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 <[email protected]> wrote:

> From: Agustin Lobo <[email protected]>
> Subject: [Qgis-user] Display of selected polygon only
> To: "qgis-user" <[email protected]>
> 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: [email protected]
> http://www.ija.csic.es/gt/obster
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