vc symmetry

[noob24]

i deliberately highlighted both objects just to show they both had new shaped bounding boxes thats all

 

[noob24]

ive noticed that if you use the mirror tool from the main menu 3dsmax it works perfectly and also the bounding box of the object remains 100% intact and does not become distorted(orientated to world coordinates) so my question is would it not be easier to just use this tool and then flip the normals back to avoid the normals issue in fsx that is related to using this tool? it just seems alot less hassle than the mirror modifier with its bounding box issues

i am assuming that its only the normals problem with the mirror tool that is the reason not to use it?

 

[hairyspin]

Oh just hit J and turn the bounding box off!

 

[n4gix]

would it not be easier to just use this tool and then flip the normals back to avoid the normals issue in fsx that is related to using this tool? it just seems alot less hassle than the mirror modifier with its bounding box issues

i am assuming that its only the normals problem with the mirror tool that is the reason not to use it?

No, it would not. The problem isn't just that the normals are reversed, they are inverted! The sum of the normal vectors must always be +1.

Toolbar Mirrored and flipped normals have a vector sum of -1, which looks really, really strange in the sim.

THAT is why it's a very Bad Idea.

Now, that said it is possible to "fix" this issue, but quite frankly it's far, far faster to simply do it the proper way to begin with.

 

[hairyspin]

...am i barking up the wrong tree here with this whole bounding box thing ? or have i missed a trick here...

I think you are barking up the wrong one. By concentrating on the bounding box, you're missing the point of the Pivot and how transforms affect the object.

You show a box which was rotated off the major axes after creation. When you rotated the box the Pivot followed suit, so it's also aligned off the major axes. So far, any scaling - as long as you use Local Reference Coordinate System (Local RCS) - will not distort the box off-square.

When you apply a Reset Xform operation, all transforms (move, scale or rotate) to the box as originally created are gathered into an Xform modifier which is placed on top of the stack. All scaling is reset to 100% and the Pivot is aligned to the World RCS. This operation is irreversible and we generally collapse the stack after doing this - well I do...

The bounding box is recalculated with reference to the new Pivot alignment, so it no longer closely follows the box's compact shape - instead the object determines the diagonal sizes of the bounding box.

Here's the important bit! The box is still rotated off the major axes, but the Pivot is no longer aligned with the box, so unless you've taken some other measures beforehand any scaling is going to distort the box off-square, as your screenshot shows.




And as far as the Mirror button goes; unless you want the mirrored bits to appear inside-out in the sim, do as Bill says. Better a little faffing with the mirror modifier early than heartbreak later on.

 

[noob24]

ok thanks Bill for that explaination.

i am however puzzled by this whole mirror modifier bounding box thing because it seems only i am having problems with it as no one else mentioned it at all anywhere. and all of the methods for mirroring in this thread simply dont seem to work for me unless i use the reset xform method which then seems to open its own can of worms by affecting the bounding box of an object which is undesirable as it messes up scaling and moving as it messes up the pivot orientation of an object. the pivot does not care what shape the object is, to align its self it relys on the bounding box (edit : when you align pivot to object)


so either i am making a fundamental mistake when i try it or people just arnt mentioning the bounding box problems or all the details of the procedures.

the result is im confused still. i really need someone to go through the mirror process in idiot terms exactly and clearly step by step and with out assuming any steps are a given. i think this is the onle way.

i would greatly appreciate anyone going through this for me in this way cos i cant move on and its such an important part of modelling aircraft!

i have also included a 3dsmax file here with a simple box rotated to angle that does not lend its self well to mirroring with the mirror modifier in world coordinates. the box has its bounding box intact as created and inline with its geometery.

can someone kindly take the time to open it in max mirror/ clone it in world space on the y coordinate oppersite side of grid and highlight it so its bounding box and its move transform is visable exactly as in this image and post a screen shot of that. and use the mirror modifier to mirror it.

thanks in advance

 

[hairyspin]

...the pivot does not care what shape the object is, to align its self it relys on the bounding box...

No, if that were the case the bounding box would follow the Pivot as the Pivot is realigned by the modeller. But I think we posted almost simultaneously, see my post above.

I can't give you screenshots from Max just yet, you're using version 9? and my version 7 won't open your file. If nobody else pitches in meantime I know a man who can, but you'll need to wait, sorry!

 

[noob24]

ok thanks

sorry i should have explained i little clearer what i meant.

yes i see what you mean about the bounding box following the pivot which of course it does not. what i meant was if you reset the pivot via the heirachy panel and align to object it has to have some reference in order to know what to align too. and its the bounding box that it depends on to do this not the geometary. the pivot does not care what shape the geometary is rather the shape and orientation of the bounding box. and after a xform reset the bounding box of the box in my screen shot would be aligned to world coords and no longer look the same see screen shot attached. so now this object will be a nightmare to scale because its pivot will no longer aline with its own geometary cuasing problems with scaling

 

[noob24]

ok shot one shows the object with pivot aligned to world 0.0 y axis and mirror modifier applied and immidiatly its clear the mirror center gizmo is not aligned along the world x axis as the objects transform gizmo is so you know it wont mirror how you want it. shot 2 then confirms as the object is cloned and ends up in the wrong place.

its clear to see that the mirror center gizmo is aliged to the bounding box of the object and as long as its aligned to the natural bounding box if the object is at an angle to world coordinates it will always mirror offline. (only if the object happens to be perfectly inline with world on one or other of its axis will this issue not occur as the morror will automatically line up with world on that same axis

ok so the bounding box needs to be aligned to world so apply x form reset and mirror problem sorted right? .........no
the bounding box is now no longer fitting the shape of the box. shot 3 ( both objects now with aligned to world coords bounding boxes)

but as soon as the objects bounding box is aligned to world coords . but now the objects pivot will no longer align to to shape of the object if you try to "align to object" rather it will try to align to the bounding box and that means problems for scaling and moving accurately, see shot 4 where the scale gizmo is now aligned to the bounding box even though i have manually tried to rotate the gizmo inline with the object . ok yes you can try to return the bounding box back manually as it was origionally trying to align the object by eye to world coords and then performing another x form reset but this is innacurate and guess work at best and will never be 100 percent.

so now your objects is mirrored and in its place but in effect ruined as you can no longer manipulate its scale etc etc accurately




so ok make the miirror center gizmo align with world problem solved....................no because as shot 1 shows the world rotate type in already shows 0.0 in all 3 axis so setting them all to 0 has no effect. so next option do it by hand not good or accurate infact you may as well just clone the object and place it by hand and forget mirroring it alltogether as the whole point of the mirror is to accurately place / rotate/ align an object on the oppersite side if what ever dimension/ coordinate system you choose.

 

[n4gix]

"noob," all I can tell you is that in the nearly fifteen years I've been working with both Max and GMax, I have never - NOT ONCE - even thought about the "bounding box."

Read this post I made July 5, 2007 about
"Mirroring Perfectly in Max/GMax" (click here to download PDF version)

...or read in this forum:
http://www.aerodynamika.com/cgi-bin/yabb2/YaBB.pl?num=1183676822/0#0

Note carefully that there not one single mention of "bounding box" anywhere. It's simple, it works 100% of the time.

 

[noob24]

ok then that suggests im not doing it right(mirroring process that is)

so back to the drawing board


but the fact remains aside from mirroring that if you do a reset x form and your object is not in line with world coords at the time then the objects bounding box will be altered and you will have problems with scaling as a result. this i have tested and my screen shots confirm that .( unless of course im doing that wrong too )


and i have encounterd a messed up bounding box every time i reset x form so for me its already causeing problems because my object is now impossible to scale correctly which is why all this is an issue for me weather its something im doing or not i need to get to the bottom of




Reset XForm Utility



Command entry: Utilities panel Utilities rollout Reset XForm button
Use the Reset XForm (Transform) utility to push object rotation and scaling values onto the modifier stack and align object pivot points and bounding boxes with the World coordinate system. Reset XForm removes all Rotation and Scale values from selected objects and places those transforms in an XForm modifier.

To reset the transform of a group, use the Transform button in the Reset group box of the Hierarchy Pivot command panel

 

[hairyspin]

Okay, here goes. And thanks to the man with Max 9 for getting these screenshots!

I've altered your object slightly so there's no mistaking which way round the results are - moved some vertices closer together and others further apart. All screenshots are from the same viewpoint as your original file using Perspective view, although I normally prefer the User view for this.

I've also shown the bounding boxes: I expect this is the last time I'll look at them for the next several years...

Now apply the Mirror modifier to the clone:-

Now be sure to use the World Reference Coordinate System when moving and rotating the cloned, mirrored object:-

No hocus-pocus, no fancy tricks. It just works. Here's the Max 9 file as well with the finished result:-

 

[noob24]

thankyou Tom and the man with max 9 for helping me out here. i see now that i have been adjusting the rotation and move transform type in for the mirror gizmo rather than the objects gizmo and this has been the cause of the problem. i dont know why i did that but i could not see my mistake so this is just what i needed as its very clear thank you all again

Oh and now i will not need to think about bounding boxes again either im pleased to say!!!! as that side effect of my incorrect method has now been eliminated!

 

[noob24]

i am having an issue with rotation where after i have mirrored the object i change the pos or neg sign but the figure is automatically changing very slightly a few fractions of a percent a have increased the decimal places to view this as at first glance positioning is almost correct. even if i copy and past the origional figure is still changes slightly resulting in the object being slightly skew compared to its origional.

anyone know why this is happening?

it does not happen with move tranform just rotate