Geoscience Reference
In-Depth Information
or the free Blender sot ware available at
http://www.blender.org
h ese tools (as well as others) can be used to convert the VRML format
into other 3D graphics object i le formats such as the Universal 3D .u3d
and COLLADA .dae formats. As an example the U3D format is the format
required to place a 3D graphics object onto a PDF page with Adobe Acrobat.
h e DAE format is used to include 3D graphics objects in Apple iBooks
Author i les, for use with Apple iPads and other iOS devices with touch
controls.
h e digital terrain models created in previous sections are great examples
for such interactive 3D objects. We use a modii ed script to import and
display an SRTM data set from the previous section as an example. h e data
are imported into the workspace using
clear
fid = fopen('S01E036.hgt','r');
SRTM = fread(fid,[1201,inf],'int16','b');
fclose(fid);
h e matrix i rst needs to be transposed and l ipped vertically.
SRTM = SRTM'; SRTM = flipud(SRTM);
h e SRTM data contain numerous gaps that might cause spurious ef ects
during statistical analysis or when displaying the digital elevation model in a
graph. We can use the method described in the previous section to eliminate
the gaps. In this case, however, we have to search the data set for additional
possible NaN s, even at er having searched for NaN s and replaced them with the
means of the surrounding pixels, because the VRML clients cannot handle
the character string NaN and therefore produces an error message when
importing the i le into sot ware such as MeshLab. Since it is for display only
we can also use a simplii ed method of replacing the gaps marked by -32768
with the mean of the entire DEM.
SRTM(find(SRTM == -32768)) = mean(SRTM(:));
A coordinate system can then be dei ned using the information that the
lower-let corner is s01e036 . h e resolution is 3 arc seconds, corresponding
to 1/1,200 of a degree.
[LON,LAT] = meshgrid(36:1/1200:37,-1:1/1200:0);
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