
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− | + | http://www.esri.com/library/whitepapers/pdfs/shapefile.pdf | |
− | + | Before we can create the dsp for the topo data we will have to extract the data we want and get it in shape to use. We will use the open source Geospatial Data Abstraction Library (GDAL) and its OGR subset to create a C++ program to manipulate the shapefile data. The library and documentation are available here: | |
− | + | http://gdal.org | |
− | + | We will also use the nanoflann header-only library to help transform the contour data, which is not gridded, into gridded data. That library is available here: | |
− | + | http://code.google.com/p/nanoflann/ | |
− | + | Our program will be made available in the BRL-CAD package. | |
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− | + | ==== Strategy ==== | |
− | [ | + | [TO BE CONTINUED] |