[Qgis-user] Qchainage plugin

[Stewart Holt]

Tim,

Depending on how the GPS data was collected for the trail, your line shape
may be longer than the actual trail. Each GPS point has some error and if
the points were collected at one per second, the additional length caused
by points being off the centerline, could be significant. GPS height is
more noisy with error than the horizontal distance. That can contribute a
lot of extra length. I use a sub-meter GNSS unit and filter the points to
be no less than 10 feet apart. I add elevation from a USGS layer using the
QGIS drape function because that is more accurate than the GPS height. By
doing this, the 3D length is within about 1% as compared to a measuring
wheel.

I made the earlier post for work I do for the Appalachian Trail. What I
want is a way to calculate the 3D distance from one point to the next and
put the running total in the M value of each point. In my case, the layers
are in geo coordinates and would require the horizontal distance be
calculated with lat/lon. I read the descriptions of every plugin and
determined that nothing currently does what I wanted. I am a programmer but
have very little Python experience. I did get one response which was
helpful in writing plugins but have not yet pursued it. An example of a
plugin which takes a vector layer input, does something (or nothing) with
it and creates an output layer would be a good starting point. If I can
achieve what I want to do, what you need would be a simple change.

Stewart Holt
Georgia Appalachian Trail Club


On Thu, Mar 30, 2023 at 3:10 PM Tim Fearn via QGIS-User <
qgis-user at lists.osgeo.org> wrote:

> Hi everyone,
> I’m trying to use the qchainage plugin to create ½ mile markers along a
> vector line that represents a trail.  The line is a single feature with no
> multi-parts or dangles.  It is about 318 miles long so I would expect right
> around 636 points if there is one every half mile.  My project default is
> set to miles for length measurements as is the qgis main preference.  I set
> the unit measurement to miles and input .5 as the interval.  I continually
> get 771 points instead of the expected 636.  Also when I use the automatic
> labeling feature of the plugin it appears to be in degrees not an aggregate
> mileage.
>
>      Several weeks ago a fellow had queried the list on the same subject.
> He was working with the Appalachian Trail I believe and wanted to place
> points at given distances.  No one seemed to really understand so I’m
> hoping that if anyone remembers the original poster, and has come up with
> any thoughts or other ideas it would be much appreciated.  This is
> something that can be done for sure.  All of the National Scenic Trail maps
> in this country are demarcated with some form of mile or half mile makers
> which when labeled show the accumulated distance.
>
>      Hoping for some traction on this.  I’ve only just started learning
> python so I wouldn’t describe myself as a programer and am looking for a
> relatively simple solution.
>
> With much gratitude,
>
> Tim Fearn
> _______________________________________________
> QGIS-User mailing list
> QGIS-User at lists.osgeo.org
> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-user/attachments/20230330/82707e07/attachment.htm>