[gdal-dev] Multidimensional raster support in GDAL

[Ari Jolma]

Even Rouault kirjoitti 25.10.2017 klo 22:22:

> On mercredi 25 octobre 2017 14:42:54 CEST Ari Jolma wrote:
>
> > I'd like to first know / decide what would we mean by a
>
> > "multidimensional raster"?
>
> The current rasters handled by GDAL are already multidimensional
>

I was aiming at the 'multidimensional raster' to a case where the 
location (raster cell) data is multidimensional. You get 
multidimensional data whenever you have an axis along which you can do 
measurements (time, depth, electromagnetic spectrum, simulation number, 
etc). I'd take the location as the basis that probably shouldn't need 
extending for GDAL. Or do we want to support taking X,Y,T data from a 
format that supports it and slice it to X,T for another format? Maybe 
that makes sense for some visualization and analysis purposes, but is 
that what GDAL should support at some point? Are there compelling use cases?

Would it be possible to keep X,Y as it is and add support for 
multidimensional data as an extension?

Ari


> , with the number of dimensions being fixed to 2, and being 2 
> horizontal dimensions (X/Y, lon/lat). The idea here would be to at 
> least address the 3D (X,Y,Z / X,Y,T) and 4D case (X,Y,Z,T), and when 
> you need to do that, arbitrary number of dimensions is at hand.
>
> The dimensions/ones here are mostly spatio-temporal ones, along which 
> you can measure a physical phenomenon (a temperature field measures at 
> different position, elevation, time)
>
> >
>
> > What we now have as a raster is a dataset with one or more bands. The
>
> > bands represent the data dimension and thus there is one of those
>
> > (2D+1).
>
> Bands do not represent a dimension. In OGC SIS
>
> ( http://docs.opengeospatial.org/is/09-146r6/09-146r6.html ) or WCS, 
> bands are called fields of a rangeType.
>
> Bands are different from the above mentionned dimensions in which they 
> do not really consider an axis along which you have some consistency. 
> Along the X/Y axis, you can mark ticks every n meters. Along the "band 
> axis", you will have a temperature field in Kelvin, a wind direction 
> in degrees, etc.
>
> > Would we like to have more data dimensions? What Even sketches
>
> > below is ND, but would we really want to have 2D + ND?
>
> My scetch of ND intended to capture the current 2D case, as a 
> particular case.
>
> >
>
> > Also now there is no unit for the data dimension and the value is
>
> > strictly increasing positive integer,
>
> > would we like to have an explicit
>
> > unit
>
> Was the GDALDataset::char* apszAxisUnit[nAxisCount] or 
> GDALGridAxis::pszUnit in my scetch
>
> > and arbitrary value (double, date, time, ...)?
>
> In my scetch, I had indeed some hesitation about the appropriate type 
> for adfAxisCoordinates array. I think that for the cases mentionned 
> above (4D spatio-temporal) we can always represent the coordinates 
> along each axis as a double value. The case where that's the less 
> obvious is for date/time, but using some reference like the Unix Epoch.
>
> Even
>
> -- 
>
> Spatialys - Geospatial professional services
>
> http://www.spatialys.com
>

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