Glynn Clements wrote: > > 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. >
You are right. Do you still vote against the patch in general (along with better documentation)? Markus -- View this message in context: http://www.nabble.com/r.series-threshold-patch-tf4280608.html#a12238104 Sent from the Grass - Dev mailing list archive at Nabble.com. _______________________________________________ grass-dev mailing list grass-dev@grass.itc.it http://grass.itc.it/mailman/listinfo/grass-dev
