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## Re: [Stellarium-pubdevel] Question on StelProjector::unProject

 Re: [Stellarium-pubdevel] Question on StelProjector::unProject From: Timothy Reaves - 2009-05-12 20:01:49 ```On May 12, 2009, at 9:34 AM, Fabien Chéreau wrote: > Hi, > The 3 values are the Cartesian X, Y and Z values of a direction > vector. They have no unit because it depends on the current projection > matrix used. > For example if you use the J2000 frame, the direction will be in the > J2000 frame as seen from the observer. > Fabien I thought only two values were needed for this, and that typically the z value would represent distance? If I use the J2000 frame, dec would be one value, right asc the other, so what is the third? Thanks much for the info, and patience with all the questions! ```

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 [Stellarium-pubdevel] Question on StelProjector::unProject From: Timothy Reaves - 2009-05-12 14:03:32 ``` This fills in a Vec3d from an X & Y screen coordinate. What are the three values in the vector? What unit are they in? Reading the code, it looks like radians, but I'm not sure. I'm also not sure why there are three values. I'm sure a lot of this type of information is second-nature to some of you, but to people wanting to contribute, this type of information is needed. It'd be great to have a code FIX-IT around updating the code documentation. ```
 Re: [Stellarium-pubdevel] Question on StelProjector::unProject From: Fabien Chéreau - 2009-05-12 14:34:24 ```Hi, The 3 values are the Cartesian X, Y and Z values of a direction vector. They have no unit because it depends on the current projection matrix used. For example if you use the J2000 frame, the direction will be in the J2000 frame as seen from the observer. Fabien PS: I improved a bit the doc. On Tue, May 12, 2009 at 15:54, Timothy Reaves wrote: >        This fills in a Vec3d from an X & Y screen coordinate.  What are the > three values in the vector?  What unit are they in?  Reading the code, > it looks like radians, but I'm not sure.  I'm also not sure why there > are three values. > >        I'm sure a lot of this type of information is second-nature to some > of you, but to people wanting to contribute, this type of information > is needed.  It'd be great to have a code FIX-IT around updating the > code documentation. > > ------------------------------------------------------------------------------ > The NEW KODAK i700 Series Scanners deliver under ANY circumstances! Your > production scanning environment may not be a perfect world - but thanks to > Kodak, there's a perfect scanner to get the job done! With the NEW KODAK i700 > Series Scanner you'll get full speed at 300 dpi even with all image > processing features enabled. http://p.sf.net/sfu/kodak-com > _______________________________________________ > Stellarium-pubdevel mailing list > Stellarium-pubdevel@... > https://lists.sourceforge.net/lists/listinfo/stellarium-pubdevel > ```
 Re: [Stellarium-pubdevel] Question on StelProjector::unProject From: Timothy Reaves - 2009-05-12 20:01:49 ```On May 12, 2009, at 9:34 AM, Fabien Chéreau wrote: > Hi, > The 3 values are the Cartesian X, Y and Z values of a direction > vector. They have no unit because it depends on the current projection > matrix used. > For example if you use the J2000 frame, the direction will be in the > J2000 frame as seen from the observer. > Fabien I thought only two values were needed for this, and that typically the z value would represent distance? If I use the J2000 frame, dec would be one value, right asc the other, so what is the third? Thanks much for the info, and patience with all the questions! ```
 Re: [Stellarium-pubdevel] Question on StelProjector::unProject From: Fabien Chéreau - 2009-05-12 20:39:18 ```On Tue, May 12, 2009 at 22:01, Timothy Reaves wrote: > > On May 12, 2009, at 9:34 AM, Fabien Chéreau wrote: > >> Hi, >> The 3 values are the Cartesian X, Y and Z values of a direction >> vector. They have no unit because it depends on the current projection >> matrix used. >> For example if you use the J2000 frame, the direction will be in the >> J2000 frame as seen from the observer. >> Fabien > > >        I thought only two values were needed for this, and that typically > the z value would represent distance?  If I use the J2000 frame, dec > would be one value, right asc the other, so what is the third? The spherical RA/Dec representation of a direction is not very convenient for most usage because it involves trigonometry operations which are very slow. You can convert from one representation to the other using StelUtil::spheToRect family functions. >        Thanks much for the info, and patience with all the questions! You're welcome! I wish I had more time to help you guys. But I do follow the mailing list silently. Fabien ```