[Qgis-user] Retrieve value from another layer related to its localisation

[Enrico Ferreguti]

You can use refFunctions (http://plugins.qgis.org/plugins/refFunctions/)
plugin that extends Field Calculator with a new Reference group.
Within this group you will find a geomnearest and a geomdistance function
that can help you.

copy and paste from helper screen:

geomnearest function


Retrieve target field value from the nearest target feature in target layer

Syntax

geomnearest(targetLayer,targetField)

Arguments

targetLayer → the name of a currently loaded layer, for example 'myLayer'.
targetField → a field in target layer we want as result when source feature
is within target feature, for example 'myField'.
If targetField is equal to '$geometry' The WKT geometry of targetFeature
willbe retrieved. If otherwise is equal to '$distance' the calculated
distance between source and target features will be returned
Number of feature tested is limited to 100000 to avoid time wasting loops

Example

geomnearest('targetLayer','TargetField')
geomnearest('targetLayer','$geometry')
geomnearest('targetLayer','$distance')


2015-01-15 11:19 GMT+01:00 Junior Delaz <delazj at gmail.com>:

> Hi all,
>
> I have two shapefiles : a line one (called "section") and a point one
> (called "station") shapefiles.
> The line shapefiles has fields like ID_section, ID_first, ID_last
> The point file has an ID_station.
> All these define a kind of network where a section begins on a station and
> ends up at another station.
> What I need to do is to fill :
> - section ID_first field with the ID_station of the station that is the
> closest to the beginning of the section
> - and section ID_last field with the ID_station of the closest station to
> the end of the line.
>
> I can obtain this result while combining many analysis tools and plugins
> (QChainage, Spatial_Join...). I know how I can do it. There might be a way
> with processing tools and if somebody has an idea, I'll be glad to know it
> however.
>
> But what I'm really wondering is if it isn't directly possible to fill
> these fields in the Field calculator using all the nice functions we have.
> Indeed, QGIS 2.6 and RefFunctions plugin give relational fonctions to
> retrieve values on a specific layer according to its fields, features
> values or localisation.
> I tried many combinations with db_query, geomnearest, geomRedef, xat/yat,
> buffer, geometry, within , attribute (not all at the same time :) ).... I'm
> pretty sure it's possible but I can't find. And I don't want to lose all my
> hair...
>
> Does anybody know how I can retrieve in a line shapefile's field the value
> of the point feature that is the closest to the first vertex of this line,
> within the field calculator?
>
> Thanks ...
>
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