[gdal-dev] Gdal_grid and lake bathymetry

[Jan Hartmann]

These are important options. It would be nice if they could be 
implemented in gdal_grid itself. Not sure how difficult that would be, 
though.

Jan

On 11/21/2019 5:21 PM, Rahkonen Jukka (MML) wrote:
> Hi Joaquim,
>
> GMT surface probably has all the features that I need. I followed the tutorial and managed to run surface demos, now I just need to learn how to use my own data as input.
>
> -Jukka-
>
> -----Alkuperäinen viesti-----
> Lähettäjä: Joaquim Manuel Freire Luís <jluis at ualg.pt>
> Lähetetty: keskiviikko 20. marraskuuta 2019 0.30
> Vastaanottaja: Even Rouault <even.rouault at spatialys.com>; gdal-dev at lists.osgeo.org
> Kopio: Rahkonen Jukka (MML) <jukka.rahkonen at maanmittauslaitos.fi>
> Aihe: RE: [gdal-dev] Gdal_grid and lake bathymetry
>
> The GMT surface program has two (well 3) options that are of interest to this.
>
> -One, the -Lu<upper> that serves to limit the upper value in the interpolated grid
>
> -The other is the option -D that lets you set a soft-breakline (your shorelines). Soft-breaklines are lines whose vertex end up in the grid nodes closest to them. They are called "soft" in contraposition to the hard-breaklines that do not let the interpolation algorithm go across them. Imagine interpolation a terrain with vertical cliffs. Unfortunately that -D option is missing on the html man page but is described on the surface on line help.
>
> -Finally, option -M lets you mask the outside lakes region
>
> https://docs.generic-mapping-tools.org/latest/surface.html
>
> Joaquim
>
> -----Original Message-----
> From: gdal-dev <gdal-dev-bounces at lists.osgeo.org> On Behalf Of Even Rouault
> Sent: Tuesday, November 19, 2019 10:13 PM
> To: gdal-dev at lists.osgeo.org
> Cc: Rahkonen Jukka (MML) <jukka.rahkonen at maanmittauslaitos.fi>
> Subject: Re: [gdal-dev] Gdal_grid and lake bathymetry
>
> On mardi 19 novembre 2019 22:03:29 CET Rahkonen Jukka (MML) wrote:
>> Hi,
>>
>> I would like to get some hints about using gdal_grid or some other
>> utility for lake bathymetry. What I have is typically rather sparse
>> point data of depths and the shoreline that includes the islands as in
>> the attached image. The shoreline and all the area that is not lake
>> basin should have the altitude of zero in the resulting DEM. It means
>> that interpolation should not overshoot across the shoreline over the dry land.
>>
>> Gdal_grid seems to miss an option for handling the shoreline so I made
>> a test by converting the vertices of the polygon rings into depth
>> points. I also filled area around the lake with a gridded points of
>> zero altitude but the method feels stupid and tedious and the result
>> was not so fine when it comes to keep the shoreline and land area near it totally flat.
>>
> Postprocessing with gdalwarp -cutline to set to zero non-lake areas ?
>
> --
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