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
[email protected]
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
<[email protected]> 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:[email protected]
Web:www.nortekresources.com
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