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    <p>Hi,</p>
    <p>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.</p>
    <p>I use 2 different pipelines (see below) to do that modified from
      <a href="https://github.com/manaakiwhenua/pycrown/issues/18">this
        post</a>. But I have 2 issues:</p>
    <ul>
      <li>When I calculate the difference between DSM and DTM I get
        negative values</li>
      <li>The pixels of the DTM are horizontally displaced with respect
        to the DSM by half a pixel.</li>
    </ul>
    <p>Does anyone know why I am getting these negative values using
      this pipelines? Is anything wrong in the pipelines I`m using?<br>
      <br>
      <br>
      Raúl.<br>
      <br>
      Pipeline for DSM:<br>
      <br>
      [<br>
          "nubeRecortadaPdal_1.laz",<br>
          {<br>
              "type": "filters.range",<br>
              "limits":"returnnumber[1:1]"<br>
          },<br>
          {<br>
              "type": "writers.gdal",<br>
              "filename": "nubeRecortadaPdal_1_mds.tif",<br>
              "output_type": "idw",<br>
              "gdaldriver": "GTiff",<br>
              "resolution": 0.05, <br>
              "nodata": -9999,<br>
              "radius": 0.07,<br>
              "window_size": 50,<br>
              "data_type": "float32"<br>
          }<br>
      ]<br>
      <br>
      Pipeline for DTM:<br>
      <br>
      [<br>
          "nubeRecortadaPdal_1.laz",<br>
          {<br>
              "type":"filters.overlay",<br>
              "dimension":"Classification",<br>
              "datasource":"D:/Datos/clasificadasVector.gpkg",<br>
              "layer":"ndviRandomForest",<br>
              "column":"Id"<br>
          },<br>
          {<br>
              "type":"filters.range",<br>
              "limits":"Classification[2:2]"<br>
          },<br>
          {<br>
              "type": "writers.gdal",<br>
              "filename": "nubeRecortadaPdal_1_mdt_ndviRf.tif",<br>
              "output_type": "idw",<br>
              "gdaldriver": "GTiff",<br>
              "resolution": 0.05, <br>
              "nodata": -9999,<br>
              "radius": 0.07,<br>
              "window_size": 100,<br>
              "data_type": "float32"<br>
          }<br>
      ]</p>
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