[ gpsdrive ] Map formats

Hamish hamish_nospam at yahoo.com
Tue Sep 11 18:57:27 AKDT 2007


> Bernhard Rohrer wrote:
> > I am new to this list and am looking at using this program for
> > navigating a boat. My main question si whether pre-calibrated maps are
> > beign supported like for instance BSB.

not yet, hopefully gpsdrive will get full GDAL support one day. This is
planned.

Ryan J. Earley wrote:
> Georeferenced maps are not _directly_ supported, but can easily be
> imported through a utility like Hamish Bowman's gdal_slice.sh,
> available at the bottom of this page:
> http://hamish.bowman.googlepages.com/gpsdrivefiles

oops, I still need to apply a couple new updates to that.
 
> This should take any georeferenced format that the gdal tools can
> understand (list: http://www.gdal.org/formats_list.html) and convert
> them to tiles that gpsdrive can use.
> 
> I have used a similar method to import BSB's from NOAA before with
> success.  I seem to remember going to going BSB--> GTiff -->gpsdrive,
> (perhaps because of needing to reproject the maps)...but this may now
> be possible in one step.

Perhaps it might need slight modification, but the script should be able
to do direct BSB -> gpsdrive, as the GDAL tools can, so there shouldn't be
a need for an intermediary GeoTIFF. Mainly it is just gdalinfo and
gdal_translate in a loop. You can try those by hand. gdalinfo needs to
show the lat/lon coords of the map's corners.

some newer BSB softcharts may be encrypted, GDAL can't deal with those.


the other method which is more flexible but less direct is to load the BSB
charts into GRASS GIS (http://grass.itc.it) with the r.in.gdal module,
then export to gpsdrive tiles using the d.out.gpsdrive module.


I have noticed there is a problem when a projected (ie not lat/lon)
regional scale map is cut up for gpsdrive with the gdalslice script, as
north (up) in the projection may not be exactly in line with true north
and so the map is slightly rotated. (only for 1:200000+, 1:50000 or finer
is hard to spot) Some of my maps are perfect, others are way off. The
above north rotation is my best guess right now, but I've not fully
convinced myself of that.

So it's pretty good as a guide, but don't trust it yet to keep you away
from a rock. Having said that I use gpsdrive to steer to my sampling
stations (naut chart + waypoint overlay), and for those fine scale maps it
works great.


Hamish


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