[gdal-dev] Gdal_grid and lake bathymetry

[Rahkonen Jukka (MML)]

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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