Celestia Forums

whats the difference of the Sync and Chase commands???

does anybody know????

Chase ?

did you meen Follow, or Centre. ?

follow will follow the planets Orbit and watch it rotate
and sync will rotate with the planets orbit.

if this is what you are asking. ?

In Sync mode the referential is locked to the object's rotation. You stay above the same location of the object.

In Chase mode the referential is locked to the body's velocity vector. Sync and Chase are very different. Chase is more similar to a Lock mode with the parent body if the orbit is not too excentric.

Sync with Earth:
cel://SyncOrbit/Sol:Earth/2003-06-20T04:43:25.48563?x=UNmWFpHhcTq9DA&y=fmcaSqGoMQ&z=9bY5iRVg1AwQ&ow=0.392392&ox=0.110179&oy=0.911550&oz=0.054466&select=Sol:Earth&fov=17.670359&ts=10000.000000&rf=4&lm=-1073746936<d=0&rf=40855&lm=49152
Chase Earth:
cel://Chase/Sol:Earth/2003-06-21T12:45:17.22582?x=kMnZBfwWv5W9DA&y=j9HraGo1OQ&z=IR+L+y1myw4Q&ow=0.446316&ox=0.136645&oy=0.882509&oz=0.057518&select=Sol:Earth&fov=17.670359&ts=10000.000000&rf=4&lm=-1073746936<d=0&rf=40855&lm=49152
Lock Earth-Sol
cel://PhaseLock/Sol:Earth/Sol/2003-06-24T15:20:00.95615?x=cISqz2h3b2q+DA&y=wgQOv8QSOA&z=+SrZj06EOgsQ&ow=0.469314&ox=0.139005&oy=0.870319&oz=0.054474&select=Sol&fov=17.670359&ts=10000.000000&rf=4&lm=-1073746936<d=0&rf=40855&lm=49152

To see the difference between Chase and Lock:
Chase Halley:
cel://Chase/Sol:Halley/2003-06-29T08:31:36.45672?x=KJ5XaWkAyH6WCw&y=H2OzXQHAa+x7/////////w&z=7zPM23p7CbDL/v///////w&ow=-0.281803&ox=0.755442&oy=-0.491677&oz=-0.328859&select=Sol:Halley&fov=55.172916&ts=10000.000000&rf=4&lm=-1073746936<d=0&rf=40855&lm=49152
Lock Halley-Sol:
cel://PhaseLock/Sol:Halley/Sol/2003-06-30T08:21:58.24661?x=YsWh65oaYXuWCw&y=WOjAUhV+Q+p7/////////w&z=1O/5sz7vsqjL/v///////w&ow=-0.132292&ox=0.839690&oy=0.398379&oz=-0.344549&select=Sol&fov=55.172916&ts=10000.000000&rf=4&lm=-1073746936<d=0&rf=40855&lm=49152

Christophe:

Thanks for the cel:urls. I have also been confused about Chase and Lock. When I tried both, I frankly could not tell the difference. Both seemed to do the same thing. Could you highlight the differences in words? Thanks

Frank

Frank,

In Chase mode, your position remains fixed relative to the target's direction of motion. If you're directly in front of or behind the target (in terms of its motion), you'll remain there regardless of how it moves.

In Lock mode, your position remains fixed relative to a line between the target and a second object. As the second object moves around the target (relatively speaking) so do you. Thus if the second object is Sol, the illuminated fraction of the target (its "phase") remains the same because you're moving around the object in sync with Sol.

For the Earth and Sol the two modes give similar results because the Earth's direction of motion is always at about a right angle to the line from the Earth to Sol.

For the Moon and Sol, the modes give very different results. In the case of the Moon, Chase mode is more similar to Sync Orbit mode (although the Moon wobbles around quite a bit) because the Moon's direction of motion is nearly fixed with respect to its surface (in terms of longitude, at least). Lock mode maintains the Moon's phase, so the Moon is seen to rotate once a month.

- Hank

A good way to get a feel for the difference is to try lock and chase with a comet. Because comets generally have highly eccentric orbits, the direction of motion will not always be almost perpendicular to the direction to the Sun. In lock mode the Sun will stay fixed, but it will drift across the field of view in chase mode. Also, lock can be used with any two objects. Try selecting the Earth and locking on Mars. Select Earth, press F to follow, select Mars, and press : to lock . . .

(Oh . . . try a comet other than Halley because chase and lock currently don't work so well with rapidly precessing objects.)

--Chris