[QGIS-Developer] Geodesic Measure Tool With Bearing Information

Nyall Dawson nyall.dawson at gmail.com
Mon Jun 12 01:27:59 PDT 2017

On 10 June 2017 at 02:30, C Hamilton <adenaculture at gmail.com> wrote:
> Several weeks ago I had proposed a geodesic measure tool that also includes
> the bearing from point A to B and bearing from B to A. Nyall suggested that
> this capability be added to the QGIS measure tool. The question is would you
> want this with the QGIS measure tool or should it be a separate plugin?

My strong vote would be towards extending the QGIS measure tool. To me
that's a better solution then requiring users to download a plugin,
and having to reimplement all the (complex) logic of the measure tool
again in a python plugin.

> 1. Where the current measure tool has 'Segments' there would be two more
> columns with 'Bearing to' and 'Bearing from'.

Sounds good!

> 2. I would like to see a check box or selection widget of some sort that
> chooses between using Geodesic math or the current method of calculating the
> distances which I am still unsure on how it is doing its calculations.

If you expand down the info box you'll get a detailed description of
exactly how QGIS is calculating the distances. Is there something
missing there?

> Right now it could use the Vincinty algorithms in QGIS to calculate the
> distances, but eventually I would like to see the geographiclib algorithms
> used.

I'd start with the bearing changes (since they are self contained, and
the methods for calculating bearing are already present in the QGIS
api). Then using geographiclib could be discussed as a separate set of
changes, to be decided on its own merit. If you mix these two changes
it's likely to get bogged down as one or other part of the changes are

> If this is of interest then I will attempt to get a QGIS development
> environment running to help make the changes to the core measure tool;
> otherwise, I will just create a plugin to do this. If I create a plugin I
> will use the geographiclib python library to do the calculations.
> Thoughts?

Go the core! Let us know if you need help setting up a dev
environment. It's actually much easier for 3.0 then it was for 2.x
(especially on windows).


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