[Spice_discussion] Geometry Engine
Terry Z. Martin
Terry.Z.Martin at jpl.nasa.gov
Wed Feb 19 10:24:26 PST 2003
Lee:
The below is all very nice for planning purposes, but does little (I
think) to deal with the reconstruction of geometry, in which case you
have the sampling time and some kernels, and need to get lat/lon,
distance, etc. etc. This is mentioned in your next-to-last paragraph.
I think the big advance there would come from providing template
software that could readily be adapted for an individual's needs. For
example, we took the Galileo PPR software that Nate Bachman helped us
with (extensively) and adapted it for use with Mars Global Surveyor
(where Boris did a lot of additional work). There is nothing like a
good sample program! You can read SPICE documentation until you are
blue in the face, but give me a sample every time.
Terry
PS. I would be happy to supply the code that we used on GLL and MGS.
>As part of an ongoing effort to increase the functionality of the
>SPICE Toolkit, we at NAIF are planning the development of SPICELIB
>routines that will allow the user to determine time windows or
>"schedules" when certain geometric constraints are met. To make this
>development process as efficient as possible, we'd like to determine
>which geometric constraints would offer the most "bang for the buck"
>in terms of useful functionality. Listed below are brief
>descriptions of what we've come up with (in a loose arrangement of
>decreasing priority):
>
>1)"Distance" -- determine time intervals during which the apparent
>distance between 2 specified bodies, as viewed from a specified
>observing body, satisfies a specified constraint (e.g. less than,
>equal to, greater than, between values)
>
>2)"Phase"-- determine time intervals during which the apparent
>observer-target-Sun angle satisfies a specified constraint.
>
>3)"Eclipse"-- determine time intervals during which one body is
>eclipsed by another as viewed by an observer.
>
>4)"Occultation/transit"-- determine time intervals during which one
>body is occulted/transited by another as viewed by an observer.
>
>5)"Time from periapsis/apoapsis"-- determine time intervals during
>which a body in orbit is within a specified time interval from
>periapsis/apoapsis.
>
>6)"Elevation"-- determine time intervals during which the elevation
>of an object, in a specified reference frame, satisfies a specified
>constraint.
>
>7)"Viewed Latitude/longitude"-- determine time intervals during
>which a viewed location (latitude/longitude) satisfies a specified
>constraint.
>
>8)"Nadir separation"-- determine time intervals during which the
>angle between an observed object and the nadir direction satisfies a
>specified constraint.
>
>9)"Separation"-- determine time intervals during which the angular
>separation of 2 bodies (as seen by an observer) satisfies a
>specified constraint.
>
>10)"Incidence/emission/solar longitude"-- determine time intervals
>during which the incidence/emission/solar longitude angle satisfies
>a specified constraint.
>
>11)"Orbital longitude"-- determine time intervals during which the
>orbital longitude of an object, relative to an observer, satisfies a
>specified constraint.
>
>12)"Angular velocity"-- determine time intervals during which the
>angular velocity of one object relative to another satisfies a
>specified constraint.
>
>13)"Apparent diameter"-- determine time intervals during which the
>apparent diameter of a body satisfies a specified constraint.
>
>14)"Elongation"-- determine time intervals during which the
>elongation (angular separation of a body from the sun) of a body
>satisfies a specified constraint.
>
>15)"Relative velocity"-- determine time intervals during which the
>velocity of one body relative to another satisfies a specified
>constraint.
>
>16) "User supplied"-- determine time intervals during which a
>function provided by the user satisfies a specified constraint.
>
>In addition to the time oriented "windows/schedules" discussed
>above, it is possible (but more work) to have other solutions. An
>example might be to find a range of viewed latitudes and longitudes
>for a specified time window.
>
>The main purpose of this note is to solicit your input. Are the 16
>constraints listed above of any use to you? Are there others that
>would be more useful?
>
>Regards,
>Lee Elson
>Lee.Elson at jpl.nasa.gov
>818-354-4223
>
>
>
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--
===================================================================
Dr. Terry Z. Martin 818 354-2178
Research Scientist fax: 393-4619
Earth and Planetary Atmospheres Terry.Z.Martin at jpl.nasa.gov
Jet Propulsion Lab 4800 Oak Grove Dr.
Mail stop 169-237 Pasadena CA 91109
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