[pdal] Calculation of the difference between DSM and DTM
Andrew Bell
andrew.bell.ia at gmail.com
Wed Jun 26 06:10:54 PDT 2024
I don't think it's reasonable to debug this as present. I would do a few
things to make progress:
1. Find a cell that you think is in error.
2. Filter the data to only contain points in that cell.
3. Make sure the results from the overlay filter are what you expect.
4. Look at statistics for the points and verify the behavior by hand.
On Wed, Jun 26, 2024 at 3:01 AM Raúl Casado Barbero <raul.casado at eez.csic.es>
wrote:
> Hello,
>
> sure, here it is.
>
>
> https://drive.google.com/file/d/1u0OxHek6NqRO4g396xOlBT_CGwFCyplN/view?usp=sharing
>
>
> El 25/06/2024 a las 16:38, Connor Manning escribió:
> > 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
>
> --
> 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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