Slice and dice GridFloat files from the command line.
> wget -O ./n46w122.zip "http://gisdata.usgs.gov/TDDS/DownloadFile.php?TYPE=ned3f_zip&FNAME=n46w122.zip&ORIG=RVS"
> unzip n46w122.zip
> ./gridfloat -n 45.37344 -w 121.69566 -s 0.2 -R 512 -A 180 -P 20 -o mthood_sunset.png ./n46w122/floatn46w122_13
Boom.
Want 3D?
> ./gridfloat -n 45.37344 -w 121.69566 -s 0.2 -R 512 -o mthood3d.stl ./n46w122/floatn46w122_13
Snapshot from MeshLab:
Bam.
The following will produce the executable, gridfloat in
the repo. This program depends on libpng, readily available
from your friendly Linux distro package manager (You'll need
the development version. Currently, on Ubuntu 12.04, that is
"libpng12-dev").
> git clone https://github.com/bauerca/gridfloat.git
> cd gridfloat
> make
Grab some elevation data from The National Map Viewer by clicking on the light-blue down-arrow icon and following the instructions, making sure to check the "Elevation" box.
When it comes time to select your specific elevation product, go for the GridFloat format.
Once downloaded, unzip and check out the usage instructions below.
The following can be obtained on the command line from
./gridfloat -h:
Extract subgrids of data from a GridFloat file. GridFloat is a simple format commonly used by the USGS for packaging elevation data. A header file with geolocation metadata is required for making queries based on latitude/longitude.
gridfloat [options] FLOATFILE HEADERFILE
gridfloat [options] FLOAT_HEADER_PREFIX
where, for the first case, FLOATFILE should have extension .flt and HEADERFILE .hdr. If both HEADERFILE and FLOATFILE have the same filename prefix, then you can use the second case.
-h: Print this help message.
-i: Print helpful info derived from GridFloat header file.
-R: Resolution of extraction. If a single integer is
supplied, then the resolution is the same in both
directions. Otherwise, the format is (by example):
'-R 128x256' where the first number is the resolution
in the x-direction (along lines of latitude).
-l: Left bound for extraction.
-r: Right bound for extraction.
-b: Bottom bound for extraction.
-t: Top bound for extraction.
-B: Specify extraction bounds using a comma-separated
list of the form LEFT,RIGHT,BOTTOM,TOP. E.g.
'-B -123.112,-123.110,42.100,42.101'.
-n: Longitude midpoint of extraction. Must use with '-s'
option. Example: '-n 42'.
-w: Latitude midpoint of extraction. Must use with '-s'
option. Example: '-w 123' (notice there is no minus
sign here).
-p: Lat/Lng midpoint of extraction. Must use with '-s'
option. Example: '-p -123,42'.
-s: Size of box (in degrees) around midpoint. Used with '-p'
and '-n','-w' options. Examples: '-s 1.0x1.0' or just '-s 1'.
If a rectangular size is requested, the first number refers
to the width of the box (along x; i.e. along lines of
latitude).
-T: Transpose and invert along y before printing the array
(so that a[i, j] gives longitude increasing with i and
latitude increasing with j).
-o: Output subgrid data to a file. Detects output format based
on file extension. Supported: (.png, .stl). For a .png
extension, see "PNG output options" below. Otherwise,
gridfloat will assume you want to save another GridFloat
file. In this case, it will write the appropriate data
and header files, appending .flt and .hdr, respectively,
to the argument of -o.
When png output is specified, gridfloat automatically renders a shaded relief map. The following options determine which slopes are sunny.
-A: Azimuthal angle (in degrees) of view toward sun (for
relief shading). 0 means sun is East, 90 North, etc.
Default: 45 (NE).
-P: Polar angle (in degrees) of view toward sun (for
relief shading). 0 means sun is on horizon, 90 when
directly overhead. Default: 30.
All of the following are equivalent and simply print data to stdout.
gridfloat -l -123 -r -122 -b 42 -t 43 file.{hdr,flt}
gridfloat -B -123,-122,42,43 file.{hdr,flt}
gridfloat -p -122.5,42.5 -s 1 file.{hdr,flt}
gridfloat -w 122.5 -n 42.5 -s 1x1 file.{hdr,flt}