Best practice running Urock with vegetation

[biglimp]

I thought it would be good to have this discussion here so that others can follow.

@j3r3m1 , me and @nilswallenberg are about to start a city-wide (Malmö) run using URock. We have derived building and vegetation with URockPrepare. Running with only buildings is very fast but adding vegetation slows down the modell considerably. We assume it is cos the complexity of vegetation vectors (see below). What would be your suggestion on how to speed things up, i.e. how to simplify the vegetation ploygons without loosing loo much detatil in the output. We are only interest in near-surface wind speed (1.5 magl).

Fredrik and Nils

[j3r3m1]

Well this is indeed crazy long creating the vegetation Röckle zones while it should not. I think that the main reason of this long time was a "bug" (input vegetation geometries were multipolygons and not exploded thus making spatial indexes useless).
With the new version:
With vegetation: 160 s
Without: 50 s

Still not incredible though. Maybe we could merge geometries having nearly the same height (using the vertical resolution as reason to merge two geometries). In general I would say that there is a need to work on the vegetation since most of trees in cities are isolated and some recent works have shown that the URock current scheme for vegetation is not suitable for such trees (cf. our paper describing the URock model).

[biglimp]

When you say new version, is this included in the latest commit? For us is takes (with the data shown above), 32 second only buildings and 879 seconds buildings and vegetation.

How about resampling the vegetation raster to 4 meter and than create input data? I guess we would have less vector polygons to consider...

[j3r3m1]

New version is 2.1.2, pushed 1 hour ago. It should take about a minute and a hald on your computer

Resampling the vegetation to 4 meters can also makes the job indeed, there will not be much differences (maybe none) in the results but it may lead to shorter calculations.

Have a try of the new version and your proposal and report.