[ gpsdrive ] GPSdrive SVN, Mapnik and a Patch

Mark Wilkinson mark.wilkinson at 2pmtech.com
Thu May 29 05:03:54 AKDT 2008


Hi Jannis
   thanks for the information...

Jannis Achstetter wrote:
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> Guenther Meyer schrieb:
> | Am Donnerstag 29 Mai 2008 schrieb Mark Wilkinson:
> |>> I'm not sure how to measure this... it was enough to throw my location
> |>> in plymouth UK, several miles into the english channel.. guess i'm
> |>> gonna have to figure it out now :-)
> |> It seems to be approx  11' 19.61"  south
> |>
> I once had exactly the same problem. I used the osm2pgsql-tool from OSM
> to import the .osm-file to the database without the "-m" switch an
> gpsdrive worked but the mapnik-scripts from OSM ("generate_image.py"),
> didn't work correctly. Then I imported once again with the -m switch and
> then the scripts worked but gpsdrive showed me a map about 25 km south
> of my actual position. (I was at exactly 50°N and gpsdrive showed me the
> map of 49.8°N).
>   
Interesting, looking at the commands I used to import the osm data, I 
also used the -m switch
which aparently imports the data 'in proper spherical mercator not OSM merc'

this is not something i'd noticed when following the osm mapnik how-to

Looking at the code for osm2pgsql, leaving off the -m switch and using 
the original gpsdrive projection of '+proj=merc +datum=WGS84' would
probably have worked correctly, however with the how-to saying to import 
with -m, this might account for the difference of about .2 of a degree

> Then I changed the projection-definition somewhere in
> /usr/share/gpsdrive to match what the OSM-scripts used and since then
> both work
>
> Jannis
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>
>   
Mark.


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