Stellarium

Tweeking AngleMeasure to display Alt/Az delta

Asked by Chris Rixon

I want to tweek AngleMeasure to display Alt/Az delta instead of a simple angle.

The idea is to drag the line between two stars and display and display the difference in altitude and azimuth between the stars.

AngleMeasure makes two Vec3d's: startPoint and endPoint

It looks like I need a StelNavigator object instead of a Vec3d and then Alt/Az is easy.

So my question is: can I convert a Vec3d into a StelNavigator?

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
More stuff.

The end goal is to create a "poor man's goto".

The idea is to strap a Iphone4 / Itouch4 (with gyroscope) to the scope.
I have a simple HTML5 "app" to display Alt/Az delta.
Align telescope with star1.
Use the plugin to calc Alt/Az delta between star1 and star2.
Move the telescope Alt/Az delta.
Telescope is pointing at star2.
voila!

Question information

Language:
English Edit question
Status:
Answered
For:
Stellarium Edit question
Assignee:
No assignee Edit question
Last query:
Last reply:
Revision history for this message
Bogdan Marinov (daggerstab) said : 		#1

What do you mean exactly by "Alt/Az delta"? A vector? How do you express it?

And by the way:
- Vec3d is a data structure - a vector defined by three double-precision values
- StelNavigator is a class that provides functions for transformation between different coordinate systems
By their very nature you cannot convert the former to the latter. :)

Revision history for this message
Chris Rixon (chrisrixon) said : 		#2

I just discovered that Azimuth is not what I thought and really I mean horizontal angle, duh.

See the picture here:

http://i51.tinypic.com/e8q3bq.gif

In this case I want to get from Pollux to Castor so I need the Horizontal angle and the vertical angle.

AngleMeasure makes two Vec3d's: startPoint (Pollux) and endPoint (Castor) so I'm hoping I can convert those vectors to the coordinates of the two stars as StelNavigator's and then extracting the HA and VA is easy(ish). Thanks :D

Revision history for this message
treaves (treaves) said : 		#3

Perhaps the easiest is to project the two points into screen coordinates, and handle them that way. Then the drawing becomes trivial, and the intersection point can be projected back into the sphere for determination of angle. Shouldn't be too hard.

Can you help with this problem?

Provide an answer of your own, or ask Chris Rixon for more information if necessary.

To post a message you must log in.