'Re: [Qgis-user] vector point grid to raster grid -- pixel size does not work SOLVED'

[prev in list] [next in list] [prev in thread] [next in thread] 

List:       qgis-user
Subject:    Re: [Qgis-user] vector point grid to raster grid -- pixel size does not work SOLVED
From:       "Priv.-Doz. Dr. Maria Shinoto" <maria.shinoto () zaw ! uni-heidelberg ! de>
Date:       2020-05-16 10:12:58
Message-ID: 6A9827EB-EE0A-4E32-B6E3-CF46347B54B6 () zaw ! uni-heidelberg ! de
[Download RAW message or body]

Hi, 

I had some intensive learning during the last days, and thanks again for your help. 

After all it turns out that it is something Nicolas wrote, it is a matter of the \
projection. The Japanese software just exported to a projected format, but the \
original data seem to be in lat long. I found a way to get the unprojected data and \
now can create a beautiful hillshade in an unprojected lat long layer. And it even \
looks good in a projected project (EPSG:6670) with on the fly projection. 

For hydrological analyses I need to use the projected data, but the artifacts do not \
matter here. While binge-watching YouTube videos I realized that these artifacts \
occur with the pros as well when they use the projected layers for their analyses. \
Now everything much better and "in place".

Best, 
Maria

> Am 15.05.2020 um 13:21 schrieb Nicolas Cadieux <nicolas.cadieux@archeotec.ca>:
> 
> 
> 
> Nicolas Cadieux
> Ă‡a va bien aller!
> 
> > Le 14 mai 2020 Ă  23:12, Nicolas Cadieux <nicolas.cadieux@archeotec.ca> a Ă©crit \
> > : 
> > ď»żHi,
> > 
> > 
> > See below for comments.
> > 
> > Nicolas Cadieux
> > Ă‡a va bien aller!
> > 
> > > Le 14 mai 2020 Ă  22:21, Priv.-Doz. Dr. Maria Shinoto \
> > > <maria.shinoto@zaw.uni-heidelberg.de> a Ă©crit : 
> > > ď»żHi again, 
> > > 
> > > and sorry for the ongoing discussion.
> > > 
> > > Today I exported a selection of the DEM data to a shapefile, just 9MB for the \
> > > main file, and this makes testing very fast. 
> > > (A) TINs did not work. 
> > 
> > TIn interpolation has memory problems with large data sets.  Same problem since \
> > QGIS 2x at least.  It was cool features but is not made to handle today's data \
> > sets.
> > > 
> > > (B) I tried all steps carefully again, but even the GDAL raster is horrible \
> > > now.  
> > > Here are some screenshots with my explanation and the protocol for \
> > > rasterization and filling nodata.  
> > > It seems that the artifacts are due to no data fields that evolve during \
> > > rasterization as a pattern. These nodata fields may be due to a slight \
> > > inclination of the grid from the export of the data with the Japanese software. \
> > >  
> > > 1) The point grid, one can see the inclination
> > > 
> > <01.jpeg>
> > > 
> > > 
> > > 2) The raster of the same area, one can see the points of the vector point grid \
> > > along the white empty space; this is NODATA. 
> > <02.jpeg>
> > > 
> > > 
> > I would use gdal_grid not rasterize. Use Gdal grid with a larger search circle \
> > will solve this problem.  Use nearest neighborhood with a search radius larger \
> > than the pixel (like 7m).  That will reduce the no data. Click on the help or go \
> > to the gdal website. That will help you add the missing parameters like the -txe \
> > and -tye. (The extent) and the -outsize for the number of pixels.  
> > > I add the protocol
> > <2020-05-15-rasterize-protocol-for-selection.txt>
> > > 
> > > 
> > > 
> > > 3) Using the Fill NODATA from the Raster menu makes a beautiful looking raster, \
> > > there seem to be no flaws. 
> > <03.jpeg>
> > > 
> > > 
> > 
> > That fixes things but adds new data to the raster. This may be unwanted.
> > 
> > > I add the protocol.
> > > 
> > <2020-05-15-fill-nodata-protocol-for-selection.txt>
> > > 
> > > 
> > > 4) This is the same area as in (3), but instead of a pseudocolor ramp shown as \
> > > hillshade. 
> > <04.jpeg>
> > > 
> > > 
> > This is normal if you select a bad z factor (probably not the case here).  You \
> > will have the same thing if you zoom in and have nearest neighbour in the "zoomed \
> > in" under "resampling" in the hillshade symbology window.
> > > 
> > > 5) This is the impression from a larger area.
> > > 
> > <05.jpeg>
> > > 
> > > 
> > > 
> > > 6) This is the same small area hillshaded with the GDAL tools. Looks good, but \
> > > suffers from the same artifacts.  
> > 
> > No this is way it should look like (Image under).  You can see the pixels because \
> > you are zoomed in.  Again, select the correct z factor (if x,y are in long -lat \
> > and z is in meters or feet.) (probably ok here). 
> > <06.jpeg>
> > > 
> > > 
> > > 
> > Play with the resampling zoomed out parameters in symbology 
> > 
> > 
> > > 7) The larger area from hillshade in GDAL tools. 
> > > 
> > <07.jpeg>
> > > 
> > > 
> > > 
> > > 
> > > 
> > > I sorry to be so insisting on the problem, I think it is not the problem of \
> > > QGIS, but perhaps there are solutions to such a case. -- The projection is OK, \
> > > and the base map fits perfectly.  
> > > Best and Thanks to anyone trying to help, 
> > > Maria
> > > 
> > > 
> > > 
> > > 

_______________________________________________
Qgis-user mailing list
Qgis-user@lists.osgeo.org
List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user

[prev in list] [next in list] [prev in thread] [next in thread] 