[Qgis-user] Linear referencing in QGIS

[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.neumann at 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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-- 
Régis Haubourg

Attention, changement d'adresse mail!
Mon adresse principale devient désormais regis.haubourg at gmail.com
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