[gdal-dev] ASCII Gridded XYZ and "Hectare Raster" data (STATPOP and STATENT)

[Stefan Keller]

Hi Even

Thx very much!
I'll try that way and will report.

:Stefan

Am So., 21. Apr. 2019 um 11:31 Uhr schrieb Even Rouault
<even.rouault at spatialys.com>:
>
> Stefan,
>
> >
> > The Swiss Statistical Office curates well-known datasets informally
> > called "Hectare Raster" (STATPOP and STATENT) which obviously are
> > ASCII Gridded XYZ, like this:
> >
> > "RELI" "X" "Y" "C1" "C2" "C3"
> > 66192542 661900 254200 1 2 3 ...
> > 66192543 661900 254300 1 2 3 ...
> > 66192599 661900 259900 1 2 3 ...
> > 66192600 661900 260000 1 2 3 ...
> > ...
> >
> > This obviously is a regular gridded X and Y, sorted by X,Y but
> > obviously also has gaps and more than one  "Z" (C1, C2, C3). Typically
> > this is converted to a raster format like GeoTIFF and analysed through
> > map algebra.
> >
> > Question 1: The GDAL docs (https://www.gdal.org/frmt_xyz.html ) says
> > "...no missing value is supported.". In fact, I think it supports them
> > by omitting lines by setting missing "lines" to NODATA.
> > => Correct?
>
> The driver is quite picky. I don't think it will support missing values in the
> middle of a line of same Y value. It supports missing values at the beginning
> or end of a line of same Y value. And points must be sorted by increasing or
> decreasing Y, and increasing X value for a line of same Y value.
>
> >
> > Question 2: I think, there is a way (which could be mentioned in the
> > docs above), to determine the "Z" value to be converted by gdal_grid
> > explained in "Reading comma separated values"
> > (https://www.gdal.org/gdal_grid.html#gdal_grid_csv ).
> > So XYZ in fact is XYZx meaning that potentially there can be many "Z"
> > in the input file, but only one can be included.
> > => What do you think?
>
> The best way might probably to read the file with the CSV driver indeed. With
> CSV:the_filename if the_filename has not a .csv extension
> Convert it to something with a spatial index like a shapefile or GPKG if the
> file is big
> And then use gdal_grid to create a raster from it.
>
> >
> > Question 3 (the fundamental one): Although XYZ format requires to
> > contain regular gridded coordinates, it's technically handled the same
> > as irregular coordinates (without interpolation) - at least regarding
> > the main task to convert an sparse array of values to a raster format.
> > => Correct?
>
> The XYZ driver requires constant spacing.
>
> Even
>
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