[pdal] DSM and DTM mismatch.

[Murray, Jon]

Many thanks for your help.

Jon.

From: Andrew Bell <andrew.bell.ia at gmail.com>
Sent: 20 August 2018 14:25
To: Murray, Jon <j.murray3 at lancaster.ac.uk>
Cc: pdal at lists.osgeo.org
Subject: Re: [pdal] DSM and DTM mismatch.

Hi,

We haven't supported the p2g writer since version 1.5.  You should use writers.gdal instead.  Also, you're reprojection filter is a no-op, as the input and output SRSs are identical.  If you're wanting to override the SRS of the input, you can use the "--readers.las.spatialreference" option.

Best,


On Mon, Aug 20, 2018 at 9:09 AM, Murray, Jon <j.murray3 at lancaster.ac.uk<mailto:j.murray3 at lancaster.ac.uk>> wrote:
Ah – apologies. My first post as I explained. As below:

DSM:

{
    "pipeline":[
        "input1.las",

        {
            "type":"filters.reprojection",
            "in_srs":"EPSG:27700",
            "out_srs":"EPSG:27700"
        },
                {
            "type":"filters.range",
            "limits":"returnnumber[1:1]"
        },
        {
            "type":"writers.p2g",
            "filename":"dsm1",
            "output_type":"idw",
            "output_format":"tif",
            "grid_dist_x":0.5,
            "grid_dist_y":0.5,
            "radius":5
        }

    ]
}

DTM
{
    "pipeline":[
         "input1.las",
        {
            "type":"filters.reprojection",
            "in_srs":"EPSG:27700",
            "out_srs":"EPSG:27700"
        },
                {
            "type":"filters.ground",
            "approximate":true,
            "max_window_size":10,
            "slope":1.0,
            "max_distance":1,
            "initial_distance":0.15,
            "cell_size":1.0,
            "extract":true,
            "classify":false
        },
        {
            "type":"writers.p2g",
            "filename":"dtm1",
            "output_type":"idw",
            "output_format":"tif",
            "grid_dist_x":0.5,
            "grid_dist_y":0.5
        }
    ]
}

And the CHM:

gdal_calc.py -A dtm1.idw.tif -B dsm1.idw.tif --calc="B-A" --outfile chm1.tif –overwrite

Regards,

Jon.

From: Andrew Bell <andrew.bell.ia at gmail.com<mailto:andrew.bell.ia at gmail.com>>
Sent: 20 August 2018 13:58
To: Murray, Jon <j.murray3 at lancaster.ac.uk<mailto:j.murray3 at lancaster.ac.uk>>
Cc: pdal at lists.osgeo.org<mailto:pdal at lists.osgeo.org>
Subject: Re: [pdal] DSM and DTM mismatch.

You should post pipelines to show how exactly you're creating the files.

On Mon, Aug 20, 2018 at 8:49 AM, Murray, Jon <j.murray3 at lancaster.ac.uk<mailto:j.murray3 at lancaster.ac.uk>> wrote:
Hello PDAL users,

This is my first post to you all, having just joined the mailing list, so I hope this post is appropriate. I have a problem that I hope there is a PDAL (or possibly GDAL) based solution for. I have created both DSM and DTM from LiDAR (.las) data, using the appropriate PDAL filters/writers etc. It all works well, however there is a slight mismatch in output file sizes.

The DSM comes out at (3069,1094) and the DTM at (3069,1092), from the same input.las file. This prevents the CHM from being created (GDAL side now) as of course, the dimensions must match. I have tried reprocessing the DSM/DTM and changing grid sizes x/y, but no success.

Can anyone recommend a solution to this problem please? In short what can I do to make the DTM/DSM sizes match?

Many thanks,

Jon.

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--
Andrew Bell
andrew.bell.ia at gmail.com<mailto:andrew.bell.ia at gmail.com>



--
Andrew Bell
andrew.bell.ia at gmail.com<mailto:andrew.bell.ia at gmail.com>
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