[R-sig-Geo] spacetime : adding a fourth (spectral) dimension

[Edzer Pebesma]

On 04/26/2011 07:15 PM, scizmeli wrote:
> I have recently been introduced to the promising package called spacetime
> which helps solve some of the data management problems we regularly
> encounter with time-series of spatial data. I would like to congratulate the
> developers of this wonderful package.

Thanks for the encouragement!
> 
> My question : Is there a way to incorporate in a spacetime object additional
> dimensions? For example, in remote sensing, we regularly deal with time
> series of spectral imagery. I can easily think of a 5-D model output
> (timeseries of a 3-d model of a spectral parameter). In such a case, it
> would also be useful to be able to specify auxiliary data for each band i.e.
> wavelength information and its units (412 nm, 515 nm etc). It would of
> course be better if these auxiliary data can be defined in a custom-manner.
> 
> If this is not possible for now, can it be considered in the near future?
> Spatial data nowadays can easily have more than 3 dimensions and it would be
> very useful seeing this addressed by the spacetime package.
> 

Yes and no. In a spacetime object st,

st[i,j,k]

has index k to refer to the attribute, and this can indicate the band
number (1:n) or name (B412,B515, etc). So yes, there is room in these
objects for multiple bands, but not as generic as array() does --
although that has its limits too.

Also, the wavelength information is "lost", or needs encoding in
attribute names, which is annoying when you need to decode. I can see a
relatively simple option of subclassing one of the available classes to
a class for multispectral data that holds an attribute (or slot) with
the wavelength information (wavelength values, or intervals per
attribute) and allow selection options like

st[,,"412::515"]

to select all bands in this particular range.

Which use cases, or particular demands, did you have in mind to
manipulate objects? What is the typical thing you do with these data
that you'd like to do with R / spacetime?

> Servet
> 
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-- 
Edzer Pebesma
Institute for Geoinformatics (ifgi), University of Münster
Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251
8333081, Fax: +49 251 8339763  http://ifgi.uni-muenster.de
http://www.52north.org/geostatistics      e.pebesma at wwu.de