Help from the experts

[Tomuk]

Hello All,

I’m struggling to achieve an effect.

I’m looking to have a moon orbit a planet on the horizontal plain, I have managed to get the moon orbit around and behind (with the help of The Dom) but it’s not quite what I’m after.

I have produced an image that demonstrates the effect, please have a look and post any suggestions.

Tom.

[Lin Evans]

That's a very easy effect to create unless you want to add slight rotation of the moon on its axis to simulate keeping the same side toward the Earth. If you are doing it with close-ups then you perhaps need to take this into consideration, but otherwise you have a pretty easy job of simply changing the size of the moon as it goes away and as it comes toward you.

Give me a few moments and I'll try to make this effect for you to see.

Lin

Hello All,

I'm struggling to achieve an effect.

I'm looking to have a moon orbit a planet on the horizontal plain, I have managed to get the moon orbit around and behind (with the help of The Dom) but it's not quite what I'm after.

I have produced an image that demonstrates the effect, please have a look and post any suggestions.

Tom.

[Tomuk]

Thank you Lin,

This is what I have produced so far..,..

Moon_Orbit_Feb25_2007_19_06_34.zip

[JPD]

I made for you an example on how to make a moon orbit on this post

It seems you didn't see it

[Lin Evans]

The issue is that you can't have the Earth rotate on it's horizontal axis as you would see it from the equator without multiple frames or a movie clip. You can easily rotate the Earth as seen from the poles, but having the moon circle the Earth as seen from an equatorial view won't work because you need multiple views of the earth as you would see from space.

What I've done is rotate the moon around the Earth in a more or less horizontal path with the earth moon always facing in the same direction. The first way is a very easy way with the moon beginning at a point and ending up at the same position. As it moves across the Earth it increases in size as if it were coming closer to you. It pauses at the point where it reaches the apparent apex of its arc then continues behind the Earth getting smaller until it dissapears behind Earth and eventually reappears, etc.

This is an "easy" but not too "realistic" simulation.

http://www.lin-evans.net/pte/earthmoon1.zip

The second way uses JPD's elipse with two rectangles and is much more complicated. Two issues must be resolved. First the orbit itself which must either be done by tiral and error or by math. I did a quick and dirty trial and error to get a more or less horizontal view. The second issue is the need to have the moon pass behind the Earth as well as between the viewer and the Earth. To do this I used two Earth png files. One is at zero opacity at all times the moon passes between the viewer and the Earth then at 100% opacity to hide the moon as it passes behind the Earth. The third issue is that when treated as a child of the second rectangle the Moon will want to rotate so there are frequent "corrections" requiring keypoints to keep it from its normal rotation and preserve the appearance. This is a much more "realstic" appearing simulation but also much more difficult to do right. I didn't really "do it right" but you can get the idea.

http://www.lin-evans.net/pte/earthmoon2.zip

Best regards,

Lin

Thank you Lin,

This is what I have produced so far..,..

[Tomuk]

My thanks to Lin , JPD,The Dom and all who helped find the answer.

I have the effect I need thanks to you all.

Tom.