[pdal] Crop SRS not working as expected

[Andreas Yankopolus]

All—

I’m cropping and processing USGS LPC data into WGS84 raster files, but I can’t get the cropping to work out correctly: My pdal crop stage specifies a square region in WGS8, but the resulting files display as rhombuses. Here’s a minimal example:

{
  "pipeline": [
    "/home/ayank/Documents/geodata/lpc/*.laz",
    {
      "type": "filters.crop",
      "bounds": "([-117.18,-117.13],[32.68,32.73])",
      "a_srs": "EPSG:4326"
    },
    {
      "type": "filters.range",
      "limits": "Classification[2:2]"
    },
    {
      "filename": "/home/ayank/Documents/geodata/export/sd_coord_test.laz",
      "type": "writers.las",
      "compression": "laszip",
      "extra_dims": "all"
    },
    {
      "filename": "/home/ayank/Documents/geodata/export/sd_coord_test.tiff",
      "type": "writers.gdal",
      "gdaldriver": "GTiff",
      "dimension": "Z",
      "output_type": "idw",
      "resolution": "10"
    }
  ]
}

My expectation is that the output files, when read into QGIS with WGS84 (EPSG:4326) as the project CRS, would render as squares. But they’re both a rhombus.

I’ve also tried adding these two stages to the pipeline:

    {
      "type": "filters.reprojection",
      "out_srs": "EPSG:4326"
    },

    {
      "filename": "/home/ayank/Documents/geodata/export/sd_coord_test_4326.tiff",
      "type": "writers.gdal",
      "gdaldriver": "GTiff",
      "dimension": "Z",
      "output_type": "idw",
      "resolution": "9.25925925925925925925925e-5"
    }

Running gdalinfo on the resulting TIFF shows it as not a square:

Size is 552, 541

Corner Coordinates:
Upper Left  (-117.1805780,  32.7300307) (117d10'50.08"W, 32d43'48.11"N)
Lower Left  (-117.1805780,  32.6799381) (117d10'50.08"W, 32d40'47.78"N)
Upper Right (-117.1294669,  32.7300307) (117d 7'46.08"W, 32d43'48.11"N)
Lower Right (-117.1294669,  32.6799381) (117d 7'46.08"W, 32d40'47.78"N)
Center      (-117.1550224,  32.7049844) (117d 9'18.08"W, 32d42'17.94”N)

It overlaps with the previous two output files perfectly.

What am I doing wrong?

My thinking has been to keep the LPC data in its original CRS to avoid dealing with scaling factors and offsets. It appears to combine NAD83 and survey feet.

Thanks,

Andreas
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