[GRASS-user] Re: How to draw the earthquake-magtintude map...

[Hamish]

Yasuo shimada wrote:
> I wish to express my gratitude to your some advices. 
> 
> I understood the command that drew in circle. 
> Also, I understood the magnitude was not simple.
> 
> It explains the process...:
> 
> (1)
> d.vect.thematic map=quake column=mag type=point
>   themetype=graduated_points icon=basic/circle
> 
> ...It succeeded.
> 
> (2)
> d.vect map=quake size_column=mag icon=basic/circle
> ...error message "Sorry, <size_column> is not a valid
> parameter"

ah, what version of GRASS are you using? that option is new for
GRASS 6.4.1. (also the rotation column option)

 
> (3)
> d.vect map=quake size=mag icon=basic/circle
> ...It succeeded. but very small symbolsize...

size= should only accept a number, the default size= is 5.0,
which is quite small.  For some reason the parser doesn't
complain that you gave it a string.


> (4)
> d.vect map=quake size=10^(11+1.5*mag) icon=basic/circle
> ...error message "token (' syntax error..."... 
> Why ?

size= is not that smart (yet), but it's a rather good idea!
it just takes a single number.
I am not sure if the "token" error comes from your terminal
shell (needs quoting) or from GRASS (doesn't support that), but
either way, it won't work.

> (5)
> d.vect map=quake size=10^mag icon=basic/circle
> ...It succeeded.

I suspect that atof() just scanned as far as the "10", and
then used that as a static size.


try upgrading to 6.4.1, and the size_column= option should
start to work. (n.b. adding this option was actually inspired by
the desire to vary symbol size for earthquake plots)

also you will find in GRASS 6.4.1 the new extra/ring symbol,
which is similar to basic/circle with fill_color=none, but
allows the dynamic color setting to colorize the border line,
not the fill area. (so the fill area does not mask smaller quakes
at close epicenters)


see here for method of adding a new column, containing a measure
of un-logged energy, which can then be used for the d.vect
size_column:

https://trac.osgeo.org/grass/browser/grass-promo/tutorials/batch_processing/earthquakes/do_quakes_latlon.sh#L67



Hamish