On 02.11.20 13:57, Fernando M. Roxo da Motta wrote:
On Sun, 1 Nov 2020 17:26:46 -0500, Garth Fletcher <ga...@jacqcad.com>
wrote:
Just a side note.
If I understand it correct, this procedure will store in attribute
table (as a temporary or permanent attribute) the coordinates as they
are at the time it is stored. If a point is moved through edition that
value will not be updated automatically. It will be necessary to store
the new value in the table with the described procedure.
Yes and no: Since a while, it is possible to update values based on such
a function after doing some configurations.
First create your x and y fields and apply the $x and $y functions on
them through the field calculator.
When you now want them to automatically update on changes, go to
Layer Properties -> Attributes Form -> Pick the field in question ->
Section "Default Values" -> enter the function into the "Default value"
and tick the "Apply default value on update"
Done ;)
My experience is with .gpx files generated by a Garmin eTrex-20.
When I use QGIS's Data Source Manager to open a and Add a .gxp file I
see several different layers:
Tracks
Track Points
Routes
Route Points
Waypoints
The one you want is "Track Points" because it contains all the
individual points which collectively make up the tracks. "Tracks"
only contains link(s) to the various tracks that have been recorded -
it usually only contains one item unless you have saved multiple
tracks.
You may also be interested in "Waypoints" if you've recorded specific
waypoints on your GPS.
So Add the layers of interest (Track Points and maybe Waypoints)
Because a .gpx file is "input only", your first step needs to be to
to right-click on the layer, select Export > Save Features As...
This will let you save the layer in a form that can be edited. Keep
this new layer (you can remove the original .gpx layer)
The layer's Attribute Table contains fields for all sorts of
attributes, but NOT including the location (Lat,Long) data which is
stored separately.
So to be able to make your own location based calculations you want to
copy the point locations into new fields in the Attribute Table.
With the layer selected, select the Field Calculator (Abaccus icon in
toolbar)
check Create a new field
enter a name, e.g., "Latid"
set Output field type to Decimal number (real)
set Output field length to 10, Precision to 6
type "$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 <jimimc...@gmail.com
<mailto:jimimc...@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
<ga...@jacqcad.com <mailto:ga...@jacqcad.com>> wrote:
On 10 Sep 2020 at 20:12, J. M <jimimc...@gmail.com
<mailto:jimimc...@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
Roxo
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