[Qgis-user] GPX data in QGIS.

[Garth Fletcher]

My experience is with .gpx files generated by a Garmin eTrex-20.

When I use QGIS's Data Source Manager to open a and Add a .gxp file I
see several different layers:
  Tracks
  Track Points
  Routes
  Route Points
  Waypoints

The one you want is "Track Points" because it contains all the
individual points which collectively make up the tracks. "Tracks"
only contains link(s) to the various tracks that have been recorded -
it usually only contains one item unless you have saved multiple tracks.

You may also be interested in "Waypoints" if you've recorded specific
waypoints on your GPS.

So Add the layers of interest (Track Points and maybe Waypoints)

Because a .gpx file is "input only", your first step needs to be to
to right-click on the layer, select Export > Save Features As...

This will let you save the layer in a form that can be edited. Keep
this new layer (you can remove the original .gpx layer)

The layer's Attribute Table contains fields for all sorts of attributes,
but NOT including the location (Lat,Long) data which is stored
separately.

So to be able to make your own location based calculations you want to
copy the point locations into new fields in the Attribute Table.

With the layer selected, select the Field Calculator (Abaccus icon in
toolbar)
  check Create a new field
  enter a name, e.g., "Latid"
  set Output field type to Decimal number (real)
  set Output field length to 10, Precision to 6
  type "$y" in the Expression window below
    {$y is the location's Y axis, i.e., its latitude}
  click OK
the first time it may warn you that the layer is not in edit mode and
than proceding will turn on edit mode - this is fine

Now repeat for a 2nd field, using a different field name and expression
   "Longid" and $x

Now when you open the layer's Attribute Table you will see 2 new fields
at the right which contain the point's Latid and Longid values...

Save the layer if you want to keep these additions.


On 11/1/20 2:17 PM, J. M wrote:
> Hi again Garth,
> 
> Well I parked this problem and only just came back to it. I may have 
> missed something, but when I create the new fields you suggested in the 
> Track they contain no information. Is this a very advanced procedure? It 
> seems like something quite basic, but perhaps I've underestimated it (as 
> I usually do with QGIS!).
> 
> Kind regards,
> Jimi.
> 
> On Fri, Sep 11, 2020 at 11:51 AM J. M <jimimckay at gmail.com 
> <mailto:jimimckay at gmail.com>> wrote:
> 
>     Hi Garth,
> 
>     Thanks a lot for the very complete answer! I'll give it a go as soon
>     as I resolve an unrelated Ubuntu problem. I hadn't realised that GPX
>     data wasn't automatically visible in Properties, and that fields had
>     to be created.
> 
>     Kind regards,
>     Jimi.
> 
>     On Fri, Sep 11, 2020 at 4:26 AM Garth Fletcher <garth at jacqcad.com
>     <mailto:garth at jacqcad.com>> wrote:
> 
>         On 10 Sep 2020 at 20:12, J. M <jimimckay at gmail.com
>         <mailto:jimimckay at gmail.com>> wrote:
>          > I can successfully import .gpx files into QGIS, and they are
>         visible and
>          > can be clustered in new groups (waypoints, tracks and routes
>         appear as
>          > independent layers). The problem I'm having is that I can't
>         seem to find
>          > any way to access the data about the routes (distance, time,
>         etc) which is
>          > clearly visible in the app I used to create the tracks
> 
>         The GPX file contains a number of fields whose contents you can
>         see /
>         access in the layer's Attribute Table
>            right-click on layer and choose Open Attribute Table
> 
>         However, these are only the extra fields in the GPX records but
>         NOT including the x,y coordinates (Long,Lat)
> 
>         To access the later, use the Field Calculator
>            select the layer
>            click on Open Field Calculator icon (Abaccus) in the menu bar
>               which is next to the Open Attribute Table icon in menu, or
>             in Processing > GDAL > Vector Table > Field Calculator
> 
>         create new fields, called Lat and Long, as decimal numbers
>         and enter the expression $X or $Y (see Geometry > for details)
>         When you click OK, the new fields will be appended and filled in
>         with the right values.
> 
>         You can then access them in the layer's Attribute Table.
> 
>         With those 2 extra fields you essentially have access to everything
>         that was recorded in the GPX file.
> 
>         You can also use Field Calculator to add more fields and populate
>         them with calculation results.
> 
>         As an aside, Field Calculator cannot create new fields in the GPX
>         file; instead it creates them as temporary virtual fields.
> 
>         A better approach is to first save the data in a shape file
>            right-click on layer, choose Export > Save selected features
>         then open that file instead of the original GPX.
>         Field Calculator will add new fields to that format.
> 
>         Cordially,
>         -- 
>         Garth Fletcher

-- 
Garth Fletcher, President, JacqCAD International
288 Marcel Road, Mason, NH 03048-4704
(603) 878-4749
JacqCAD MASTER website: www.JacqCAD.com