[pdal] [EXTERNAL] Re: DSM and DTM mismatch.

[Doug Newcomb]

Jon,
Try getting an xy extent of the 1st returns vsan xy extent of  just the
ground points.  It may be that the extent of the 1st returns is larger than
that of the ground returns at the 0.5 (m? ft?) scale.

Doug

On Mon, Aug 20, 2018 at 9:10 AM Murray, Jon <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>
> *Sent:* 20 August 2018 13:58
> *To:* Murray, Jon <j.murray3 at lancaster.ac.uk>
> *Cc:* 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>
> 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
>


-- 
Doug Newcomb - Cartographer
USFWS
551F Pylon Dr
Raleigh, NC
919-856-4520 ext. 14 doug_newcomb at fws.gov
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