[Qgis-user] Add distance to shapefile M

[Stewart Holt]

I do volunteer GIS work for an organization which maintains the Georgia
part of the Appalachian Trail. Given that the trail climbs over mountains,
elevation and distance are important data.  In the early days I developed a
large number of Perl scripts to do things like lookup elevation and
calculate 3D distance to create a PolyLineZM shapefile from collected data.
I have used QGIS for 6 or 7 years but mostly for making maps and organizing
data. I am now in the process of switching the remaining workflow to QGIS
so that others can do the work. The Drape function serves the need of
adding LIDAR based elevation but I am still reliant on a Perl script to
calculate the cumulative distance to put on each point of the line. I have
not been able to find any tool or plugin in QGIS to do this. Please let me
know if there is one.

If not...

I was a software developer for 43 years and have used Python for several
things. The recent Friday talk on plugins has inspired me. If there is no
alternative, I would like to create a plugin to calculate and add the 3D
distance to a PolylineZM shapefile. The data is all in Geo coordinates so I
would need to use a QGIS method to calculate the 2D distance. I would have
an option to use cartesian coordinates as well. The Drape function is
exactly the interface that would work well. This function could be added as
an option to Drape, but I think it is native code. I am not afraid of C++
but have not set up a development environment.

If a new plugin is the best approach, I would start with someone's existing
plugin which uses a layer as input, does something with it, and saves it to
a new layer. I would also need to find the method to calculate geo
distance. Any help in getting started would be greatly appreciated.

Stewart Holt
Georgia Appalachian Trail Club
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