[Qgis-user] Linear referencing in QGIS

[Bernhard Ströbl]

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.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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