[Qgis-user] Raster - values and histogram

[Lene Fischer]

Hi Nicolas,
I have now been reading into the vrt file.
All Nodata are the same -9999

It seems as if the vrt file takes the min max value from the first rasterfile. I have compared data in the browser.
If I go to style>properties and load ‘min-max’ actual values. These values are written into the vrt-file.
So when I close and reopen the vrt file it is back to start again.

It seems to be a bug.
Could you do me a favor and try this out before I´ll file a ticket.

Regards
Lene Fischer

Fra: Qgis-user [mailto:qgis-user-bounces at lists.osgeo.org] På vegne af Nicolas Cadieux
Sendt: 17. april 2016 14:48
Til: qgis-user at lists.osgeo.org
Emne: Re: [Qgis-user] Raster - values and histogram


Hi,

I am not sure if there is a bug but since you have a virtual raster, I would look to see if they all have the same no data values.  Try loading only one raster or try saving the virtual raster as a tif  and setting the no data value.  Do you have the same problem?

If Qgis does not recognize the no data value, it may be thrown out by trying to stretch the image from -32768 to whatever you have.  In that case, your raster will not be "viewed correctly" as it is trying to display more than 256 shades which is the max a screen can handle. In that case you would see only black and white.

Hope this help!
Nicolas
On Apr 17, 2016 8:22 AM, "Lene Fischer [via OSGeo.org]" <[hidden email]</user/SendEmail.jtp?type=node&node=5261625&i=0>> wrote:

Hi,

I´m rehearsing my lectures for tomorrow – and using 2.14.1 on windows.



When I create a virtual raster the values are not viewed correct. Then I click Stretch Histogram to full data. Nothing happens.

I have to go to properties and load to ‘min-max’ actual values before anything happens.



If I use Properties >Histogram and try to Reset and then ReCompute histogram – nothing happens…



What do I do wrong?



A bit distressed – Giving lectures in raster QGIS tomorrow …

Regard

Lene Fischer

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