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NavMesh

Postby Winterhawk99 » Mon Feb 20, 2012 4:40 am

I watched the Bashaba tutorial on NavMesh which was ok but left alot of questions. Such as what to do with upsidedown faces if you find them. techinques I learned like flipping a model updside down to find holes werent covered and what to do with overlapping mesh such as with bridges. I'll look for some more tutorials on the subject but if anyone has suggestions please post. So far I haven't seen anything actually explaining what you are doing with navmesh and why you need it. Those of us with NWN modeling experiance will know its similar to walkmesh but with the ability to overlap at some point along the z-axis in the case of bridges and such. For those that really dont know the ins and outs the videos still leave them clueless as to what they are actually doing.
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Re: NavMesh

Postby rdjparadis » Mon Feb 20, 2012 7:32 am

I haven't looked into it in the Creation Kit, but in the UDK a NavMesh is basically what the AI can 'see' in the game of where it could walk. Usually a NavMesh is smaller than the actual walkable space, and is unrelated to PC movement in UDK. I don't know if it's the same in Skyrim, but from my knowledge of the subject I would assume it does work pretty much the same.

Basically, if you don't have a NavMesh on an area, NPCs, animals, monsters, etc. will not walk there, but a PC may be able to.
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Re: NavMesh

Postby Bannor Bloodfist » Mon Feb 20, 2012 11:56 am

Yeah, it appears that the navmesh might coincide with "pathnodes" from NWN land. A bit more detailed, and customizable, but basically same idea. The PC/NPC can't "see" an easy way to get from point A to point B without a navmesh, but they can STILL move over those areas if the area is actually walkable. NPC's seem to be more restricted though.

I have seen locations where it would be logical for an NPC to hide for attack purposes, but he NPC doesn't appear to see the space as available. I have also seen where the NPC will walk off of what you would consider the normal path, run out of what I assume is the navmesh, stop, go backwards, and find the real navmesh to continue down the path.

This means we will have to pay attention to actual walkable vs navigable spots on any map we create.

I have also noticed a large number of objects that SHOULD be walkable and/or solid, but actually are not. Meaning someone placed a large stone surface on top of the normal tile floor, and NPC's will disappear inside the stone when they die... they are there, and sometimes you can even loot them, but you can no longer see them. This is again something we will have to pay attention to.
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Re: NavMesh

Postby Winterhawk99 » Mon Feb 20, 2012 6:02 pm

So what your saying is theres most likely another pc walkmesh of somesort tied to the tile models attached to an origin dummy?
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Re: NavMesh

Postby Bannor Bloodfist » Tue Feb 21, 2012 3:46 pm

Winterhawk99 wrote:So what your saying is theres most likely another pc walkmesh of somesort tied to the tile models attached to an origin dummy?


Yes, that is basically what I am saying, I do NOT know how it is accomplished, it may be that the engine performs some mathematical calculations or something, IE, is the height difference and/or angle too steep? I know that if I can get to the TOP of any mountain, I can go down, if I carefully choose my drop path. I can literally walk down a very steep wall of that mountain that I can NOT climb upwards on. So, the game handles that fairly well.

Think of it in reference terms only, as the actual .wok object in NWN, with the Pathnode laid on top. I am sure you have seen NPC's in NWN get "stuck" when there is perfectly clear walkable space around them? They get stuck because the engine is attempting to overlay the pathnode object on top of the actual wok. If the wok doesn't exactly match, or come very close to matching that pathnode, the NPC gets hung up on whatever object is blocking it. Some folks in NWN attempted to get around this by always using the "A" pathnode, the "+" type. But this really doesn't work all that well for complicated space.

Here in Skyrim, it appears to have the same sort of thing, some base walkable object space, with the Navmesh laid on top. I have seen objects, likely placeables, primarily rocks, that I can walk right through or objects can fall through. I have seen NPC's die, and fall through the floor that is normally walkable. Sometimes bits and pieces of them will stick upwards through that floor that the PC can walk on. So what I am assuming is happening is that the engine is using the navmesh for true walking, but falls back to walkable space after that. So, a bridge, or deck laid on top of a bunch of rock, the engine with it's overpowered death animations, can move the NPC beyond the navmesh, so the NPC defaults to the true walk space below it instead. Since it is stacked "Z" levels, it can get easily confused.

So, something is definitely different in how walkable space is created. We really need to find someone that has experimented more with the Gamebyro engine to tell us. Not even sure where or what to start searching for on that.

Anyway, don't let all of that confuse or frustrate you yet. I don't think it will end up being all that complicated, it is just something we need to look at and learn a bit about.
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Re: NavMesh

Postby rdjparadis » Wed Feb 22, 2012 7:22 am

My guess is the actual walkable space is all physics driven, which means there's no data structure you can edit for that. In the examples given where a dead creature seems to fall 'through' some rocks or some such, I bet that their death animations somehow take them beneath the top surface of the placeable somehow, so they fall until they hit another object(the real floor usually). That would probably be a bug in either the death animations, or in the engine code for handling the physics itself. The former we could deal with and fix/lookout for. The latter we may be able to work around, but can't fix. Future game patches may fix the second bug if that's what it is.
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