I wonder if it would make sense to talk about some of this stuff with Steve Hughes, CC’ed here, Martin. Steve, meet Martin Desruisseaux who is working on Apache SIS. Martin, meet Steve who is the Planetary Data System (PDS) System Engineer and a JPL principal. This sounds useful potentially to PDS.
Cheers, Chris ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Chris Mattmann, Ph.D. Chief Architect Instrument Software and Science Data Systems Section (398) NASA Jet Propulsion Laboratory Pasadena, CA 91109 USA Office: 168-519, Mailstop: 168-527 Email: [email protected] WWW: http://sunset.usc.edu/~mattmann/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Adjunct Associate Professor, Computer Science Department University of Southern California, Los Angeles, CA 90089 USA ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -----Original Message----- From: Martin Desruisseaux <[email protected]> Organization: Geomatys Reply-To: "[email protected]" <[email protected]> Date: Wednesday, October 28, 2015 at 4:29 PM To: Apache SIS <[email protected]> Subject: Note about usage of SIS for planets other than Earth >Hello all > >A note in case some peoples are interested in planetary mapping. Often, >the methods for going from Cartesian coordinates (e.g. map projection or >geocentric system) to geographic coordinates have no exact formulas. The >solution is approximated in various ways, but two common approaches are: > > * iteration until the error become sufficiently small, > * or series expansions. > >The series expansions are often preferred since they are faster than >iterations (at least twice faster for Lambert Conic Conformal according >my measurement) for equivalent precision. They can be found in the EPSG >guidance notes for instances, and their accuracy are quite good. However >precision of series expansions depend on the number of terms, and that >number is usually chosen for a planet having an eccentricity like Earth. >Empirical tests suggest that for a planet having an eccentricity twice >larger than Earth, series expansion precision become lower than iteration. > >Apache SIS currently focus about Earth. However I opportunistically made >some provisions for planetary usages when I could identify a possible >issue with high eccentricities. The strategy is: > > 1. Begin with series expansion. For geographic coordinates on Earth, > this is the only step. > 2. Only if we know that series expansion may not be enough (e.g. > eccentricity is above some threshold), continue with iteration. > >For Lambert Conic Conformal projection this was relatively easy. For the >"Geocentric to Geographic conversion" just committed today it is more >difficult, because the precision is impacted by two parameters: > > * high eccentricity (e) > * high altitude (h) > >I did not tried to resolve how those parameters interact with each >others. However if there is any peoples in this list who have an >interest for extraterrestrial planetary mapping, this is an area where >some research could be done. A first step could be to maintain a wiki >page listing known issues like this one. > > Martin > >
