Re: [Opengc-devel] fix database?

[Damion S. <da...@op...>]

Hi,

> In the Navigation directory, the NavDatabase::InitDatabase loads
> nav.dat and apt.dat.  There seems to be some files related to
> fixes (ogcFixGeographicObject.cpp), but they don't seem to be
> written.  Are these works in progress?

Yes, they're works in progress. Basically, I wrote a simple parser that 
reads in the X-Plane format nav database stuff and one of the X-Plane 
nav files was "fix.dat". I ran into a few problems that halted nav 
database development:

1) The X-Plane database contains kludges to make the data work well in 
X-Plane's somewhat odd world representation. This makes me skeptical 
that the data could be relied on for real-world navigation.

2) I was using a Mercator map project, which is substantially less than 
ideal. I'm developing a lambert conformal conic projection with the 
idea that I can also load in the rasterized sectional charts in geotiff 
format from the FAA, but this is still vaporware at this point.

3) The entire nav project got put on hold because of the data source 
rewrite, which I just finished (using the term finished loosely) a week 
ago.

> Shouldn't the fixes be
> similar to the navaids and airports?  Or are there just too many
> of them defined?  What is the status of these files?

There's no fundamental limit to the amount of navigation data OpenGC 
can hold. The data itself is relatively compact, the main challenge is 
hashing the data in a reasonable way so that only the local area needs 
to be rendered. I was chunking the data into 1x1 degree bins, which 
worked reasonably well but could no doubt be improved quite a bit. To 
answer your first question, yes, the fixes would be quite similar to 
airports and navaids. They're actually about as simple as you can get: 
a lat/lon coordinate pair and a text identifier.

After I finish updating all of the data source code the nav subsystem 
is the next "big thing" I'm going to tackle. If you have any feedback / 
suggestions / comments I'd appreciate hearing them.

Cheers,
Damion

---------
Damion Shelton
Carnegie Mellon University, Robotics Institute
A408-o Newell Simon Hall
412.268.3866 (office)
412.818.8829 (cell)
412.268.6436 (fax)
http://www.cs.cmu.edu/~beowulf
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