[Qgis-user] Display of selected polygon only

[pcreso at pcreso.com]

Hi Agustin,

I believe this depends on how you make the selection. If you open the layer, then use the QGIS select tool to box a region of the map to select the features from the layer, then all the features are displayed using the selected symbology, with the selected features highlighted. If you choose a symbology with no pen or fill, then your layer will effectively be invisible.

There is an alternative selection capability. I recommend storing your data in a Postgis database to get the most benefit from this. When you open a layer, you can use the selection by attribute capability to control which features are filtered out of the underlying dataset to be displayed by QGIS. Thus your entire layer being rendered by QGIS is only a subset of the entire dataset, and your use of the selection tool on this will only highlight the selected features from your subset.

Effectively it is a two stage selection process, allowing to to select which features will comprise your layer, then further select/identify features from this subset.

You might ( if you haven't already ) look at using the action capability
to create an action that allows you to display the image by clicking on it in QGIS. I've used this very effectively for working with seabed imagery in QGIS. 

I'm also working on an application using Postgis & Imagej to allow users to identify & quantify the content of seabed imagery. We are only using a point location for each image, rather than trying to identify the actual area of seabed represented, but this may be of interest to you. This works well with QGIS, and will also be an Open Source application.

HTH,

   Brent Wood




--- On Fri, 12/19/08, Agustin Lobo <aloboaleu at gmail.com> wrote:

> From: Agustin Lobo <aloboaleu at gmail.com>
> Subject: [Qgis-user] Display of selected polygon only
> To: "qgis-user" <qgis-user at lists.osgeo.org>
> Date: Friday, December 19, 2008, 2:54 AM
> Hi!
> 
> I've made a set of polygons with R
> (the bopundaries of images that
> have been acquired with a small UAV)
> and then saved as shp.
> As the set is kind of crowed, when I display in Qgis, I
> would like
> to display only the polygon(s) that
> I have selected in the table, not even
> the boundaries of the rest of polygons.
> Is this possible? By now, if I select
> "no pen" and "no brush", I get nothing
> highlighted.
> 
> Thanks
> 
> -- Dr. Agustin Lobo
> Institut de Ciencies de la Terra "Jaume Almera"
> (CSIC)
> LLuis Sole Sabaris s/n
> 08028 Barcelona
> Spain
> Tel. 34 934095410
> Fax. 34 934110012
> email: Agustin.Lobo at ija.csic.es
> http://www.ija.csic.es/gt/obster
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