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Re: cgmap_gshhs.pro minarea issue [message #86595 is a reply to message #86594] Thu, 21 November 2013 16:33 Go to previous messageGo to previous message
David Fanning is currently offline  David Fanning
Messages: 11724
Registered: August 2001
Senior Member
pvelissariou@fsu.edu writes:

> Apparently, in the recent versions (>= 2.2) of gshhs database
> the units of the header.area changed from 1/10 km^2 to 1/10 m^2.
> For cgmap_gshhs to work properly the line:
> polygonArea = header.area * 0.1 (ok for gshhs < 2.2)
> should be changed to:
> polygonArea = header.area * 1.0e-7 (for gshhs >= 2.2)

Here is what the creators of the data base say:

"The area of small (< 0.1 km^2) polygons got truncated to 0.
This would cause gshhs to consider them as lines (borders or
rivers) instead of polygons. Furthermore, the areas were
recomputed using the WGS-84 ellipsoid as the previous
area values were based on a spherical calculation. Thanks
to José Luis García Pallero for pointing this out. We now
store the area with a magnitude scale tuned to each polygon."

I don't really know what "tuned to each polygon" means, but I'm not
convinced it means what you seem to think it means.

Does anyone else know anything about this?

Cheers,

David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
Sepore ma de ni thue. ("Perhaps thou speakest truth.")

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