[GRASS-user] Help with creating bathymetric maps

[Brent Wood]

Hi Alyre,

In the maritime community, I think GMT )Generic Mapping Tools: http://gmt.soest.hawai.edu) is more widely used than GRASS, espacially for publication quality map output.

It has very effective tools for generating & manipulating grids (DEMs) & both plotting contours directly from the grid (optionally smoothed - perhaps useful for your 0 contour) & generating contours as vectors from them.
OGR (ogr2ogr) can convert to/from GMT vectors, & with some fiddling, it can also create GMT grids from other rasters, although you may find ir easier to work entirely with GMT & to generate your grid in GMR from your source point data.

If you are interested, send me the original data and I can scribble out a quick script to demonstrate this...

Cheers,

  Brent Wood 


Brent Wood
DBA/GIS consultant
NIWA, Wellington
New Zealand
>>> Alyre <alyre.chiasson at umoncton.ca> 05/15/09 5:46 AM >>>

Hello,

I am trying to create a bathymetric map of a small pond. I have imported the
depths and  digitized the outline of the shore (0 depth contour). I believe
in GRASS both would by default be in vector format and I need to transform
them into raster and merge both files. I have successfully converted the
shoreline into raster form but it appears as a solid area as if the whole
polygon that enclosed the pond was transformed and not the outline. What I
need is to convert the outline of the polygon to a series of raster points
and be able to define the spacing. The spacing of the 0 contour points
appears to me to be important as it will influence the interpolation of the
contours when the transect depths are added. In addition I am not sure how
to assign the additional attribute of depth (which would be zero) in the
transformation process or how to add it afterwards. From what I understand
in GRASS, points are actually vectors but to do contours everything has to
be in raster format. So I assume I will have to convert the depths (x,y,z)
into raster format as well then merge the two raster files (shore outline of
zero depth with depth transects). 

I assume GRASS is widely used to do bathymetric maps, a bit like elevation
contours but with negative values. If anyone knows of a tutorial or step by
step guidance at a beginner's level that would be most helpful. The
bathymetric map is only a support element of a large fish distribution study
but is turning out to be much more difficult to achieve than expected.

Thanks

Alyre
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