[Fury]

if I wanted to know a ship's weight/mass, any good ideas how to accomplish that? I am well aware that that PCS2 displays ship's mass, but I do not think it can be trusted because whoever made the particular ship could have just as well pulled the mass value out of thin air. If I were to use only retail models, I guess the mass value in pof could be used but when you throw community-made ships in the mix, it gets hairy.

I figured it'd be possible to find real values out by converting pof into dae and then load it in Blender and have it re-calculate the model's mass or weight, whichever it is. I did just that, but got totally lost once I opened Blender. I have no clue what to do with Blender or if this is even possible in Blender. Okay so of course it wouldn't be real weight or mass because the ships aren't full of solid matter inside, but it'd be close enough.

[Sushi]

What do you want the mass for?

And why do you think looking at the model is the best way to figure it out (as opposed to, say, making it up?)

[bigchunk1]

Well, can you compute the volume of a mesh using some sort of modeler?

Density = Mass/Volume  => Mass = Density*Volume

So compute a density coefficient for the Perseus or something and then

This is what I think you are tying to do and I think it's a nice idea to get some approximations.

But, and you probably thought of this already, this method assumes that all ships are made from the same materials while I think it's a fair guess that they are not. Some fighters have more cargo space for missiles while others have better thrusters, some have larger power plants etc.

I guess it's interesting to at least muse at the density of the materials used in the various ships, since it would force you to think about what actually goes into building the ships, but I think if you go that deep you're probably going to be more accurate than Volition. 

[JGZinv]

I'd think something like whatever the equivalent mass/volume of solid iron would be, less 35%.. would come close for a fighter.

For capitals you'd have to consider that decks, crew space, cargo area, etc.. would render a larger empty space.

[-Norbert-]

There would also be the matter of different materials used. Surely armor isn't just a think slab of metal slapped onto the capships in FS2. They most likely have layers of different materials, to protect from different weapons (explosion, armor piercing, heat-based weapons, ect.), something else to build the interior of the ship (using state of the art armor plates to build a corridor would be a big waste of ressources) and yet more variables for the ship's systems and the already mentioned decks and such.

You could go at it from another angle and calculate it from the ships inertia. If you have the engine power and put it into a formula with how fast the ship accelerates, you should be able to calculate the mass from it.

[Fury]

Well, can you compute the volume of a mesh using some sort of modeler?

Wasn't that the question? Maybe Blender can do it, but I have no clue how.

But, and you probably thought of this already, this method assumes that all ships are made from the same materials while I think it's a fair guess that they are not. Some fighters have more cargo space for missiles while others have better thrusters, some have larger power plants etc.

I guess it's interesting to at least muse at the density of the materials used in the various ships, since it would force you to think about what actually goes into building the ships, but I think if you go that deep you're probably going to be more accurate than Volition. 

I'd think something like whatever the equivalent mass/volume of solid iron would be, less 35%.. would come close for a fighter.

For capitals you'd have to consider that decks, crew space, cargo area, etc.. would render a larger empty space.

There would also be the matter of different materials used. Surely armor isn't just a think slab of metal slapped onto the capships in FS2. They most likely have layers of different materials, to protect from different weapons (explosion, armor piercing, heat-based weapons, ect.), something else to build the interior of the ship (using state of the art armor plates to build a corridor would be a big waste of ressources) and yet more variables for the ship's systems and the already mentioned decks and such.

You could go at it from another angle and calculate it from the ships inertia. If you have the engine power and put it into a formula with how fast the ship accelerates, you should be able to calculate the mass from it.

All of above are irrelevant for my needs. For all I care the ships can be solid lead inside. Basically all I need to take into account is the ship's volume, but since ships aren't boxes I can't just use the width, height and depth PCS2 gives.

[Droid803]

if I wanted to know a ship's weight/mass, any good ideas how to accomplish that? I am well aware that that PCS2 displays ship's mass, but I do not think it can be trusted because whoever made the particular ship could have just as well pulled the mass value out of thin air. If I were to use only retail models, I guess the mass value in pof could be used but when you throw community-made ships in the mix, it gets hairy.

I figured it'd be possible to find real values out by converting pof into dae and then load it in Blender and have it re-calculate the model's mass or weight, whichever it is. I did just that, but got totally lost once I opened Blender. I have no clue what to do with Blender or if this is even possible in Blender. Okay so of course it wouldn't be real weight or mass because the ships aren't full of solid matter inside, but it'd be close enough.

PCS2 automatically calculates the mass of a model on import, doesn't it?
I've never had to enter a value myself.

Even if there is a value already there, a clean export/re-import through DAE should reset the mass.
That, or you just clear the field altogether.

[Fury]

Even if there is a value already there, a clean export/re-import through DAE should reset the mass.
That, or you just clear the field altogether.

Simple solution. I'll see what happens later today.

[Alan Bolte]

On the question of mass, density, and what Freespace mass units actually mean, here's a fun exercise:
ast01.POF has a max radius of 65.831612. It's very roughly spherical, so to compute its actual volume you'd probably want to use a radius 80-90% of that to compute the volume. To calc an upper limit though, let's just go with the max. IIRC FS distance units are meters, so multiply by 2 to get the diameter, and plug that into this Asteroid calculator.

Depending on the composition of the asteroid, we can see that at most its mass would be 9.4 million metric tons. We haven't calculated a lower limit, but 1 million seems reasonable.

ast01.POF has a mass of 25865.355469 FS units. From this we can make an order of magnitude estimate that if FS units have any internal consistency at all, a FS mass unit is equal to 100 metric tons.

An Aeolus has a mass in FS units of 27234.916016, so let's call that 2.7 million metric tons. Compare that to the similarly-sized Essex-class aircraft carriers of WWII, which had a displacement of no more than 37 thousand metric tons.

That's a fairly big difference, but on the other hand an Aeolus doesn't get vaporized when a fusion warhead detonates on contact with its hull.

This does, however, mean that a Herc 1 weighs as much as a WWII fleet carrier.

[Killer Whale]

This does, however, mean that a Herc 1 weighs as much as a WWII fleet carrier.

I don't find that too unreasonable actually, its a heavy assault craft taking heavy damage from heavy weaponry, it needs some heavy armour to survive. What I would find unreasonable would it being only a few dozen tonnes.

[Black Wolf]

I think we can pretty safely ignore the pof values for mass. They're there to tell the game how each object should behave - that doesn't neccesarily have any connection to an actual, realistic mass value.

[Woolie Wool]

This does, however, mean that a Herc 1 weighs as much as a WWII fleet carrier.

I don't find that too unreasonable actually, its a heavy assault craft taking heavy damage from heavy weaponry, it needs some heavy armour to survive. What I would find unreasonable would it being only a few dozen tonnes.

A WWII fleet carrier is over 10,000 tonnes. The Germans came up with enormous tank designs that were larger than an Ursa, and could barely move, that still only approached 1,000 (remember that these were tanks, not aircraft or spacecraft, and could not exceed a walking pace). I'd say the maximum a Herc could possibly weigh is 300 tonnes. And honestly I'd say it's closer to 30-40.

Remember that mass is the enemy of performance. For a fighter you want as little mass as possible. There's also the issue that if most of the volume of the Hercules is armor, where do you put the internals--guns, missiles, powerplants, electronics, life support, shield generators, etc?

[Droid803]

...Tanks have to be able to support their own weight in gravity, and have to be able to move over land and not sink into the ground, and has to content with surface friction.

In space, there is no friction, so any little push and it'll start moving. And stuff doesn't have to support its own weight either.

So if anything, stuff can be heavier in space and still be fine. Sure, you'd have to say **** all to your delta-v, but hey, once it starts moving, it'll keep moving. Stopping it is an entire other matter. It is true that for any combat spacecraft, though, that you would want as much delta-v as possible. But since when has FreeSpace been remotely hard sci-fi? Hell. these things have a top speed in space.

[headdie]

...Tanks have to be able to support their own weight in gravity, and have to be able to move over land and not sink into the ground, and has to content with surface friction.

In space, there is no friction, so any little push and it'll start moving. And stuff doesn't have to support its own weight either.

So if anything, stuff can be heavier in space and still be fine. Sure, you'd have to say **** all to your delta-v, but hey, once it starts moving, it'll keep moving. Stopping it is an entire other matter. It is true that for any combat spacecraft, though, that you would want as much delta-v as possible. But since when has FreeSpace been remotely hard sci-fi? Hell. these things have a top speed in space.

not to mention C

[Fury]

Even if there is a value already there, a clean export/re-import through DAE should reset the mass.
That, or you just clear the field altogether.

Simple solution. I'll see what happens later today.

So I tried this method just now and unfortunately it doesn't work. When I open a pof into PCS2 and clean out the mass field, it simply resets to 0 and stays as such even if converted to dae and back to pof. Even if I don't clear out the mass value prior to conversion, it just keeps using the old value.

So I don't see how I can force PCS2 to re-calculate the value.

[Fury]

The E kindly provided me with details how PCS2 is supposed to calculate mass in the first place.

Code: [Select]

model->SetMass((model->GetMaxBounding().x - model->GetMinBounding().x) * (model->GetMaxBounding().y - model->GetMinBounding().y) * (model->GetMaxBounding().z - model->GetMinBounding().z));Makes me want to headdesk so hard. As you probably already figured out, shape of the ship doesn't really matter when calculating mass. A ship could basically be like a donut and PCS2 would give it same mass as if it was like a rock.

So much for the spreadsheet magic I wanted to use.

[karajorma]

Sounds like you need a bathtub, water and a naked Greek man.

[Droid803]

Except that finds volume.
Not mass.

Well, unless you assume uniform density...which I suppose is what we're doing.

I do believe that there are algorithms that do something like that, but won't work on some models because sometimes they aren't one closed object (err, non-manifold).
Actually I think that if its non-manifold there's actually no way to actually find its...volume, cause its just a bunch of sheets, really (which may or may not form a closed volume)

[Fury]

Volume would work just as fine assuming someone comes up with relatively accurate means to calculate it for all ships. Otherwise it does seem I'm stuck with using bounding box which won't be all that accurate.

[BengalTiger]

Aren't the 3D models simplified into boxes for collision detection?