and the mysterious offset

I'm making my own ships for a project and I've encountered a problem when trying to create engine glows. My basic method for creating the 36 different frames is centering a camera over the center of rotation of the ship, then taking a screen shot of the exact same location (as shown by cursor coordinates) as I rotate the ship through 360 degrees, and finally"quilting" the resulting shots together into a rle8 resource.

My problem is that when I repeat the process, this time with engine glow (via volumetric flames) and the rest of the ship completely matte black (giving just the silhouette), when I run the ship in Nova, the flames are offset by just a few pixels below where they should be, but only the effect varies as the ship spins around, causing the flames to either detach from the ship when pointing left or right, or to ride up over the hull when pointing down. The only time where the image looks fine is pointing straight up.

I've checked to see how Nova does this seemingly easy effect, and as far as I can tell, the flame rle8 are larger than the actual ship rle8's, but the difference doesn't seem to follow any constant of proportionality between, say, the shuttle, Leviathan, and Terrapin. So, I've tried to increase the "tile size" of the 36 engine glow frames to mimic Nova's setup, but this obviously hasn't worked. If you can offer any advice, I would appreciate it greatly.

-Werhner,
a noted rocket scientist

Werhner, on Dec 8 2004, 09:50 PM, said:

I'm making my own ships for a project and I've encountered a problem when trying to create engine glows. My basic method for creating the 36 different frames is centering a camera over the center of rotation of the ship, then taking a screen shot of the exact same location (as shown by cursor coordinates) as I rotate the ship through 360 degrees, and finally"quilting" the resulting shots together into a rle8 resource.

My problem is that when I repeat the process, this time with engine glow (via volumetric flames) and the rest of the ship completely matte black (giving just the silhouette), when I run the ship in Nova, the flames are offset by just a few pixels below where they should be, but only the effect varies as the ship spins around, causing the flames to either detach from the ship when pointing left or right, or to ride up over the hull when pointing down. The only time where the image looks fine is pointing straight up.

I've checked to see how Nova does this seemingly easy effect, and as far as I can tell, the flame rle8 are larger than the actual ship rle8's, but the difference doesn't seem to follow any constant of proportionality between, say, the shuttle, Leviathan, and Terrapin. So, I've tried to increase the "tile size" of the 36 engine glow frames to mimic Nova's setup, but this obviously hasn't worked. If you can offer any advice, I would appreciate it greatly.

-Werhner,
a noted rocket scientist
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This sounds like more of a modelling problem than an engine one. First and foremost I would suspect that you are rotating the ship and glows as a single object? If so, you are elongating that object and changing its center of rotation in relation to the original ship, making it appear slightly offset. The additional length will sometimes cause the effect you mentioned

That's my best guess, as it was something I initally overlooked when I started doing ships too. If you can tell us what modelling problem you're using, I'm sure someone here can tell you a good method for how to adjust for this

This post has been edited by BariSaxGuy5 : 08 December 2004 - 10:18 PM

I believe BariSaxGuy meant "modeling program" at the end there...and yes, that would be useful information. I render out my ships and engine glows using a method very similar to yours, except that the program renders and saves the frames out instead of me taking screenshots by hand, and I model the engine glows along with the ship and just show/hide them as needed, so I know that if everything works as it should, they should line up.

I haven't had any alignment problems, so it sounds like there is some small flaw in your method of working that's been overlooked. Are you certain yours screen capture area, as well as the view from which you are capturing, is exactly the same when you capture the engine glows as when you capture the ship?

Yeah, like bsg said, it sounds like a problem with your grouping. When you group and object, the group rotates round the centre of the object (x1-x2/2, y1-y2/2, z1-z2/2). When you have that group for the ship alone, the centre of the ship will be slightly in front of the centre of the ship when the glows are grouped with it causing the anomaly you are seeing.

Now, in Strata, I got round this problem by having the ship grouped into one object and using the link tool to attach the flares to the group (link tool makes it act like its attached, but doesn't physically become part of the group - ie the centre of the ship remains the same with or without the glows attached). Now depending on what program you are using there will be different ways to address this problem.

This post has been edited by Jules : 09 December 2004 - 08:04 AM

Alright, I got it. Thanks Jules! It turns out that the only difference between the two rotations was the addition of 3 objects (the volumetric flames) that slightly changed the overall point of rotation of the group, causing the offset in the game. I redid both the ship and the engine glow as one group, just switching off between having a black ship and having a black engine glow. It works fine now.

Werhner,
a noted rocket scientist

Werhner, on Dec 9 2004, 10:48 AM, said:

Alright, I got it. Thanks Jules! It turns out that the only difference between the two rotations was the addition of 3 objects (the volumetric flames) that slightly changed the overall point of rotation of the group, causing the offset in the game. I redid both the ship and the engine glow as one group, just switching off between having a black ship and having a black engine glow. It works fine now.

Werhner,
a noted rocket scientist
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I assume you're using strata. If so, it's much easier to group the ship and the flares together from the outset, and render the base sprites by double clicking the group in the modeling window and hiding only the flares. The ship will still rotate as though the flares were there, but they will be completely omitted from the render. Do likewise for the ship when you want the flares to be shown. This will stop the blackened glows from obstructing parts of your ship when you get a bad camera angle.

Actually, I'm doing this off a windows 3d program I found called CyberMotion 3d Designer. It wasn't in that poll listed earlier, and its a bit on the simple side, but it can do everything that I have the will to learn. I actually need to purchase it so I can save ships and redo spins, but as of I right now, my methodology is a bit on the cheap side, just keeping the computer on and the program running until I have the spins, hails, and big shipyard pics done. Not pretty or easy, but I'm a miser. Also, the few ships I have tried engine glows with were all done top-down, so I haven't encountered the problem of a engine glow blocking the ship, but you definitely saved me some trouble when I move on to isometric spins. Thanks!

Werhner,
a noted rocket scientist

BariSaxGuy5, on Dec 10 2004, 03:18 AM, said:

I assume you're using strata. If so, it's much easier to group the ship and the flares together from the outset, and render the base sprites by double clicking the group in the modeling window and hiding only the flares. The ship will still rotate as though the flares were there, but they will be completely omitted from the render. Do likewise for the ship when you want the flares to be shown. This will stop the blackened glows from obstructing parts of your ship when you get a bad camera angle.
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I could kiss you. Seriously I could.

I've been looking ages for a simple way to render with and without flares, but too no avail, until now. Up until now I've been using a variety of duplicates. (one file with flares, one with out etc)

It's so bloody obvious now though, its annoying bangs head off desk

Thanks.

TheRedeemer, on Dec 11 2004, 04:30 PM, said:

I could kiss you. Seriously I could.

I've been looking ages for a simple way to render with and without flares, but too no avail, until now. Up until now I've been using a variety of duplicates. (one file with flares, one with out etc)

It's so bloody obvious now though, its annoying bangs head off desk

Thanks.
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Just remember to link the glows to the ship, not group them - otherwise, the rotation centre of the ship will be off