View Full Version : amount of inofrmation from one system to the other

technologist

11-02-2017, 03:04 PM

Hi, my question is very broad. I recently tried to understand a tutorial using polar coordinates in moving the camera about. The coordinate was described in (theta, radius). What I don't understand is theoretically how one can get more information from a lower information state: example, cartesian coordinates (x,y,z) from polar(theta,r). Please forgive any assumption that I may have violated, etc., the polar coordinate system is pretty new to me.:confused:

Also why would I want to use a polar system over s cartesian?

Silence

11-03-2017, 01:15 AM

Hi, my question is very broad. I recently tried to understand a tutorial using polar coordinates in moving the camera about. The coordinate was described in (theta, radius). What I don't understand is theoretically how one can get more information from a lower information state: example, cartesian coordinates (x,y,z) from polar(theta,r). Please forgive any assumption that I may have violated, etc., the polar coordinate system is pretty new to me.:confused:

Also why would I want to use a polar system over s cartesian?

In 3D, for polar coordinates you need another dimension: the elevation angle, generally named phi. So you have (r, theta, phi) which allows you to orientate on a unit sphere and to place at whatever radius. Which is similar to a cartesian vector v (x,y,z), which, from the origin, allows you to place wherever on the unit sphere as well (x/magnitude(v),x/magnitude(v),z/magnitude(v)) and at whatever distance from it (the magnitude of the vector).

technologist

11-03-2017, 02:49 PM

Thank you for the reply:

When considering gluLookAt(Eyex,Eyey,Eyez,Targetx, Ty,Tz, 0,1,0) is gluLookAt navigation-specific? In other words is gLA natively polar, or, cartesian, or both?

Thx in advance

technologist

11-03-2017, 03:39 PM

Thank you for the reply:

When considering gluLookAt(Eyex,Eyey,Eyez,Targetx, Ty,Tz, 0,1,0) is gluLookAt navigation-specific? In other words is gLA natively polar, or, cartesian, or both?

Thx in advance

Sorry, troubles with forum.

Secondly (in addition to above), when polar coordinates are changing on keystroke by keystroke input, are the position results aggregated to a sum total frame by frame, or are the position results always calculated from the same origin point e.g. 0,0,0 within a unit circle and multiplied by radii (vector magnitude if cartesian)? Sorry if the descriptions are rough and inaccurate.

Thx in advance

GClements

11-04-2017, 10:17 AM

When considering gluLookAt(Eyex,Eyey,Eyez,Targetx, Ty,Tz, 0,1,0) is gluLookAt navigation-specific? In other words is gLA natively polar, or, cartesian, or both?

Cartesian. The eye, target and up vectors have to use Cartesian coordinates. If you had polar coordinates, you'd either convert them to Cartesian coordinates or use a combination of glRotate and glTranslate.

GClements

11-04-2017, 10:20 AM

Secondly (in addition to above), when polar coordinates are changing on keystroke by keystroke input, are the position results aggregated to a sum total frame by frame, or are the position results always calculated from the same origin point e.g. 0,0,0 within a unit circle and multiplied by radii (vector magnitude if cartesian)?

You might implement an orbital camera by accumulating changes to polar coordinates. Other than that, polar coordinates are rarely used; most things are much simpler with cartesian coordinates. E.g. if you're navigating on a sphere, you'd either use geocentric Cartesian coordinates, or a projected coordinate system (Mercator or whatever).

technologist

11-05-2017, 05:23 PM

Thank you for all the answers. Very helpful.

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