[Qgis-user] Slow to open huge rasters

[Nicolas Cadieux]

Hi, 
I have been opening rasters that are much bigger than that lately with no trouble at all. It does take some time but not hours. I have bigger file (80-300GB) but with one band only. I do use a SSD to help out but works with a usb3 drive also. 
The obvious is to check for to see if there is a problem with the hardware (memory, CPU, drive) and to make sure you are not opening the file from a file server (a virtual drive) but from a local hard drive (not a USB key) or a failing HD. 
Try zooming on the zone using a small polygons as a reference, before opening the raster.  Try disabling the "screen render" before opening the raster (right lower corner or Option\Rendering\Rendering behavior. 
An other potential problem is the way the tiff was created.  If, for example the file was created with gdal-Grid (interpolation), then by default, the file was created with an origin from the bottom-left and not upper-left. 
Try resaving the file in QGIS.  Try using the QGIS usual method of saving rasters and also try using gdal-warp with no parameters (raster/projections/warp) (that with change the file origin) then reopen the file.  
Nicolas Cadieux M.Sc. 
Les Entreprises Archéotec inc.  
8548, rue Saint-Denis Montréal H2P 2H2 
Téléphone: 514.381.5112  Fax: 514.381.4995 
www.archeotec.ca 
On Jul 30, 2015 7:49 AM, "Radim Blazek-2 [via OSGeo.org]	" <ml-node+s1560n5217747h18 at n6.nabble.com> wrote: 

	On Thu, Jul 30, 2015 at 11:36 AM, Andrea Peri < [hidden email] > wrote:
> Hi Radim,
> thx for hint.
>
> I try to set the contrast enhancement to NO STRETCH
> and
> Limits to minimum / maximum ,
> Apparently seem to have no result. The qgis is locked in opening of
> raster, but of course I should wait for some hours to see if some
> improvements is occursed.
You can try to uncheck Options > Canvas & Legend > Layer Legend >
Create raster icons
but I don't think that it could help if zoom/pan is fast, so it seems
that there are overviews (pyramids). In fact, even with cumulative cut
it should not be slow if there are overviews because default cut
calculation is using estimated histogram (250000 pixels).
The file is on local hard disk?
Do you see what is happening from debug output?
If you save a project with the raster, the next load of the project is fast?
Radim
> A.
>
>
> 2015-07-30 9:52 GMT+02:00 Radim Blazek < [hidden email] >:
>> On Thu, Jul 30, 2015 at 9:19 AM, Andrea Peri < [hidden email] > wrote:
>>> Hi,
>>>
>>> I have a GeoTiff raster of 24Gbyte, floating point (Float64) with 11
>>> bands and fomat geotiff.
>>>
>>> When try to open it with qgis 2.8.1 I see it take a really uge time to
>>> open it (about 10 hours).
>>> Initially I guess that was a time due to the huge dimension, but after
>>> the qgis show it.
>>> I notice that it is reallyquickly to zoom and pan.
>>> I don't understand why this difference between the open time and zoom/pan time.
>>>
>>> My first suspect was that qgis want to calculate the statistics in first open.
>>> But after a check with gdalinfo I see the statistics are available
>>> also in original tiff.
>>
>> QGIS defaults are stretch to 2/98% cut, try to set in
>> Options > Rendering > Rasters
>> Contrast enhancement: No stretch  or  Limits: Minimum / maximum
>>
>> Radim
>>
>>
>>> So I dont know really why it take so more time to open it.
>>>
>>> I hope to find some setting to reduce the pen time for this kind of images.
>>>
>>> Thx,
>>>
>>> A.
>>>
>>> --
>>> -----------------
>>> Andrea Peri
>>> . . . . . . . . .
>>> qwerty àèìòù
>>> -----------------
>>> _______________________________________________
>>> Qgis-user mailing list
>>> [hidden email] 
>>> http://lists.osgeo.org/mailman/listinfo/qgis-user >
>
>
> --
> -----------------
> Andrea Peri
> . . . . . . . . .
> qwerty àèìòù
> -----------------
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