[gdal-dev] Gdal_grid and lake bathymetry

[Rahkonen Jukka (MML)]

Hi,

I have converted depth points of a small lake into tab separated CSV and I have generated surface, created contours and now I have an amusing plot of something 😊. I am somewhat lost with projections and actually everything but I think it is better to continue the discussion in the GMT Q&A forum. I will be there next week.

-Jukka-

-----Alkuperäinen viesti-----
Lähettäjä: Joaquim Manuel Freire Luís <jluis at ualg.pt> 
Lähetetty: torstai 21. marraskuuta 2019 21.42
Vastaanottaja: Rahkonen Jukka (MML) <jukka.rahkonen at maanmittauslaitos.fi>; gdal-dev at lists.osgeo.org
Aihe: RE: [gdal-dev] Gdal_grid and lake bathymetry

Jukka,

GMT will have the ability to read ogr formats (code for that is already in base but need to convert to GMT internal data representation and that is far from trivial). Meanwhile, if needed, just use ogr2ogr to convert your data to plain ascii x y z files (binary data is good as well) and feed it surface.

Joaquim

-----Original Message-----
From: Rahkonen Jukka (MML) <jukka.rahkonen at maanmittauslaitos.fi>
Sent: Thursday, November 21, 2019 4:22 PM
To: Joaquim Manuel Freire Luís <jluis at ualg.pt>; gdal-dev at lists.osgeo.org
Subject: VS: [gdal-dev] Gdal_grid and lake bathymetry

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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