id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
289	Support for simple simulated orbits	Dave Offiler	Ian Culverwell	"Helpdesk enquiry from Stephan Junker (UniBwM) 2/8/2012:

{{{
Hello,

I have simulated phase and amplitude measurements for RO events
with an adaption of the GFZ software ""simend2end"", which uses
analytical refractive profiles and turns them into phase
measurements by using inverse FSI. In parallel, the orbits of LEO
and GPS satellites (occ+ref) are simulated. The simulated orbit
move exclusively in the x,y plane and therefore the z-value for all
satellites is always '0.0'.

Now my question regarding the ropp-6.0 package. When I use the
ropp_pp_occ_tool the preprocessor is exiting the processing with
the statement: ""invalid coordinate values"". Is the described
satellite constellation the problem or are there other reasons for
this behaviour?

Thank you and kind regards,
Stefan Junker
}}}

After a quick look, my reply was:

{{{
Stefan,

This check and error message comes from the preprocessor source
code file:
  ropp_pp/preprocess/ropp_pp_preprocess.f90
and can be triggered by *any* X,Y,Z coordinate of the LEO *or* the
GPS satellite having a 'missing data' value. We'd need to trace
backwards to see which satellite(s), and which coordinate
component(s) have this special flag value, and why.

I suspect that if any single coordinate value over a profile is a
constant zero, this is assumed to be an error condition (it's
certainly not valid for real satellites!), but I don't know this
code well enough myself to be sure if this sort of test is done
(the author is on holiday at the moment...)

I do know for certain that if all three X,Y,Z values are zero, this
is a flag for the satellite location to be 'missing'

If possible, could you please try to:
(a) ensure that all 6 coord values are within sensible range (and
none are [0,0,0])
(b) set a non-zero Z-value (1.0 (metres) shouldn't make any
practical difference to the simulation)
(c) print out the 2 sets of coordinates (line 104 of the above
source code file - obviously this would mean re-compiling the
pre-process module)

ROPP wasn't designed for the orbits you are simulating, so we will
revisit the code to see if there are tests and/or assumptions that
can be relaxed to support your simulations (for a future release or
patch update), or if a simple data change (like not having
constant-zero coordinate values) might get past these checks.
}}}

Stephan later confirmed that setting his Z-values to 0.1m (my option (b) works, allowing the Helpdesk item to be closed.

So I would hazard that somewhere in the ROPP code, there's a check
for all X, Y or Z POD elements in a profile being zero (within some
tolerance), but is happy if all value are non-zero (even if identical.

We should now re-visit the code to decide whether this test can be relaxed, or merely that setting non-zero Z-values (or any POD element?) for simple simulated orbits should be noted in the UG."	task	closed	minor	6.1	ropp_pp	6.0	fixed	Orbits, simulated, checking