Markus Neteler wrote: > >> to easier operate on incomplete time series from MODIS (and > >> others), we would like to suggest attached patch. It > >> adds a threshold to filter out incomplete pixel series > >> before calling the aggregation function which saves us > >> to perform extra runs on counting valid pixels and to > >> post-filter the aggregated results. > > > > While I don't doubt that this is a useful optimisation for your > > particular case, I'm generally opposed to adding such optimisations > > for specific cases. > > > > A more general optimisation would be to extend the method= and output= > > options to accept multiple values, so that you can compute multiple > > aggregates in a single run. You would still need to combine the two > > outputs with e.g. r.mapcalc, but you would only need one run of > > r.series. > > > The optimization you propose is of course far more general than what > we did, and could be extremely valuable. > > Nonetheless, we think that introducing the threshold parameter is not > really a special case hack: all it really does is a straightforward > generalization of the current -n flag, transforming it from a ON/OFF > switch to an integer value. > > The threshold parameter indicates the minimum number of non NULL > inputs required for passing over the inputs to the aggregation > function. > > It varies in the range [1,num_inputs]; thresh=num_inputs is equivalent > to -n (return NULL unless the inputs are all non NULL), while thresh=1 > is the standard behaviour (compute the aggregation if there is at > least 1 non NULL input).
Actually, thresh=0 would give the existing behaviour. If -n isn't used, the values are always passed to the aggregate function. If all of the values are null, most aggregates will return null, but the "count" aggregate will return 0. -- Glynn Clements <[EMAIL PROTECTED]> _______________________________________________ grass-dev mailing list [email protected] http://grass.itc.it/mailman/listinfo/grass-dev
