Hard Light Productions Forums
General FreeSpace => FreeSpace Discussion => Topic started by: Fury on November 05, 2011, 08:42:58 am
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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.
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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?)
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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. :nervous:
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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.
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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.
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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. :nervous:
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.
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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.
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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.
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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 (http://www.stardestroyer.net/Empire/Science/Asteroids.html).
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.
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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.
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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.
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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?
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...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.
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...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
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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.
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The E kindly provided me with details how PCS2 is supposed to calculate mass in the first place.
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. :(
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Sounds like you need a bathtub, water and a naked Greek man. :p
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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) :P
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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.
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Aren't the 3D models simplified into boxes for collision detection?
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Why do you want to find out how heavy certain ships are?
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To see if they'll float.
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Well I did run into the problem of a Tiigran-Merrist heavy bomber bumping into a cruiser at full speed during a test shootout mission and giving it a velocity of some 3 m/s, so if this automatic mass calculating system would work the first time every time, it would help out a lot.
Also- I don't want my T-M bombers to sink. :p
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Why do you want to find out how heavy certain ships are?
If I know a ships (relative!) weight, mass or volume I can use that as a basis to calculate damp, rotdamp, max velocity, rotation time, acceleration, explosion radius, explosion damage, explosion blast, primary and secondary capacities, power output which in turn affects shield strength and shields and weapons regen, hitpoints, scan time and score. Probably more too and each of those can be used to calculate other values.
Then you can add modifiers wherever you see fit, for example to distinguish Fenris, Leviathan and Cain and Lilith from each other. Or tech level modifiers to make FS2-era ships better from FS1 era ships.
Bounding box volume allows me to do all that, with one caveat. A ship may be of a shape where bounding box size does not reflect the ship's actual volume, or even close enough. One such example would be the Seraphim. Eyeballing a modifier into the volume calculation would be stupid, because other ships have similar issues in different scale, such as Fenris/Leviathan (radar dome and missile turret).
So unless some bright coder can add somewhat accurate volume calculation into PCS2, the bounding box volume seems be the only option here. Unless somebody knows how to use Blender to calculate model's volume, mass or weight. I tried to comb Blender's confusing UI to find whether it could do just that, but I didn't find such option. Googling didn't reveal anything either, oddly enough. Which seems to indicate such feature does not exist in Blender.
I already have a spreadsheet including all FS1 ships where I've used bounding box volume as a base to calculate all other ship stats. It does provide very nice variety for even fighter sized ships.
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Why do you want to find out how heavy certain ships are?
If I know a ships (relative!) weight, mass or volume I can use that as a basis to calculate damp, rotdamp, max velocity, rotation time, acceleration, explosion radius, explosion damage, explosion blast, primary and secondary capacities, power output which in turn affects shield strength and shields and weapons regen, hitpoints, scan time and score. Probably more too and each of those can be used to calculate other values.
Then you can add modifiers wherever you see fit, for example to distinguish Fenris, Leviathan and Cain and Lilith from each other. Or tech level modifiers to make FS2-era ships better from FS1 era ships.
Bounding box volume allows me to do all that, with one caveat. A ship may be of a shape where bounding box size does not reflect the ship's actual volume, or even close enough. One such example would be the Seraphim. Eyeballing a modifier into the volume calculation would be stupid, because other ships have similar issues in different scale, such as Fenris/Leviathan (radar dome and missile turret).
So unless some bright coder can add somewhat accurate volume calculation into PCS2, the bounding box volume seems be the only option here. Unless somebody knows how to use Blender to calculate model's volume, mass or weight. I tried to comb Blender's confusing UI to find whether it could do just that, but I didn't find such option. Googling didn't reveal anything either, oddly enough. Which seems to indicate such feature does not exist in Blender.
I already have a spreadsheet including all FS1 ships where I've used bounding box volume as a base to calculate all other ship stats. It does provide very nice variety for even fighter sized ships.
I suppose using PCS2 or import the models into a 3d program, if you are using pcs2 perhaps use screen grabs to fix the positions and mark as appropriate, you could sub divide the ship into easier to manage volumes and measure it manually that way
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Not an easy task for one very simple reason: even if one were to find the volume of each ship, there's no indication of how solidly packed in the materials are, only some indication of what the materials are, and so on.
I think it's safe to assume that per unit of volume, FS2 ships are vastly heavier than steel water going ships given the propensity for using depleted uranium on the Iceni and Ares, for example. The Deimos's "collapsed core molybdenum" could be lighter than Titanium or as dense as a neutron star for all we know, but I'd guess closer to the latter.
Blue Planet puts the mass figure for the combined weight of Serkr team at 1,000,000 tons (it was informal in universe, so it isn't really even 'canon' within the BP context); a figure I actually think is pretty light. Your average coal train weighs in at about 10,000 tons.
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Like I have already said earlier in this topic, those points are irrelevant to me as far as this topic goes.
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Brief Google search yielded this: http://blenderartists.org/forum/showthread.php?84827-Calculating-the-volume-of-a-model/page3 which at least claims to compute volumes.
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Nice find Wanderer. So a python script for Blender, huh. I probably should try this one day even though it seems a tad complicated. Thanks.
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I know the weight of the ships
zero everything in space is weightless ;)
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Wrong. Ships in space are subject to a huge number of gravitational forces. We wouldn't have orbits and such otherwise. Lrn2physics.
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I know the weight of the ships
zero everything in space is weightless ;)
Weightless does not mean massless. lrn2physics.
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thats why i said "i know the weight" and not "i know the mass" ;)
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Doesn't matter.
http://www.physicsclassroom.com/class/circles/u6l4d.cfm
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that link doesnt say weight and mass are the same, so it does matter
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You are not "weightless" in space. Anywhere the acceleration due to gravity is nonzero, you have weight (relativity notwithstanding).
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Anywhere the acceleration due to gravity is nonzero
Which is practically nowhere statistically speaking :D
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To see if they'll float.
There is another highly scientific program which is commonly observed in the public domain for this purpose as well:
http://www.youtube.com/watch?v=zm-AkvwPdZ4&feature=related
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Anywhere the acceleration due to gravity is nonzero
Which is practically nowhere statistically speaking :D
So there you go, following on from that, there is pratically nowhere in space where you don't have weight.
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that link doesnt say weight and mass are the same, so it does matter
You have forgotten that GTVA ships have artificial gravity, and hence weight.
Whoops!
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Maybe they don't have artificial gravity, maybe they're just that heavy :shaking:
(j/k)
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Anywhere the acceleration due to gravity is nonzero
Which is practically nowhere statistically speaking :D
So there you go, following on from that, there is pratically nowhere in space where you don't have weight.
There is no point in space where an object will have zero weight, as gravity can act at an infinite distance. The force of gravitational attraction may be hilariously minuscule, but it will never be zero. But I'm sure you already knew that.
On-topic, I actually wouldn't mind having reasonable values for the mass/weight of the various ships, since I'd want to see/devise some actual specifications, and mass would be a big one.
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Aren't the 3D models simplified into boxes for collision detection?
To answer your question, because I didn't see anyone else do it; in Freespace 2, no, they're not, it's all calculated off the vertex normals. That's why it's so important to weld all your verts; too many and the game freaks out.
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I was wondering how that worked. Is that... efficient at all? My understanding is that most games' collision detection requires the artist to create separate collision models which must be composed of convex hulls.
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How does a vertex have a normal? A vertex is merely a point in space which defines one of two points which make a model's edge. Rather, do you mean that FS uses the normals from a surface/face of the model's geometry to calculate hit impacts?
OR do you mean to say that FS isolates adjacent groups of vertices and computes a normal from those groups... Yes, that must be it.
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To bring an end to this confusion:
Yes, FSO does not use simplified collision models.
No, that is not in and of itself a performance risk, because we are using something called BSP trees to subdivide the geometry. This means that, when a collision check is performed, the engine uses a succession of abstractions starting from the models' bounding box, to a subobject's bounding box within that, to a specific polygon's bounding box until it gets to the specific polygon.
Now, this tactic has worked perfectly well for retail-era models, it's only recently that it has shown its age, given the level of detail present in modern models. It is possible to do collision models (seriously, the framework is already there in the models, and in particular the $nocollide_this_only submodel property), but it's not something that is in wide use, or really tested that much.
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How does a vertex have a normal? A vertex is merely a point in space which defines one of two points which make a model's edge. Rather, do you mean that FS uses the normals from a surface/face of the model's geometry to calculate hit impacts?
OR do you mean to say that FS isolates adjacent groups of vertices and computes a normal from those groups... Yes, that must be it.
No, you probably won't hear about them in geometry class, but they do exist in the 3D graphics world, have been around for a while, and are quite useful.
http://en.wikipedia.org/wiki/Vertex_normal
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There is no point in space where an object will have zero weight, as gravity can act at an infinite distance. The force of gravitational attraction may be hilariously minuscule, but it will never be zero. But I'm sure you already knew that.
Well there may be a point where they all balance out to 0.
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There is no point in space where an object will have zero weight, as gravity can act at an infinite distance. The force of gravitational attraction may be hilariously minuscule, but it will never be zero. But I'm sure you already knew that.
Well there may be a point where they all balance out to 0.
Ok, yeah. Didn't consider that. Such a force balance would be the most tenuous of tenuous systems, though. Any shifting of any of the objects involved in that system would result in nonzero sigma-F.
I don't mean to be argumentative; I'm pretty certain we both know what we're talking about, I just want to state the technicalities. Shall we let this drop?
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Actually, can't it be zero?.... If plank length didn't exist I would agree with you, but if plank length exists, and gravitation is a distortion of space time, there should be a point where the change caused by the distortion is less than plank length. Wouldn't that cause the distortion to cease?
EDIT: I'm just intrigued by the possibility you brought up. I don't actually know what anybody is arguing for.
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So plank length is the smallest possible distance the computer running our universe is able to calculate with it's current precision?
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So plank length is the smallest possible distance the computer running our universe is able to calculate with it's current precision?
No, plank length is 14 feet, at least for the one-by-twelves we've got out in the garage. Planck length (http://en.wikipedia.org/wiki/Planck_length), on the other hand, is what you said.