[Qgis-user] Qchainage plugin

[Kirk Schmidt]

Hi Stewart:

You could write a simple script using python or modeler to do what you 
are looking for.  I would reproject to a UTM or similar projection and 
then the math for each segment gets easier.

Reach out to me privately as I have some ideas on how to implement it.

Kirk Schmidt

kirk at nortekresources.com

On 3/30/2023 4:56 PM, Stewart Holt via QGIS-User wrote:
> 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
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-- 
Kirk Schmidt, MScF, BScF, RPF
General Manager
Nortek Resource Solutions Inc.
26 Church Road
Sutherlands River, NS
B0K 1W0
Tel (902) 922.3607
Email:kirk at nortekresources.com
Web:www.nortekresources.com
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