[Qgis-user] Slow to open huge rasters

Thu Jul 30 06:58:12 PDT 2015

Spinning disks can be significantly slower than an SSD :( However, I've
opened 10GB, 3-band rasters off spinning platter disks in seconds, so :-\
Some calculations on band cutoffs and things can take a while if I ask it
to calculate those.

On Thu, Jul 30, 2015 at 9:50 AM, Nicolas Cadieux <
nicolas.cadieux at archeotec.ca> wrote:

> 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] " <[hidden email]
> <http:///user/SendEmail.jtp?type=node&node=5217781&i=0>> wrote:
>
> On Thu, Jul 30, 2015 at 11:36 AM, Andrea Peri <<a
> href="/user/SendEmail.jtp?type=node&node=5217747&i=0">[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 <<a
> href="/user/SendEmail.jtp?type=node&node=5217747&i=1">[hidden
> email]>:
> >> On Thu, Jul 30, 2015 at 9:19 AM, Andrea Peri <<a
> href="/user/SendEmail.jtp?type=node&node=5217747&i=2">[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
> >>> <a
> href="/user/SendEmail.jtp?type=node&node=5217747&i=3">[hidden
> email]
> >>> http://lists.osgeo.org/mailman/listinfo/qgis-user
> >
> >
> >
> > --
> > -----------------
> > Andrea Peri
> > . . . . . . . . .
> > qwerty àèìòù
> > -----------------
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