[GRASSLIST:3190] bathymetry

Ian Macmillan ian_macmillan at umail.ucsb.edu
Fri Apr 16 03:58:59 EDT 2004

Hi all, I have been attempting to import the Smith and Sandwell worldwide
bathymetry map, and have been having a lot of difficulty.  The data comes as a
mercator projected file on a sphere with coordinates in latitude and longitude.
 I know the number of rows and columns, and the bounding coordinates (in
lat-long).  How can I import this entire data set?  

I tried to import it in many different locations and projecting among them,
latlong, merc, xy (and then projecting into latlong).  All of them end up
giving me an image that is not georeferenced correctly.  It is usually close,
but it does not line up well with GTOPO30 data, or digital chart of the world
data.  I have been using GRASS for a couple of years now, and am pretty
comfortable with it, but I don't have any idea what I am doing wrong.  I am
making sure that the projection parameters are correct (ellipsoid=sphere), but
it seems like a projection problem with the slight offset of the data.

I also tried to use img2mercgrd and grd2xyz in GMT and then tried to import the
data as an ascii file.  Again, the data is offset.  I have used this data in
conjunction with GTOPO30 data in GMT, so I know that they really do line up.  

Has anyone else imported this data into GRASS, and if so, could you tell me how
you did it?  

Thanks, Ian

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