[GRASS-user] grass : how to do Isochrone maps?

[Moritz Lennert]

On 26/02/15 00:15, image93 wrote:
> Dear all, dear Moritz,
>
> thank you again for your last usefull messages. Regarding my driving
> isochrone works. Last time (December 2014), when i executed the v.isochrones
> process, an error message appeared due to running of memory.
>
> For remind, i 'm working on windows 7 with grass 7.0. The vector network
> comes from OSM data ('roads cover). This is a big road network (490 lines
> objects!!) with of course the usefull field for speed profile. My area of
> interest is componed by the two french admnistrative regions (Ile de France
> and Picardie).

I imagine you are lacking a few zeroes here. 490 lines is not a big 
network ;-)

>
> ----------------------------------------------------------------------------
> (Wed Feb 25 22:46:55 2015)
> v.isochrones --overwrite map=roads_merge_idf_picardie_L93 at dataset layer=1
> speed_column=speed_prof start_points=MANUTAN_starting_points_L93 at dataset
> isochrones=polygons timemap=raster time_steps=15,30,45 offroad_speed=0

>    File "C:\Users\laurent\AppData\Roaming\GRASS7\addons/scrip
> ts/v.isochrones.py", line 158, in main
>      null_value = resolution / (float(offroad_speed) * 1000 /
> 3600)
> ZeroDivisionError: float division by zero

Yes, I forgot to foresee the case where the user wants an offroad speed 
of 0. For now, could you just put this to a very low value > 0 ?

Actually, what you seem to want is more like what I started to implement 
in the alternative method, i.e. v.net.iso + r.grow.distance in which 
every pixel is just assigned to the travel time of the closest network 
segment, within a user-defined distance threshold to the network (thus 
potentially allowing empty areas not covered by isochrones).

>
> I'm realy sorry to disturb you. But isochrony maps is really important my my
> project.

I'll try to find some time soon to update the module with the second method.

Moritz