[pdal] Calculation of the difference between DSM and DTM

[Andrew Bell]

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
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