[Qgis-developer] Re: Raster providers

Radim Blazek radim.blazek at gmail.com
Sun Jan 16 05:50:08 EST 2011

On Thu, Jan 13, 2011 at 7:06 PM, John C. Tull <jctull at gmail.com> wrote:
> You might want to sync the branch to current trunk, although that could create new problems I suppose.

You are right, I should merge trunk more frequently.

> Not surprisingly, the raster transforms can be very costly with large datasets. A hillside of mine that is 26828 × 28695 with 30m resolution takes several minutes to load in full view. When zoomed in considerably, performance is quite acceptable. (This particular file does not have pyramids built. It is noteworthy that the option to build pyramids is no longer available in the raster provider branch. A dialog saying the file type is not supported for pyramid building is shown. In trunk, the pyramid build option works for the same file.)

Pyramids are not yet enabled, at moment I pay attention to correct
basic rendering of all data types in all providers.

> Comparing the load time of this raster when the project CRS is the same as the raster (i.e., no transform should be occurring), the load time still requires several minutes. This is true whether or not I have enabled on the fly reprojection in the project options. In contrast, the same file takes several seconds to load in trunk. Perhaps there needs to be a CRS check on rasters to bypass whatever is happening to consume so many cpu cycles when transforms are unnecessary?

I cannot say if gdal warp is always slow or it could be speed up by
changing init params, I see however that the approximate reprojection
is necessary, so that will be the next step.


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