[GRASS-user] Best workflow

[Paul Meems]

Thanks Stefan,

I didn't thought of gdalbuildvrt. I'll try that option.
The polygons do not overlap and I'm not sure about the height data. Perhaps
they overlap a bit.

What I need to do in GRASS is:

   - call r.slope.aspect to calculate the slope and aspect. I had planned
   doing this for every polygon but when I'm going to use gdalbuildvrt I can
   do it for the whole dataset in one time.
   Is that a good choice? The height data spans The Netherlands and has
   0.5m resolution. Can GRASS handle such a big dataset?
   - Next command is r.mapcalc. This can be done on a subset or on the
   whole dataset at once.
   - Then I need to call r.to.vect. I think it is best to do this for a
   subset because I only need the part within the polygon. I think I can set
   the region to the polygon and then call r.to.vect to speed this up, right?
   - Then I need to clip with the border and export this vector dataset to
   PostGIS.

With the above workflow I don't think I need to convert the polygons to
raster first, right?
I'm reading https://grasswiki.osgeo.org/wiki/PostGIS and I'm using GRASS v7
so if I understand it correctly I can link a PostGIS table using v.external
Can I then loop through each feature and perform the above workflow and
also update a field in PostGIS called something like 'processed' and set it
to True?
And am I right I can do this all using Python? I'm running Ubuntu server so
no GUI available.

Thanks

Paul


2016-06-24 10:17 GMT+02:00 Blumentrath, Stefan <Stefan.Blumentrath at nina.no>:

> > *From:* grass-user [mailto:grass-user-bounces at lists.osgeo.org] *On
> Behalf Of *Paul Meems
>
>
>
> Depends on several things, e.g
>
> -        do polygons overlap or not,
>
> -        do “height maps” overlap or not?
>
> -        What are the “several commands” you need to be performed
>
>
>
> On the basis of the information you provided I would have a look at
>
>
>
> -        gdalbuildvrt for merging your “height map” tiles
>
> -        import PostGIS polygon table to GRASS
>
> -        convert to raster using v.to.rast and assign ID to each raster
> representation of your polygons
>
> -        calculate statistics using either
>
> o   r.stats
>
> o   r.univar
>
> to create CSV files, which can be read back to PostGIS (COPY command) and
> then joined to your original map using ID field
>
>
>
> I would not consider WCS / GeoServer, that gives you only overhead and
> extra work...
>
>
>
> Cheers
>
> Stefan
>
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