On 05/04/2011 12:30 AM, scizmeli wrote: > I am reflecting on a data structure that will allow us to perform all kinds > of spectral operations we normally do in remote sensing. Due to lack of an > appropriate data structure supporting spatially based spectral data, right > now we have to keep our data in non-georeferenced N-dimensional arrays. As > for extending spacetime, for now, I can think of an ability to: > > * store in the same spacetime object both the spectral and the non-spectral > products (a spectral radiance image cube+computed image layers);
You can do that already. > * easily subset ranges of wavelengths (hopefully both by wavelength and band > indexes) and be able to easily perform all kinds of space-time operations on > the subsets; you can by number and name, not by wavelength. An issue to consider is that wavelengths for bands are typically intervals, so selecting a range of values, say 500-600 nm, is ambiguous about whether to include a band with range 490-510 yes or no. It would not be that hard to implement; xts lets you select by time range, e.g. "2006" will select all observations in that year. > * select pixels and extract full (or partial) spectra If you mean pixels in space-time, you can, sort of, do that; some manipulation may be needed for the result to be understood as a spectrum, and plotted nicely. > * easily plot different spectral images in lattice panels (with stplot?) for > a given time This would not be too hard. > * some channels are usually too noisy so we would need ability to flag some > unwanted channels at some pixels > * store spectral data for point and trajectory measurements That is foreseen in the next few months. > * incrementally import high volumes of data without having to load at once > all the data in memory. Size of spectral image times series can be very > large. On-disk storage can be sought with the use of netcdf technology for > extremely large databases. This was identified as one of the priorities on the workshop we organized last March (www.opengeostatistics.org). I'm not sure how fast such a feature will arrive. > > and ability to easily implements methods like : > > * band-ratio (or all kinds of other arithmetic) operations to compute new > image layers. > * computation of things like spectral derivatives, spectral unmixing as well > as classification algorithms that use spatial/spectral information together > etc. > * overlay ground truth data (ship trajectory/ground truth points/polygons) > onto image time series to match image pixels with ground truth data based on > spatial coordinates and time information (ship trajectories will coincide > with satellite images only at some given days) > * easily plot different spectra (graph of measurement wrt wavelenth) for a > given pixel in panels (or in the same graph) for different times (with > stplot?) > * spectrally interpolate images with a high spectral resolution to estimate > non-existing channels > > There will certainly be dimensions other than "spectral" that people from > other disciplines will want to add in a spacetime object. So, to my mind, it > all boils down to the ability of adding custom dimensions into a spacetime > object (with numeric/string attributes addressable as in > st[pixel,time,wavelength,otherdimension] > > If the upcoming versions of the spacetime package can be designed in such a > way, we could start implementing methods on spacetime objects for our tasks > in hand and the package would very fast become popular. > > Are any these ideas feasible? I think so. What is lacking is a large amount of enthousiasm, use cases, and programming efforts! > Servet > > PS: I am definitely ready to help if you think this is a good direction to > go. I never created new object/methods myself but I am committed to learn > pretty fast if some initial directions are given. O.K.; then I'd recommmend the book "S programming", or something similar, to get up to speed, or one of John Chambers' books on R programming. Best wihses, > > -- > View this message in context: > http://r-sig-geo.2731867.n2.nabble.com/spacetime-adding-a-fourth-spectral-dimension-tp6306599p6329040.html > Sent from the R-sig-geo mailing list archive at Nabble.com. > > _______________________________________________ > R-sig-Geo mailing list > R-sig-Geo@r-project.org > https://stat.ethz.ch/mailman/listinfo/r-sig-geo -- 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.pebe...@wwu.de _______________________________________________ R-sig-Geo mailing list R-sig-Geo@r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-geo