Hi Régis,

I do not quite understand what you mean with the m or z picker tool, however I have some Python code here in operation that returns a "station" on a line by clicking on the line (or near it, as you won't hit the line without snapping to segment). A "station" is a position on the line, i.e. the start point of the line is station = 0, the end point of the line is station = line.length(). Rational was to identify stations on street lines where certain infrastructure like sewer covers are situated.
Will share if you are interested.

regards

Bernhard

Am 07.09.2016 um 21:22 schrieb Régis Haubourg:
Hi All,
I've been using linear referencing extensively here to produce european
reference datasets of water bodies. Postgis works just fine and fast.
What I have been missing, and average users probably miss that too, is:

  - A tool to "calibrate" a route from data, points, or lines:
Currently LRS can do that only with point data. Postgis misses also a
simplified function.
  That "route generation" tool should have tolerance options and do
something like a grass clean and auto arc orienting, and must be able to
generate route from points or lines, or multilines.


- A generic graphical "m" or "z" picker editor widget:
Use case: you need to create linear or point events against a route system,
just clicking on a route and getting X,Y, M,Y and storing it in attribute
table . I can imagine along the line edit widget, a small button (like a
color picker) , once pressed allow the user to click on the map. Question
is, how to confirm wich geometry event has been clicked in case of
proximity or superposition. One idea could be to have a dropdown list box
of values under the click, displaying event identifier and m / z value.

I'd be happy to discuss that with you all.


Cheers
Régis



2016-09-07 16:51 GMT+02:00 Neumann, Andreas <a.neum...@carto.net>:

Hi,

Yes, I know about LR expressions in the current master versions.

So one could visualize the events table through a virtual geometry column
- would that work?

I will forward all this information to my friend.

Greetings,

Andreas

On 2016-09-07 15:34, Matthias Kuhn wrote:

Hi Andreas,

In QGIS 2.18 / QGIS 3.0 this should be possible via expressions:

https://github.com/qgis/QGIS/commit/e110ba7d54b0ac7d3f63e8ed7eaebb
2845f9f38c

Best regards
Matthias

On 09/07/2016 02:24 PM, Neumann, Andreas wrote:

Hi,

A friend of mine asked me if QGIS can do linear referencing - e.g.
symbolizing road data speed limits along a road, lets say from km 0 to
0.76 there is a limit of 50 km/h, from 0.76 to 1.23 there is 80 km/h
limit, etc.

The idea is to symbolize these road segments without having to actually
split the data into bits. And hopefully without having to generate
derived tables that have no link to the original data.

Is QGIS able to do this, perhaps with a plugin?

Thanks for any hints,

Andreas






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