[Spice_discussion] Modification to Icy functionality

[Ed Wright]

To: Icy Users
From: Ed Wright

I modified the behavior of Icy with regards to pre-initialized output 
values.

As of Icy 1.1, if you initialize a variable of the same type and size 
as an output argument, then use that variable as a return argument in a 
call, but the the call does not write to that variable, the variable 
returns to the IDL interpreter unmodified - a pass through.

As of Icy 1.2, Icy will create new memory for all output variables, 
regardless of their previous state. An unmodified output will return as 
zero, a zero vector, or zero array.

An example:

    cspice_vprjpi, vin, projpl, invpl, vout, found

    CSPICE_VPRJPI calculates the vector in a specified plane that
    maps under orthogonal projection to a specified vector in
    another plane.

Currently, if 'found' returns false, the routine does not modify an 
existing 3vector 'vout'. In 1.2, 'vout' returns [0.d,0.d,0.d] if 
'found' returns false.

This change applies only to write-only output arguments. The behavior 
of input/output arguments, e.g. windows, remains the same.

As always,
Ed Wright
ed.wright at jpl.nasa.gov
1-818-354-0371

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