why is eccentricity of zero an error?

Jim Aanstoos (919) 541-6890 AANSTOOS%LOUIE at rcc.rti.org
Sun Jul 4 13:09:36 EDT 1993

Does anybody know why an eccentricity or flattening coefficient
of zero is considered an error?  It makes it impossible to define a
sphere of constant radius as one choice in the ellipsoid table.  I
notice that such a choice appears in the default ellipsoid table
($GISBASE/etc/ellipse.table) but is commented out.  If you un-
comment it and then run something that uses that table (like
m.datum.shift), it gives an error referring to that line.  The error
comes from function get_a_e2 in get_ellipse.c of libes/gis, which
complains if the eccentricity (squared) or flattening value is
(less than or) equal to zero.  Should that test be changed to
less than zero only, or would that cause problems elsewhere?

      jim  /--\
          /    \ 
Jim Aanstoos                      Internet: aanstoos%louie at rcc.rti.org
                                         or aanstoos%louie at rti.rti.org
Research Triangle Institute                                           
PO Box 12194                                       Phone: 919-541-6890
Research Triangle Park, NC 27709-2194                Fax: 919-541-6515

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