hills
A program to generate 3D models of places on the Earth's surface.
It uses as input the SRTM 90m elevation data from CGIAR-CSI, which is
downloadable free of charge from http://srtm.csi.cgiar.org. It
outputs binary STL.
In spite of its name the program also works on valleys.
-- David Fletcher david@bubblycloud.com
Basic use
Pick a latitude and longitude. (Google Maps will show it when you
click on a point.)
Run hills. It won't work because we don't have the input data yet,
but it will tell us which tiles we need.
hills --position 56.64,-4.91 out.stl
Obtain the input data tiles from CGIAR-CSI
http://srtm.csi.cgiar.org/srtmdata/ or a mirror.
You want 5x5 degree tiles in the ASCII format. The download interface
on the website is better than it used to be but it still might be
quicker just to construct URLs directly like
wget http://srtm.csi.cgiar.org/wp-content/uploads/files/srtm_5x5/ascii/srtm_36_01.zip
Unzip the downloaded file and you should obtain a file named
srtm_36_01.asc.
Run hills to generate a model.
hills --position 56.64,-4.91 out.stl
Look at the output in your favourite STL viewer.
Options
--position LAT,LONG
-p LAT,LONG
Latitude and longitude as decimals. North of the equator is positive,
south is negative. East from Greenwich is positive, west is negative.
Usually the centre of the area to be modelled (but see --offset).
--dimensions ARCSECxARCSEC
-d ARCSECxARCSEC
Size of the area to model in arcseconds, latitude first. Defaults to
300x600.
Remember as you go further north or south from the equator, arcseconds
of longitude get smaller.
--base-altitude METRES
-b METRES
The bottom of the volume to be modelled. Defaults to 0m (sea level).
If you are modelling land on a plateau or massif you may want to set
this higher so that your model won't be on such a thick base. If you
are modelling land that goes below sea level you'll need to use a
negative value to put the base low enough.
--scale FACTOR
-s FACTOR
Defaults to 100, meaning 1:100. This might seem like a larger scale
than anyone would want, but note that the program outputs in metres
whereas 3D printers commonly expect millimetres, so you might already
be getting a factor of 1000 on top of what you specify here.
--input-dir DIR
-i DIR
If you have your .asc files somewhere other than the current
directory, point to them with this option.
--offset ARCSECxARCSEC
-o ARCSECxARCSEC
In arcseconds, latitude first. Offset from the specified position to
the southwest corner of the area. By default the position is the
centre of the area. So if you'd rather specify the southwest corner
you can use an offset of 0x0.
However, the main reason for this option is to generate multi-part
models without having to change the reference position. This is
convenient because the dimensions are in arcseconds so it's easier to
do your local positioning in arcseconds too. It's also more accurate,
because the program calculates the number of metres per arcsecond at
the specified position, and if you change the position between two of
the parts their scales may not match perfectly.
Caveats and bugs
-
The SRTM data doesn't go north or south of 60 degrees, so this
program can't help you in those areas.
-
The program doesn't yet do any interpolation between the input
samples. So the position you supply is rounded to the nearest input
sample position, and dimensions that are not multiples of three
arcseconds are expanded so that the edges are on 3-arcsecond
boundaries. If you care about the exact size of the model or you
are making a multi-part model, it is best to use offsets and
dimensions which are multiples of three.
-
Areas straddling the line 180 degrees east/west probably won't work.
If you want to model an area where this matters (perhaps in Fiji or
the Aleutians) let me know and I'll fix it.
Examples
Ben Nevis
This crosses a tile boundary - needs both srtm_35_01.asc and
srtm_36_01.asc.
hills -p 56.812,-4.99 ben-nevis.stl
Mont Blanc
Needs srtm_30_03.asc. We use a size of 500x1000 arcseconds and a base
altitude of 500m.
hills -p 45.8334,6.8650 -d 500x1000 -b 500 mont-blanc.stl
Part of the Grand Canyon
hills -p 36.13,-111.93 -d 1200x1500 -b 200 grand-canyon.stl
Mount Kilimanjaro
Needs srtm_44_13.asc.
hills -p -3.076,37.35 -d 1500x1500 -b 600 kilimanjaro.stl
Ochil hills
A 1:50000 scale model covering an area about 26km x 13km, in eight
parts each about 13cm x 13cm.
hills -p 56.145,-3.96 -s 50 -d 210x375 --offset 0,0 ochils-a0.stl
hills -p 56.145,-3.96 -s 50 -d 210x375 --offset 0,375 ochils-a1.stl
hills -p 56.145,-3.96 -s 50 -d 210x375 --offset 0,750 ochils-a2.stl
hills -p 56.145,-3.96 -s 50 -d 210x375 --offset 0,1125 ochils-a3.stl
hills -p 56.145,-3.96 -s 50 -d 210x375 --offset 210,0 ochils-b0.stl
hills -p 56.145,-3.96 -s 50 -d 210x375 --offset 210,375 ochils-b1.stl
hills -p 56.145,-3.96 -s 50 -d 210x375 --offset 210,750 ochils-b2.stl
hills -p 56.145,-3.96 -s 50 -d 210x375 --offset 210,1125 ochils-b3.stl
The parts are laid out like this:
b0 b1 b2 b3
a0 a1 a2 a3
