[Qgis-user] Converting or rendering GPS track points as line but preserving point data

[pcreso at pcreso.com]

Hi Nathaniel,

This is a data management issue, not a rendering one.  

You need to break up your track LINESTRING by splitting at the points into separate LINESTRINGS - where each successive pair of points are joined to make a separate feature.  

Each LINESTRING feature can then be given a Z value which can be used to colour it.

So your GPS track becomes a series of two-point lines instead of a single multi point LINESTRING.

Hope this makes sense... 

Brent Wood

--- On Fri, 4/19/13, Nathanael Boehm <nboehm at purecaffeine.com> wrote:

From: Nathanael Boehm <nboehm at purecaffeine.com>
Subject: Re: [Qgis-user] Converting or rendering GPS track points as line but preserving point data
To: qgis-user at lists.osgeo.org
Date: Friday, April 19, 2013, 3:19 PM

This is pretty much the outcome I'm after, but I've fudged this by making the data points big enough to overlap and then faux masking what hangs over the underlying track polyline by setting the blending mode so that anything over white is invisible, and also tweaking the rendering passes so that lower elevation data points get rendering precedence.


http://twitpic.com/ckbrdt

If that's the only way it can be done I guess I can live with that, although will cause problems when I want to show topography etc. Also misrepresents the data due to the points being rendered more like polygons, with a 5mm size.


Cheers,

Nathanael Boehm
UX designer specialising in business web & mobile apps

www.purecaffeine.com

Canberra, Australia



On Fri, Apr 19, 2013 at 12:06 PM, Nathanael Boehm <nboehm at purecaffeine.com> wrote:


I promise not to spam the mailing list, but I do have another question I'm hoping someone can help with.
In other GPS software like ExpertGPS or the online GPSVisualizer you can style a GPS track based on track point attributes like elevation or timestamp etc.



However when you import GPS or GPX data into QGIS (either as a new vector layer or using the vector tools and GPS plugin) it treats the track points and track line as separate layers … and the line is pretty useless except for visually connecting the dots, but it has no data associated with it.



This is a GPS track in QGIS with a graduated classified style applied on the elevation "ele" attribute of the track points:
http://twitpic.com/ckbe47




I would like to render this as a line but still have access to all 250+ vertices in order to apply styling like I have above (but as a line instead of 250+ individual points as it's kind of ugly)



Is it possible? I've tried Point2One with no success. All I've managed so far is to add the geometry columns to the track points layer, but that doesn't help with creating the polyline.



Cheers,

Nathanael Boehm
UX designer specialising in business web & mobile apps

www.purecaffeine.com

Canberra, Australia





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