[OSM-talk] GPS point density map? (Was: Free the postcode maps)

[Christopher Schmidt]

On Wed, Jul 05, 2006 at 10:44:52AM +0100, Nick Black wrote:
> On 7/4/06, Petter Reinholdtsen <pere at hungry.com> wrote:
> >
> >[Nick Black]
> >> This isn't strictly OSM, but as FTP is a sister project I thought
> >> I'd bug you guys anyway.  I've made a quick density map of the
> >> current FTP database, which can be found here:
> >
> >What about making a density map of the GPX files uploaded into OSM?
> >It would be fun to know where the most points are submitted. :)
> 
> 
> 
> My guess - London.  I'll take a look.  I've been making these maps in
> ArcGIS, but I'd like to start using GRASS a lot more.  Has anyone imported
> the OSM XML into GRASS?

Yep.

> What would also be interesting would be to interpolate the points, set a
> threshold, and see how the thresholded surface compares to the lines formed
> by segments and ways.  Before I start doing this has anyone tried it before?

Yep. Some documentation on the wiki:

http://wiki.openstreetmap.org/index.php/Simplifying_OSM_Shapefiles

$THRESH in this case is a threshold value for simplification.

The 'minscales' where these threshold values were indistinguishable from
the underlying map were:

osm_semgent_0.01: 3,000,000
osm_segment_0.005: 750,000
osm_segment_0.001: 200,000
osm_segment_0.005: 50,000
osm_segment_0.0001: 20,000

The approximate line counts moved in a mostly linear fashion from 20,000
to 90,000.

http://wiki.openstreetmap.org/index.php/Converting_OSM_to_GML should let
you convert to GML, and from there to something like a shapefile, which
I think you can then load into GRASS.

(I did this all 4 months ago, so my memory may be hazy.)

-- 
Christopher Schmidt
Web Developer