[OSRS-PROJ] da, df

Felipe G. Nievinski fnievinski at terra.com.br
Sat Aug 4 19:30:49 EDT 2001

FYI (about the DA and DF parameters)

The DA and DF are the delta values between the ellipsoid used by WGS-84 and another given ellipsoid:
da = [a(WGS 84 ellipsoid) - a(second ellipsoid)] | a = semi-major (equatorial) axis
df = [f(WGS 84 ellipsoid) - f(second ellisoid)*10000] | f = flattening

They are commonly used by NAVSTAR-GPS receivers, which shall already know the WGS-84 model, and therefore needs less space to store just the delta values for the others Earth models than the a and f values themselves.
For example, the Finnish ellipsoid can be defined by:
da = -251 m
df = -0.14192702

hope this helps.

Felipe Nievinski.

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