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

[Nyall Dawson]

On Thu, 24 Jan 2019 at 23:05, Andreas Neumann <a.neumann at carto.net> wrote:

> My data is originally coming from an ESRI ascii grid. It had been many hundred tiles of ascii grids which I merged into a single big GEOTIFF file. The original data had up to 3 digits after the decimal point for the terrain height (mm accuracy) per cell. After import to the Geotiff the data has now many more (useless) digits after the comma, because the number of the digits in the geotiff is now defined by the float32 data type I chose. When I export that data back to ESRI ascii grid I get 15! digits after the decimal point. I would like to round it back to 2 digits after the decimal point (cm accuracy).

I might be missing something, but it sounds like this change in
precision has happened at the conversion to geotiff stage, not the
"clip raster by extent" stage?

Does converting the grids to a single vrt, and then using GDAL
translate to convert the combined vrt directly to an ascii grid help?

Nyall


>
> In addition, the header in the resulting asciigrid has now many useless digits. It looks like this:
>
> ncols 233
> nrows 189
> xllcorner 2681471.893245012965
> yllcorner 1224297.020738559077
> dx 0.999927877238
> dy 1.000035130719
> NODATA_value 0
>
> Note that the resolution of the data is 1m. But in the export it comes out as dx 0.999927877238 - dy 1.000035130719



>
> I wonder if I could force the resolution back to 1.0 (the original resolution).
>
> So it is an issue of rounding/accuracy.
>
> Thanks again,
>
> Andreas
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