[QGIS-Developer] 2 questions on saving rasters in 3.4

Andreas Neumann a.neumann at carto.net
Fri Jan 25 01:07:24 PST 2019

Hi Luke,

Excellent. I should have consulted the GDAL reference myself ;-) many 
thanks. This was exactly what I was looking for!

I can define the DECIMAL_PRECISION parameter as an advanced option when 
creating the raster. This works very well.

The only issue I see here is "user friendly-ness". While this works very 
well for an experienced user, we can't expect the average user or even 
novices to find out these parameters by themselves  by consulting the 
GDAL documentation.



Am 25.01.19 um 03:09 schrieb Luke Pinner:
> For ASCII grids, the gdal doc[1] notes:
> When writing floating-point values, the driver uses the "%.20g" format 
> pattern as a default. You can consult a reference manual 
> <http://en.wikipedia.org/wiki/Printf> for printf to have an idea of 
> the exact behaviour of this ;-). You can alternatively specify the 
> number of decimal places with the DECIMAL_PRECISION creation option. 
> For example, DECIMAL_PRECISION=3 will output numbers with 3 decimal 
> places(using %lf format). Starting with GDAL 1.11, another option is 
> SIGNIFICANT_DIGITS=3, which will output 3 significant digits (using %g 
> format).
> I don't know if you can specify gdal creation options for AAIGRID 
> output in QGIS 3 though.
> 1 https://www.gdal.org/frmt_various.html
> On Thu., 24 Jan. 2019, 18:59 Andreas Neumann <a.neumann at carto.net 
> <mailto:a.neumann at carto.net> wrote:
>     Hi,
>     I have two questions about saving rasters in QGIS 3.4:
>     1.
>     If I use "Right-klick layer" --> "Export" --> "Save AS" then I
>     can't choose the ESRI ASCII Grid format described in "Settings"
>     --> "Options" --> "GDAL" as "AAIGrid".
>     Any idea why this format is not available for exporting rasters?
>     2.
>     As an alternative I can use the "Raster" --> "Extraction" -->
>     "Clip raster by extent". This works fine, but I can't set the
>     number of decimal places after the comma.
>     E.g. if I export a terrain model I would like to use 2-3 places
>     after the decimal, not the full 8 digits, which is a false accuracy.
>     Any way I can set the accuracy for the export?
>     Thanks,
>     Andreas
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