[Qgis-user] Slow to open huge rasters

[Radim Blazek]

On Thu, Jul 30, 2015 at 11:36 AM, Andrea Peri <aperi2007 at gmail.com> 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 <radim.blazek at gmail.com>:
>> On Thu, Jul 30, 2015 at 9:19 AM, Andrea Peri <aperi2007 at gmail.com> 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
>>> -----------------
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>
>
>
> --
> -----------------
> Andrea Peri
> . . . . . . . . .
> qwerty àèìòù
> -----------------