[pdal] Calculation of the difference between DSM and DTM

[Raúl Casado Barbero]

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 <https://github.com/manaakiwhenua/pycrown/issues/18>.
>     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"
>         }
>     ]
>
>
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>
>
>
> -- 
> 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
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