[Freegis-list] GPS/NMEA data processing

[Nils Faerber]

Am Do, den 10.06.2004 schrieb Bernhard Reiter um 22:42:
> On Wed, Jun 09, 2004 at 06:32:56PM +0200, Nils Faerber wrote:
> > After the quite lengthy but very informative thread about GPS/NMEA GIS
> > data processing I thought I should share my findings with you. It is not
> > much but at least something.
> No, that is great! 

Thanks ;)

> > I had a look at QGIS and Thuban now.
> > QGIS and Thuban do even look quite similar and offer similar
> > functionality - still not vector editing, i.e. you cannot modify the
> > shapes, 
> Jump probably can do more, but it does not avoid the Java trap
> (http://www.fsf.org/philosophy/java-trap.html).
> Also PostGIS might help with more complicated operations.

Yes, Java is not my choice too. Even apart from the philosophocal
reasons there might be I do not like programming with Java and
especially not the performance of the resulting program. When I startup
a program on a decent machine I do not want to wait five minutes before
it finally comes up.
Even interpreted Python is faster than Java.

If I find some additional time I'll look into PostGIS.

> > but you can add annotations and export simple maps from imported shapes. 
> The main point of an interactive geoviewer are the classification functions.
> If you want to touch up nice printing maps, you should try the
> experimental SVG writing support of Thuban (in CVS) and the Skencil
> Thuban-Map-SVG reader. Skencil is a full blown vector drawing
> application that will allow you to make nice maps and even work on
> the polygons.

Ah, cool, that sound primising!
Though I am still thinking about this GPS map creation stuff. And
involving too many application in the process will make it impossible to
collect GPS data from different sources - ideally from thousands of
users. But that's another story for later ;)

> > QGIS add the functionality of plugins, one of them a GPS import plugin.
> Thuban calls a plugin "Extension".

Ah, OK, sorry :)
Will correct that on the page.

> > Though this plugin did not work for me it pushed me into the right
> > direction of looking for a filter to change GPS/NMEA tracks into shapes.
> > After some research I found a small program called "gpstr2shp.c" which
> > converts GPS track data into shape files. 
> Good catch.
> I did look into creating a Thuban "Plugin" using gpsbabel
> which looks promissing, just needs a couple of hours work.

I looked at gpsbabel and for some reason it does not work for me in
almost all combinations I tried. Either the NMEA input is broken or I do
some other mistake, I don't know.

I think that not using gpsbabel also give the opportunity to add some
more sophisticated options to the NMEA filter.
NMEA is dumb, i.e. it knows nothing about tracks and points and
espcially not about polygons or vectors. The QGIS plugin has some nice
options (which also did not work for me but showed the idea) to tune the
filter. You could introduce thresholds for connecting waypoints to
tracks for example, i.e. if two points are not more than xx degrees
apart from each other then it can be assumed that they are on the same
track. Also is the time distance between two points is more than xx
seconds/minutes then a new track could be started, etc.

You see, this way you could just dump your NMEA data for days and have
at least somewhat intelligent shapefile output.

> > This track data is not NMEA
> > but a rather simple format. 
> gpsbabel with GPSMAN format support might help you here directly.
> Try to convert it into that.

Yes, it would ;)
But then you run into trouble that the output from NMEA input will
always, if at all (s.a.), be just waypoints and no tracks.

OK, let's correct the web page first and then look for Skencil ;)

Oh, and while we are at it, now that I finally have a shapefile I can
also try to use GRASS now ;) Real fun coming up!

> 	Bernhard
CU
  nils faerber

-- 
kernel concepts          Tel: +49-271-771091-12
Dreisbachstr. 24         Fax: +49-271-771091-19
D-57250 Netphen          Mob: +49-176-21024535
--