Hi Graeme,
as I wrote in my last mail you can set a filter for a layer. This does
exacly what you describe. Changing the filter according to a changed
selection in another layer and zooming to the new set sounds like a
plugin, though.
An non-plugin approach would be to create a view on the db that joins
zones and roads spatially (e.g. ST_Intersects). If you load this view
into QGIS you can select the road network layer by attribute zone_id,
then zoom to the selected road segements. Be aware that QGIS needs a
unique key for any layer.
Bernhard
Am 24.02.2017 um 15:34 schrieb SEGGIE Graeme:
Brent / Bernhard,
Thanks both for the detailed responses. It does look like I am
re-inventing a process that can be done as an informed user, I suppose
the example I suggested might be too simple to be worth going to the
lengths I described, but I was thinking of some of the manual processes
I see on editing data and wanted to refine a process to be such that
repetitive steps could be minimised somehow.
I see some stuff from both your responses worth me looking into anyway
even if not pursuing my original approach, which is good.
I have played some more with this, but am struggling to see how I would
do the following, which seems like a logical thing to do with QGIS
acting as a front end to a database. If I have a zone layer and a road
network layer, how do I link the two such that the selection in one
layer impacts the view of the other? For example, if I select a zone, I
would like that selected zone_id, to be passed to PostGIS, to identify
the roads which intersect the selected zone and only display them (or
display them as dominant) as selected in the network layer. Is there a
way of filtering one layer on the selection of another i.e. filter on
where zone_id in (selected zone_id in layer X)
Graeme.
Hi Graeme,
QGIS can do what you describe in your example out of the box.
Workflow:
0) copy layer
1) select polygon in layer
2) use the spatial query plugin
- select source from layer_copy
- Where the feature intersects
- reference features of layer (tick 1 selected polygon)
- apply
3) zoom to selection of layer_copy
If you work with PostGIS you can use the layer's filter to enter any SQL
thus restricting the features to those that fit into the filter rule.
Then zoom to the layer and you are done.
You can load the result of a query against a PostGIS DB as layer into
QGIS, too, by using DB manager.
For automation Processing's graphical modeler might be worth looking at.
Of course you can do most things with a plugin that you e.g. connect to
a layer action. I am always reluctant to write a plugin for workflows
that can be performed using QGIS' standard tools, though.
I know users like to klick on a dedicated button and then something is
run just the way they (think they) need it, however IMHO the smarter
approach is to train the users to do these tasks themselves with the
standard tools.
Bernhard
…
Sort of in the area you are asking about:
See the Action tool
Under Windows this can invoke a batch file to display the result of an
sql for data about the (Postgis) feature clicked on. Even easier under
Linux with a bash script. If one of the fields is an image file, you can
create an action to display the image associates with the feature. A
useful bit of functionality...
But to do exactly what you are asking, I think the Attribute table does
this, so it is a matter of explaining the steps to your users, rather
than writing code...
If you select a set of features in a Postgis (or most type of layer)
layer rendered on the map, QGIS highlights the selected ones as defined
in the project properties. Open the Attribute table for the layer, you
will see the selected features, not only highlighted on the map, but
also in the attribute list. Click the "move selected features to top"
button, and the selected/highlighted features will always be at the top
of the list. The attribute table has buttons at the top to zoom & pan to
selected features...
Cheers,
Brent
------------------------------------------------------------------------
*From:*SEGGIE Graeme <gseg...@systra.com <mailto:gseg...@systra.com>>
*To:* "Qgis-user@lists.osgeo.org <mailto:Qgis-user@lists.osgeo.org>"
<Qgis-user@lists.osgeo.org <mailto:Qgis-user@lists.osgeo.org>>
*Sent:* Friday, February 24, 2017 6:48 AM
*Subject:* [Qgis-user] Simple methodology for user / data / map
interactivity?
I would like to use QGIS as a visual / interactive front to some PostGIS
data and am not sure what the best route to doing so is. Happy to
explore further myself, but wanted to get some input on what needs to be
joined up to get started on building a little process.
Basically, if I wanted to present a map of features and have a button
(like the attribute information one) which a user would click then use
to select features, I want this to run a SQL query which to get related
features for example and highlight them on the map view, possibly pan to
the extent of the newly selected feature set.
Does this sound like a plugin – or would that be taking things too far?
Would the best way for the dynamic layer to be setup, to be a view –
empty except when populated by the query and styled to be dominant over
the full set of features?
As a simple example, say I had a district zone system of polygons and I
wanted a user to be able to click on any polygon, and have all the
neighbouring polygons highlighted, centred and fill the map view as
fully as possible. What would be the best / simplest approach to this?
Graeme
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