[pdal] Calculation of the difference between DSM and DTM
Andrew Bell
andrew.bell.ia at gmail.com
Tue Jun 25 10:11:42 PDT 2024
The window size is different between pipelines. Don't know if that matters.
Also, there's nothing that prevents ground points above some first return
points in a cell. Maybe you want "min" mode for ground points and "max"
mode for first returns? Also, there's nothing here that matches up points
-- you could be using a first return from one location and a ground return
from another. Not sure what that would yield. Perhaps this needs something
more complex.
On Tue, Jun 25, 2024 at 10:38 AM Connor Manning <connor at hobu.co> wrote:
> Can you provide the file nubeRecortadaPdal_1.laz?
>
> On Tue, Jun 25, 2024 at 9:30 AM Raúl Casado Barbero
> <raul.casado at eez.csic.es> wrote:
> >
> > Hello Andrew,
> >
> > yes I'm sure. In fact I have some specific nodata pixels in DTM but the
> negative values in the difference cover almost the entire image.
> >
> > I'm using QGIS to substract both rasters using Raster calculator and
> GDAL Raster calculator but I get identical result.
> >
> >
> > El 25/06/2024 a las 15:58, Andrew Bell escribió:
> >
> > Hi Raul,
> >
> > Are you sure you're not seeing places where you have NODATA in one
> raster or the other?
> >
> > On Tue, Jun 25, 2024 at 2:09 AM Raúl Casado Barbero <
> raul.casado at eez.csic.es> wrote:
> >>
> >> Hi,
> >>
> >> thank you both. Imodified the pipeline adding origin_x, origin_y, width
> >> and height and now I get consistency inthe new rasters.
> >>
> >> The problem is that I still get negative values when I substract the MDT
> >> to MDS. Could it be due to interpolation in the calculation of MDT? If I
> >> get this raster by filtering the vegetation, could it be that values
> >> lower than MDS appear in areas where there is vegetation?
> >>
> >>
> >> Greetings.
> >>
> >> El 20/06/2024 a las 16:51, Connor Manning escribió:
> >> > For general information on how pipelines work:
> >> > https://pdal.io/en/2.7-maintenance/pipeline.html
> >> > And here is the information on the GDAL writer specifically, take a
> >> > look at origin_x and origin_y:
> >> >
> https://pdal.io/en/2.7-maintenance/stages/writers.gdal.html#writers-gdal
> >> >
> >> > For your pipelines, the GDAL writer is independently choosing its own
> >> > grid each time since you have not specified an origin, so the pixels
> >> > don't line up between the two outputs. You want to explicitly set the
> >> > same origin, via the above options, for both of your writers.gdal
> >> > outputs to make sure they line up.
> >> >
> >> > - Connor
> >> >
> >> > On Thu, Jun 20, 2024 at 8:36 AM Raúl Casado Barbero via pdal
> >> > <pdal at lists.osgeo.org> wrote:
> >> >> Hi Andrew and thaks for your answer.
> >> >>
> >> >> I'm pretty new with pdal just now and I'm tryingn to understand the
> logic of pipelines... What do you mean with set the origin on writers.gdal?
> >> >>
> >> >>
> >> >> Raúl.
> >> >>
> >> >> El 20/06/2024 a las 13:45, Andrew Bell escribió:
> >> >>
> >> >> Hi Raul,
> >> >>
> >> >> You should set the origin on writers.gdal in order to get the
> consistency you desire. Without this, the origin is set according to the
> first point processed, which may differ between pipelines.
> >> >>
> >> >> On Thu, Jun 20, 2024 at 4:24 AM Raúl Casado Barbero via pdal <
> pdal at lists.osgeo.org> wrote:
> >> >>> Hi,
> >> >>>
> >> >>> my aim is to calculate the fitovolume of a shrub vegetation area.
> To do that I calculate the DSM, classify a point cloud with ground (2) and
> low vegetation (3) and then create a DTM.
> >> >>>
> >> >>> I use 2 different pipelines (see below) to do that modified from
> this post. But I have 2 issues:
> >> >>>
> >> >>> When I calculate the difference between DSM and DTM I get negative
> values
> >> >>> The pixels of the DTM are horizontally displaced with respect to
> the DSM by half a pixel.
> >> >>>
> >> >>> Does anyone know why I am getting these negative values using this
> pipelines? Is anything wrong in the pipelines I`m using?
> >> >>>
> >> >>>
> >> >>> Raúl.
> >> >>>
> >> >>> Pipeline for DSM:
> >> >>>
> >> >>> [
> >> >>> "nubeRecortadaPdal_1.laz",
> >> >>> {
> >> >>> "type": "filters.range",
> >> >>> "limits":"returnnumber[1:1]"
> >> >>> },
> >> >>> {
> >> >>> "type": "writers.gdal",
> >> >>> "filename": "nubeRecortadaPdal_1_mds.tif",
> >> >>> "output_type": "idw",
> >> >>> "gdaldriver": "GTiff",
> >> >>> "resolution": 0.05,
> >> >>> "nodata": -9999,
> >> >>> "radius": 0.07,
> >> >>> "window_size": 50,
> >> >>> "data_type": "float32"
> >> >>> }
> >> >>> ]
> >> >>>
> >> >>> Pipeline for DTM:
> >> >>>
> >> >>> [
> >> >>> "nubeRecortadaPdal_1.laz",
> >> >>> {
> >> >>> "type":"filters.overlay",
> >> >>> "dimension":"Classification",
> >> >>> "datasource":"D:/Datos/clasificadasVector.gpkg",
> >> >>> "layer":"ndviRandomForest",
> >> >>> "column":"Id"
> >> >>> },
> >> >>> {
> >> >>> "type":"filters.range",
> >> >>> "limits":"Classification[2:2]"
> >> >>> },
> >> >>> {
> >> >>> "type": "writers.gdal",
> >> >>> "filename": "nubeRecortadaPdal_1_mdt_ndviRf.tif",
> >> >>> "output_type": "idw",
> >> >>> "gdaldriver": "GTiff",
> >> >>> "resolution": 0.05,
> >> >>> "nodata": -9999,
> >> >>> "radius": 0.07,
> >> >>> "window_size": 100,
> >> >>> "data_type": "float32"
> >> >>> }
> >> >>> ]
> >> >>>
> >> >>>
> >> >>> _______________________________________________
> >> >>> pdal mailing list
> >> >>> pdal at lists.osgeo.org
> >> >>> https://lists.osgeo.org/mailman/listinfo/pdal
> >> >>
> >> >>
> >> >> --
> >> >> Andrew Bell
> >> >> andrew.bell.ia at gmail.com
> >> >>
> >> >> --
> >> >> Raúl Casado Barbero
> >> >> Servicio de Evaluación, Restauración y Protección de Agrosistemas
> Mediterráneos
> >> >> Estacion Experimental del Zaidin, CSIC
> >> >> Calle Profesor Albareda 1, 18008 Granada, Spain
> >> >> Phone: +34 958181600 VolP CSIC 439186
> >> >>
> >> >> _______________________________________________
> >> >> pdal mailing list
> >> >> pdal at lists.osgeo.org
> >> >> https://lists.osgeo.org/mailman/listinfo/pdal
> >>
> >> --
> >> Raúl Casado Barbero
> >> Servicio de Evaluación, Restauración y Protección de Agrosistemas
> Mediterráneos
> >> Estacion Experimental del Zaidin, CSIC
> >> Calle Profesor Albareda 1, 18008 Granada, Spain
> >> Phone: +34 958181600 VolP CSIC 439186
> >>
> >
> >
> > --
> > Andrew Bell
> > andrew.bell.ia at gmail.com
> >
> > --
> > Raúl Casado Barbero
> > Servicio de Evaluación, Restauración y Protección de Agrosistemas
> Mediterráneos
> > Estacion Experimental del Zaidin, CSIC
> > Calle Profesor Albareda 1, 18008 Granada, Spain
> > Phone: +34 958181600 VolP CSIC 439186
>
--
Andrew Bell
andrew.bell.ia at gmail.com
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