Hi Harrissou,
Turn out I had a float point error problem with the distance matrix tool
that indicated I had no disconnected lines in my network. The distance
matrix tool reports 0 distance when the distance is around or below the
10th decimal point. I have fixed the problem and dissolve followed by
multipart to single part does work with lines like it does with polygons
and does dissolve line ends. I will report the error on the distance
matrix tool that I was using to find my disconnected line nodes.
Thanks for your help and for insisting I figure out problem.
Nicolas
On 2021-08-31 11:20 p.m., Nicolas Cadieux wrote:
Hi,
I will look at the wkt output but it seems that with lines, dissolve
will just create a single huge multiline. The multi part to single
part will just split it back up. I suspect that dissolve only deals
with common border in polygones and not line ends. Will test tomorrow
to figure out more details.
Nicolas Cadieux
https://gitlab.com/njacadieux <https://gitlab.com/njacadieux>
Le 31 août 2021 à 03:57, DelazJ <del...@gmail.com> a écrit :
Hi,
> That does not work with lines unfortunately. I tried multiple times
with different combinations. It works with polygons when common
borders need to be dissolved.
Nicolas, can you elaborate a bit more on the issues you have with the
"Dissolve + Multipart to singleparts" solution I provided few days
ago. At which step is it failing? The dissolve does not merge joining
features into a single one? I don't know the function internals but
I'd expect it to work this way and if not, would sound like a bug to
report IMHO...
Regards,
Harrissou
Le mar. 31 août 2021 à 00:57, Nicolas Cadieux
<njacadieux.git...@gmail.com <mailto:njacadieux.git...@gmail.com>> a
écrit :
Thanks Charles,
This will be very useful. Nice to know I'am not the only one
going crazy with this!!!
Nicolas
On 2021-08-30 4:42 p.m., Charles Dixon-Paver wrote:
I thought this would be easily solved with an expression but
sadly I haven't been able to get reliable results at all.
My first thought was
collect($geometry,filter:=intersects($geometry,geometry(@parent)))
and when that didn't work I tried various aggregates and union
operations to no avail. Something like this might be useful if
you can get it into a usable form (I managed to get various
multigeometries in the form you are looking for but wasn't able
to do much with them and there seemed to be artifacts):
collect_geometries(array_foreach(aggregate(layer:='lines',aggregate:='array_agg',expression:=$geometry,filter:=intersects($geometry,geometry(@parent))),@element))
I was actually waiting for someone else to come up with a more
elegant solution, but it would probably also be possible to
identify intersecting features and get the minimum/ maximum
feature id for intersecting features with this:
aggregate(layer:='lines',
aggregate:='min',
expression:="fid",
filter:=intersects($geometry,geometry(@parent)))
You could use that in the field calculator to create a field for
"grouping" various intersecting features to dissolve on, however
it's only going to identify the minimum of the currently
intersecting features so you would need to iterate through the
process multiple times. I can't think of an effective way to
implement a "while" conditional either.
It's a pretty clanky way to do it, but if you are really
struggling I think it's possible.
On Mon, 30 Aug 2021 at 22:10, Nicolas Cadieux
<njacadieux.git...@gmail.com
<mailto:njacadieux.git...@gmail.com>> wrote:
Hi,
Seems like the plugin is available so I will try it out.
The ability to create multi-linestring out of any touching
lines (touch here means intersects at the first or last
node) would be nice to have it if I can include it in a model.
My goal is for this model to work for anyone with a basic
install of QGIS LTR or 3.20 with minimal efforts so I am
trying to eliminate the need to rely on external plugins or
scripts.
This is also my first attempt with models. It’s a learning
curve but I am having fun… I think this probably should have
been a plugin but my knowledge of GUI programming is
basically 0. That will be for a next project…
Nicolas Cadieux
https://gitlab.com/njacadieux <https://gitlab.com/njacadieux>
Le 30 août 2021 à 14:59, David Strip
<qgis-u...@stripfamily.net
<mailto:qgis-u...@stripfamily.net>> a écrit :
I looked at the source for this plug-in and as far as I
can tell it only merges lines that meet at endpoints. It
ignores multi-lines, and only creates linestrings, so there
are no vertices of degree >2 (ie, no junctions/forks).
Also, the plug-in doesn't look for intersections between
vertices (since it only looks to merge endpoints.)
The StackExchange post appears to want multi-linestrings,
which gives forks and such. Is that what you need?
On 8/30/2021 5:27 AM, Nicolas Cadieux wrote:
Hi,
This is the plugin I was referring to. I don’t see it in
the current plugins (experimental turned on) so I figured
it’s QGIS 2 only.
https://github.com/ArMoraer/QGISMergeLines
<https://github.com/ArMoraer/QGISMergeLines>
Nicolas Cadieux
https://gitlab.com/njacadieux <https://gitlab.com/njacadieux>
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