Are megaprims bigger than they seem??

I rezzed a megaprim and according to the mini-map, is was totally contained on my land. Then I stood it on its edge and the mini-map now shows overlap on the neighbours land.

Is the mini-map the problem or does a megaprim have an invisible part to it?

I tested with a 256x256x1 prim, it was definitely the same size as the region, but its square on the mini map was much larger. It's not just megaprims, though... (snapshot http://flickr.com/photos/day-oh/1907901442/ )

The mini-map can be inaccurate in this regard. However, there is also the issue that some megaprims have been modified to look smaller than they are. Look at the true dimensions in your edit window.

It's well documented that the "footprint" and the center-of-mass for mega-prims is not as you see them. Wether this was intended in order to create them, or is a by-product of their effect on the grid would have to be defined by a core programmer.

However, the fact that their center of mass and footprint are not where the visible representation of the prim is at, is one of the reasons some people do not like them. This may also be the reason that LL is having trouble with some of them in the Havok4 environment.

I expect LL will eventually remove them rather than deal with the ramifications of their impact on physics within SL. They could keep those that work, but given LL's past record....you make the call.

Build with them at your descression, but keep in mind that they can be reported, not only for lag, but for encrouchment over boundry lines. Yes, even just the footprint going over the lines if the other parcel owner can show inherent problems from it. Usually in the form of camera interference.

If on good standing with yoru neighbor, just let them know about it, and offer to (re)move it if it causes problems. 99% of the time, neighbors will work with you if they know thngs are there. It's when they don't know what's going on that they file reports and such.

~Jessy

I have noticed that if you have a mega prim that has PATH CUT, the prim can alter your view as well, as the system somehow sees the prim in full even if its path cut to its smallest form. This would be the same with the mini-map I think.

some of them have been made by halving a larger prim but altho you only see one half, the center point stays the same as the bigger one.

eg a 25 is a 50 halved but it still shows up on the minimap as a 50

The minimmap can be inaccurate.. however, many megaprims are made by using dimpling and cutting and prim torture on much larger prims, so the blue square might be much larger because its counting what isnt there anymore..

However, In any case I'd recomend not using megaprims at all unless you have to, and no more than the 32m ones really.. they are the safest, but even they can cause problems. There are alot of counts towards using them fine, but yesterday I took the time to go to an empty sim (With permission from the owner) and rez various megaprims and various combinations of megas... almost every one of the had some sort of problem. The most common was when I tried to hollow it just didnt act as if it was hollow even if it showed the hollow, followed by the 'floating' effect.

Only thing I use them for is building "ground" in the sky. But yes the mini map shows overlap all the time regardless whether they are megas or just normal prims. It looks like one neighbor has completely encroached my land a good 50 meters or so but ... they actually haven't I flew up and down the border several times and they're behind their line.

Yeah I tried to hollow one for a 3 prim skybox, it looked empty but was still whole when I flew into it.

I dont suppose anyones documented the problems with each size? Seems to be the general opinion that the flat 20x20s are alright, and I use the 32x32s, they seem ok.

Yeah, I think "hollow" is pretty much b0rked in all megaprims that I've tried--but that's not unique to megaprims: until very recently, a hollow skewed cut Tube would also have a collision envelope that ignored the hollowness. (I never saw this fixed in a release note, but I couldn't replicate it on the main grid just now, so maybe a miracle has occurred.)

But I really try to avoid non-phantom megaprims. Their vast potential collision envelope makes Havoc have to think awfully hard--and we know it doesn't think very *well*, at least on the main grid. (Old saw: "If you don't think too good, don't think too much."

There are other oddities of megaprims shared by exotic regular prims, associated with difficulty in computing collision envelope. For example, try rezzing from inventory directly on top of a megaprim; one gets much the same problem when trying to rez something inside a hollow cube, or on top of a flattened cube that's been fully top-sheared in some dimension. It seems that the rezzing process just gives up when it's a bit difficult to calculate the point where the object should be rezzed.

There's a huge discussion about this going on in the Feedback forum here:
/13/b7/216541/1.html

Basically; LL want to get rid of mega-prims, but people want larger prims.
The problem with mega-prims being kept is that they don't play nice with the physics engine, and introduce problems for a large number of potential improvements or new features.
The problem with removing them is that a number of builds have used them to include large spheres, cylinders etc. that would otherwise require hundreds or thousands of prims to reproduce, and wouldn't look as good.

What we need therefore is a way to produce larger shapes but using smaller prims so we can have the best of both. I've got a proposal for this on the JIRA:
http://jira.secondlife.com/browse/VWR-2859
Please be sure to read the sub-task for this:
http://jira.secondlife.com/browse/VWR-2860

Basically that suggestion is along the lines of:
Give us primitives that can represent a chunk of a larger prim (e.g the top 10m x 10m x 10m slice of 50m x 50m x 50m sphere) which can then be put together to form the larger prim.
Give us an editor that lets us create these automatically as though we were building a larger prim. ie - it produces a larger-prim then sub-divides it into these special new primitives.
Replace all mega-prims with these new "sub-divided" prims.

Please vote for it as it would seek to remove the issues with mega-prims, while letting us build bigger shapes easily and paving the way for future improvements.

I don't know if anyone has but I'm going to see if they'll let me do my tests again, and I'll document every problem I find that I can connect to the megaprims.

Last time, I think I crashed the sim, but I'm not sure if it was me or just SL doing restarts or something again as it was time for me to go anyway...

But I'll be documenting all problems I can find with them iff the sim owner (Or any other sim owner that might read this) would let me

Hmmm... somehow I think it'll be pretty difficult to cons up my cel-shaded mega-sphere dome from smaller prims. Well, if it goes, it goes... was fun while it lasted. To be honest, though, I'd rather just lose the Havoc 4 upgrade and keep the megaprims; none of the other Havoc 4 changes seem all that important anymore, except maybe stability--if it's realized.

sculpties

In the building forum theres someone who was/is working on a 20m sphere using sculpties they did the math to make... it looks wonderful in my opinion... and can go larger with more math.

In my mind, another way using a 3d modelling program would be to just make a sphere and cut it into so many parts (Depending on the size of sphere you want in the end) and then exporting each piece as a sculpty... I don't know how well this would work, if at all...

But using normal prims (Non sculpty) making an actual sphere of more than 10m would be impossible I think..could get close with tons of work, but not a sphere... ellipse or billion sided polygon...