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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Hi Paul,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Sure, GRASS and Python is a powerful combination. See:
<a href="https://grasswiki.osgeo.org/wiki/GRASS_and_Python">https://grasswiki.osgeo.org/wiki/GRASS_and_Python</a> and
<a href="https://grasswiki.osgeo.org/wiki/GRASS_Python_Scripting_Library">https://grasswiki.osgeo.org/wiki/GRASS_Python_Scripting_Library</a><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">But there are others on this list that are much more competent than I am on this topic.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">GRASS 7 is definitely the right choice for heavy datasets.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">However, is it really necessary to use 0.5m resolution for you purpose?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">If yes, have a look at this:
<a href="https://grass.osgeo.org/grass70/manuals/libpython/pygrass.modules.grid.html">
https://grass.osgeo.org/grass70/manuals/libpython/pygrass.modules.grid.html</a><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Or this:
<a href="https://grasswiki.osgeo.org/wiki/Parallel_GRASS_jobs">https://grasswiki.osgeo.org/wiki/Parallel_GRASS_jobs</a><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Not sure about the performance for r.external and VRT mosaics... So, you might be better off running parallel jobs for
each tile (e.g. each tile in it`s own mapset)... And that you finally collect the results for all tiles...<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">If you want to assign raster values to polygons you will have to rasterize them (which is v.rast.stats https://grass.osgeo.org/grass70/manuals/v.rast.stats.html
does).<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Keep in mind that v.external does not build a proper topology. That might be unsafe...<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Cheers<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Stefan<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> Paul Meems [mailto:bontepaarden@gmail.com]
<br>
<b>Sent:</b> 24. juni 2016 11:35<br>
<b>To:</b> GRASS user list <grass-user@lists.osgeo.org><br>
<b>Cc:</b> Blumentrath, Stefan <Stefan.Blumentrath@nina.no><br>
<b>Subject:</b> Re: [GRASS-user] Best workflow<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Thanks Stefan,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I didn't thought of gdalbuildvrt. I'll try that option.<o:p></o:p></p>
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<p class="MsoNormal">The polygons do not overlap and I'm not sure about the height data. Perhaps they overlap a bit.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">What I need to do in GRASS is:<o:p></o:p></p>
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<li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
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.<br>
Is that a good choice? The height data spans The Netherlands and has 0.5m resolution. Can GRASS handle such a big dataset?<o:p></o:p></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
Next command is r.mapcalc. This can be done on a subset or on the whole dataset at once.<o:p></o:p></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
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?<o:p></o:p></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
Then I need to clip with the border and export this vector dataset to PostGIS.<o:p></o:p></li></ul>
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<p class="MsoNormal">With the above workflow I don't think I need to convert the polygons to raster first, right?<o:p></o:p></p>
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<p class="MsoNormal">I'm reading <a href="https://grasswiki.osgeo.org/wiki/PostGIS">https://grasswiki.osgeo.org/wiki/PostGIS</a> and I'm using GRASS v7 so if I understand it correctly I can link a PostGIS table using <span style="font-size:10.5pt;font-family:"Courier New";color:black;background:#F9F9F9">v.external</span><o:p></o:p></p>
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<p class="MsoNormal">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?<o:p></o:p></p>
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<p class="MsoNormal">And am I right I can do this all using Python? I'm running Ubuntu server so no GUI available.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Thanks<o:p></o:p></p>
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<p class="MsoNormal"><br>
Paul<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">2016-06-24 10:17 GMT+02:00 Blumentrath, Stefan <<a href="mailto:Stefan.Blumentrath@nina.no" target="_blank">Stefan.Blumentrath@nina.no</a>>:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">>
<b>From:</b> grass-user [mailto:<a href="mailto:grass-user-bounces@lists.osgeo.org" target="_blank">grass-user-bounces@lists.osgeo.org</a>]
<b>On Behalf Of </b>Paul Meems</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Depends on several things, e.g
</span><o:p></o:p></p>
<p><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">-</span><span lang="EN-US" style="font-size:7.0pt;color:#1F497D">
</span><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">do polygons overlap or not,
</span><o:p></o:p></p>
<p><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">-</span><span lang="EN-US" style="font-size:7.0pt;color:#1F497D">
</span><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">do “height maps” overlap or not?</span><o:p></o:p></p>
<p><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">-</span><span lang="EN-US" style="font-size:7.0pt;color:#1F497D">
</span><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">What are the “several commands” you need to be performed</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">On the basis of the information you provided I would have a look at
</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"> </span><o:p></o:p></p>
<p><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">-</span><span lang="EN-US" style="font-size:7.0pt;color:#1F497D">
</span><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">gdalbuildvrt for merging your “height map” tiles</span><o:p></o:p></p>
<p><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">-</span><span lang="EN-US" style="font-size:7.0pt;color:#1F497D">
</span><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">import PostGIS polygon table to GRASS</span><o:p></o:p></p>
<p><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">-</span><span lang="EN-US" style="font-size:7.0pt;color:#1F497D">
</span><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">convert to raster using v.to.rast and assign ID to each raster representation of your polygons</span><o:p></o:p></p>
<p><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">-</span><span lang="EN-US" style="font-size:7.0pt;color:#1F497D">
</span><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">calculate statistics using either</span><o:p></o:p></p>
<p style="margin-left:72.0pt"><span lang="EN-US" style="font-size:11.0pt;font-family:"Courier New";color:#1F497D">o</span><span lang="EN-US" style="font-size:7.0pt;color:#1F497D">
</span><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">r.stats</span><o:p></o:p></p>
<p style="margin-left:72.0pt"><span lang="EN-US" style="font-size:11.0pt;font-family:"Courier New";color:#1F497D">o</span><span lang="EN-US" style="font-size:7.0pt;color:#1F497D">
</span><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">r.univar</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:35.4pt">
<span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">to create CSV files, which can be read back to PostGIS (COPY command) and then joined to your original map using ID field</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:35.4pt">
<span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">I would not consider WCS / GeoServer, that gives you only overhead and extra work...</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Cheers</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Stefan</span><span style="color:#888888"><o:p></o:p></span></p>
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