Solving the coordinate precision problems in WorldWind

This posting is meant to store away relevant material for solving the coordinate system precision problems in WorldWind. It's written for me as notes for me, but maybe it will help you!

#1 -- Statement of problem:

• http://issues.worldwind.arc.nasa.gov/browse/WW-76
• http://issues.worldwind.arc.nasa.gov/browse/WW-477
• http://www.terrainmap.com/rm45.html

#2 -- Problem manifestations

• "Jitter" at high resolution
• Poor Picking Rays -- difficulty with moving the camera in high res
• tiling naming output :

#3 -- Google search terms:

• worldwind jitter
• gamasutra jitter
• global coordinate scenery jitter
• Heizenberg range
  

#4 -- Possible solutions / Problem discussions

• http://www.surak.com.au/~chris/PrecisionInVRML/PrecisionInVRML.htm for the same issue in GeoVRML
• nhv suggestion: FlightGear, http://www.flightgear.org
• http://www.blitzcoder.com/cgi-bin/ubb-cgi/postdisplay.cgi?forum=Forum4&topic=000352
• http://planet-earth.org/cw05/FloatingOrigin.pdf
• http://www.gamasutra.com/features/20020712/oneil_01.htm##
• http://www.ai.sri.com/~reddy/geovrml/double/
• http://pastebin.com/527915 -- ddh's recent work (splitting lat SP into two separate values -- haven't evaluated yet)
• http://www.gameprogrammer.com/4-fixed.html
• http://java.sun.com/products/java-media/3D/forDevelopers/J3D_1_2_API/j3dguide/VirtualUniverse.doc.html#49034
• http://www.surak.com.au/~chris/PrecisionInVRML/SinglePrecisionGeoVRML.html
• http://sourceforge.net/projects/retinax/ and http://sourceforge.net/forum/forum.php?forum_id=523573 for scene graphs
• If someone is interested, Celestia has already solved this problem. I don't know specifically how they do it, but apparently, they are able to render a "BigInt" or something that is the equivalent of a 128 or 256-bit number. I'm going to assume it's the manipulation of the Matrix stack from global to local coordinate systems.
• Look at Worldwind logs for 5-26-2005, 5-27-2005, 5-28-2005

#5 -- Methods:

• Force Camera at 0,0,0 -- get the most precision possible.
• Localized camera coordinate space - e.g. shift the mantissa at established camera positions
• Doublize by methods in above locations (although, alledgedly, this is quickly runs out too).
• Doublize by software-based vp (ugh)
• Add a decimal camera position, at least compute picking rays on decimal. Solve the jitter by forcing consistent roundoff error, or weighting based on altitude
• Perhaps force a localized zclipping that is more impervious (search on imposters)
• Finish reading items in #4 for more alternatives.

#6 -- My solution:

• My personal solutions was constrained by: a) lack of time, and b) desire to impact the Worldwind code base to the least amount possible (I hate branching and merging).
• Thus I have gone with a localized solution that bumps up the coordinate projection system by several powers of two after a certain altitude is reached. This allows me to preserve adequate precision. It of course has ramifications throughout worldwind code, but I think I've gotten it fairly managed. I still need more testing to see if additional tweaks are necessary.