[GRASS-user] new earthquakes demo

Hamish hamish_b at yahoo.com
Tue Dec 21 19:04:14 EST 2010


I have taken Markus's PHP earthquake demo[1] and set it up as a nightly 
refresh job on one of the OSGeo servers[2]. A few things still to improve,
but a demo of what can be done; most importantly the magnitude is now
logarithmic instead of linear as it is usually presented. It's scaled back
from the true nature of the energy (magnitude is not simply log10, it's a
lot more than that), but doing it more accurately would mean the really big
ones would be off the page (see the legend[3]). I'm expect to have the
polished version in the Winkel Tripel projection[4]; I tried Mollweide[5]
but I think that squashes the population centers of Europe and North
America when the focus is on the Pacific's "ring of fire". Backdrop is
the colorized ETOPO1 dataset[6]. As a top-end example, March's Chilean
quake was run trough it[7].

compare the large earthquake south of Japan today and Iran yesterday
represented as linear (php) scaling and the log scaling (2,4 below).

[1] http://grass.fbk.eu/spearfish/php_grass_earthquakes.php
[2] http://adhoc.osgeo.osuosl.org/grass/
[3] http://adhoc.osgeo.osuosl.org/grass/earthquake_legend.png
[4] http://adhoc.osgeo.osuosl.org/grass/alternate_projections/earthquakes_wintri.png
[5] http://adhoc.osgeo.osuosl.org/grass/alternate_projections/mollweide_155E.png
[6] Winkel Tripel is a one-way projection, so v.proj had to be used on
the RGB layer cells instead of r.proj.
[7] http://adhoc.osgeo.osuosl.org/grass/archive/earthquakes_1March2010.png

Still to improve:
- 6.4's d.vect circle symbols are a bit blocky and have line breaks
- Not sure how to implement anti-aliasing for the rings
- cairo driver not possible as this was built using GRASS_BATCH_JOB
on a headless server with no X11. (or that is to say I'd have to install
X just for it, which I don't really want to do. Even then, the huge circle
symbol looks even more blocky (again, this is 6.4.0).
- document the process and upload the scripts as a demo to the addons svn.
- v.proj for 14 million points exposed a few problems. memory leak in
v.out.ascii? the number of features from v.build needs another padding,
it doesn't delete the leading "1" when the number is bigger than 10 million.
- fix logo overlay for WinTri projection

ho ho,


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