[Qgis-user] Metis and creating pyramids

[Maciej Sieczka]

Micha Silver pisze:
> Maciej Sieczka wrote:

>> Regarding rendering perfomance - try to create a TIFF without tiles
>>  (gdal_translate -co "TILED=NO" -co "BLOCKYSIZE=1").

> Many thanks! Your suggestion certainly helped. It seems that giving
> the explicit "TILED=NO" option creates a stripped tiff that loads
> *much* faster. And zooming was very good also.  (BTW I didn't use
> BLOCKYSIZE=1 as that gave an error ).

It shouldn't. It's a valid TIFF creation option [1]. What error exactly?

> In the gdal_translate docs it says that the default (with no TILED= 
> option) is stripped tiff, but that doesn't seem to be the case?

Stripped TIFF is a default gdal_translate output for me. What GDAL
version (I'm using GDAL 1.5.2 + SVN r15027)?

> When I created tiffs with no TILED option they loaded quite slowly.
> Then I added the TILED=YES, and still the images loaded and zoomed
> slowly. TILED=NO gave a dramatic improvement.

>> Anybody knows why QGIS renders tiled rasters without pyramids so
>> slow?

Hey, Developers! Any ideas?

>>> But when I try to create pyramids, it seems to be working for a 
>>> while, then the process ends. But there is no change to the file,
>>> and if I reopen the properties window to the Pyramids tab, all
>>> pixel levels are still marked in red. The tiff's are in my
>>> homedir so, yes, I have write access.

>> For me building pyramids in QGIS works OK.

> I see that with stripped, non-tiled tiff's, I can create pyramids in
> QGIS with no problem. Previously, when I used TILED=YES in 
> gdal_translate, the Create Pyramids didn't do anything. I suppose you
>  wouldn't want or need both tiled tiff and pyramids so maybe it's a 
> feature that zoom levels are not duplicated?

Tiles and overviews (pyramids) are two distinct things and not mutually
exclusive. Applying overviews to a tiled TIFF works for me in QGIS (as
well as for stripped TIFF) and improves it's render times greatly.

Maciek

[1]http://www.gdal.org/frmt_gtiff.html

-- 
Maciej Sieczka
www.sieczka.org