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Newb trouble with x y z axes

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Newb trouble with x y z axes

Postby KNSCI » Fri Apr 18, 2014 11:43 am

Sorry to be so ignorant, but...

I'm getting satisfying Fusion results with SLS-1, but in processing the scans, I'm having difficulty with the axes:
1) when I try to rotate the view, of what, looking at the screen across the keyboard, would be a vertical axis from base to top of screen, by right-click, left-right scroll, the image rolls around an axis from my chest to the screen...
2) when I have successfully saved stls in the past, and add them to a B9Creator Layout, the axes seem mixed up. When I add the stl from DAVID, it comes out rotated 90 deg in B9 Layout. When I try to rotate it as needed, the xyz seem mixed up, entering a rotation angle in x seems to move around B9's y-axis, that sort of thing. (I also see this in stls from CAD guys using Rhino or ZBrush).

So...
what are the xyz axis references in DAVID?
how to rotate a set of scans in DAVID around a 'vertical' axis, or from bottom of display to top?
how to get DAVID axes to match B9 and other CAD axes?
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Re: Newb trouble with x y z axes

Postby WalterMo » Fri Apr 18, 2014 12:24 pm

I am doing nearly the same job like you: Scanning with DAVID and using the B9C Slicer to provide my self-built DLP printer with the necessary slices.

Yes, you are right, both coordinate systems don't correspond completely. Therefore I use the free MeshLab software to turn the scanned object in the right position for Mike's layout build platform.

In MeshLab:
Import the Mesh file as OBJ or STL.
Goto Filters (top left) => Normals, Curvatures and Orientation => Transform: Rotate.
Choose for center of rotation: barycenter.
Don't rotate the object by mouse, its position isn't absolute!

Export as STL.

Fine rotation in the B9C layout window.

PS. Here you can find DAVID's coordinate system (Jul 22th):
viewtopic.php?f=10&t=4699&p=23362&hilit

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Re: Newb trouble with x y z axes

Postby KNSCI » Fri Apr 18, 2014 5:21 pm

Hi Waltermo, Many thanks for the helpful reply and link!

I see from the diagram on the link that the coordinate system is not what I expected.

Maybe it helps to know that my 'thrown into the 3d pool' experience was assembling and learning to operate the B9. We like the results quite a lot and have become resin distributors for India, where we're based. Then we added the SLS-1.

So from B9 you know that I think of xyz in terms of the build table, with the 'Top' view showing x pointing horizontally right, y vertically and z towards the user. To see the David orientation with y where I imagine z to be will take a little while to become one with.

I'm downloading MeshLab now, also have Meshmixer on the computer but am a bit overwhelmed with it. Would you suggest one or the other for a new user? either one have Help files written in a more newb friendly way as far as you know?

Will follow your instructions on MeshLab and most likely achieve success!

I'm also wondering about a lightweight CAD sw that might allow simple corrections to our fused scans. ie, in scanning objects with flat bases, and fusing with 'close holes' in order to get a solid model for B9 printing, the base produced is usually quite artful. I tried last time using the cleaning tool looking at the aligned scans from the side to make a straight cut across the bottom but Fusion still put in some awkward base. I'll move it to -z position in B9 but that's kind of clunky. That sort of minor correction we're looking for without a lot of CAD overhead.

Again, thanks for the wonderful help!
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Re: Newb trouble with x y z axes

Postby MagWeb » Fri Apr 18, 2014 5:57 pm

Think you should learn both Meshlab as well as Meshmixer.
Meshlab is great doing operations on the whole mesh.
MeshMixer gives the possibility to modify also parts of the mesh.

Rotating a mesh in MeshMixer is pretty easy:
Import your file.
Hit "T" on your keyboard (or via UI: Edit/Transform).
A 3D manipulator will appeare. Via click and drag you can move the object with the arrow handles, scale it per axis or global via the square handles or rotate it via the angle curves. If you click and drag on such a curve you can see the degrees displayed in a circle aroud the objects center of mass. Dragging the mouse over this circle rotation snaps to the next subdivision. So it's easy to snap to precise 90°.
Click Accept (or "A" via keyboard)
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Re: Newb trouble with x y z axes

Postby KNSCI » Fri Apr 18, 2014 6:41 pm

Magweb;
Thanks for the quick and helpful reply!
Please don't laugh at my ignorance on this, but the DAVID coordinate system reflects the standard in the CAD world, and the B9 is either anomalous or maybe that is the standard in printing?
Is there a way to display the axes in DAVID? it might help me learning.
Also, can I rotate the Fusion in DAVID just prior to saving it, to match the B9?
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Re: Newb trouble with x y z axes

Postby MagWeb » Fri Apr 18, 2014 10:16 pm

There are two "worlds" in 3D:

Architecture and engineering are comming from 2D floor plans. Their first plane is a horizontal one with X and Y. Adding a third dimension in 3D apps meant that the third, Z has to be the vertical one. Thus technical based apps use the "z-up" way. This is also used in machining (CNC or 3D printing).

3D modelling instead started from 2D where the first plane was the PC's monitor where the canvas is vertical (the screen). So X is horizontal and Y is vertical. Therefor the third dimension Z had to be a horizontal one.That's why modelling apps use the "y-up" way.

That's a problem of two different conventions.

DAVID uses y-up by default. For a single scan the origin is there where the calib corner's edge was at a height where two ring markers are in a horizontal row. You can toggle the origin hitting "C" in shapefusion (red: x, green y, blue Z)

BTW: In MeshMixer's import dialog is a checkbox to rotate the object from y-up to z-up (or z-up to y-up) at import AND export.
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Re: Newb trouble with x y z axes

Postby KNSCI » Sat Apr 19, 2014 10:36 am

MagWeb;
Can't say thanks enough for your clear and concise reply, now I get it! If you had to laugh, I hope it was enjoyable!

I've downloaded the MeshLab and opened it and it's going to take some time to learn but at least I can get started with it by rotating files that I'm going to use in B9, which will be helpful.

Making progress, thanks to you.
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Re: Newb trouble with x y z axes

Postby WalterMo » Sat Apr 19, 2014 12:00 pm

And if you since have a large file in MeshLab you can easily reduce its number of vertices & faces.

Goto Filters => Remeshing, Simplification and Reconstruction => Quadric Edge Collapse Decimation.

I already have printed several things, but never > 136 MB (as STL).

PS. I have just tested the mentioned tool but it only worked for one time. The next reduction-try lets the software crash. Strange. :?:

OK, so I had to save each result, open again MeshLab and do the next reduction.
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Re: Newb trouble with x y z axes

Postby MagWeb » Sat Apr 19, 2014 12:27 pm

@ KNSCI:
No reason at all to laugh. In my post above I made a mistake also. You may have noticed that describing the first architectural floor plane I also made the mistake to write "Z" instead of "Y" (corrected now).

@ Walter:
To prevent a crash in ML you've to close the filter's dialog and run the filter again if you wish to do a further reduction (at least here in the MAC version)
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Re: Newb trouble with x y z axes

Postby WalterMo » Sat Apr 19, 2014 4:42 pm

Gunter,
I had tried everything to solve the problem. But nothing worked. It's version 1.3.2 / 64Bit.

Now I have tested the same on my notebook, same version, same problem. :(

But, on my notebook is also an older version (1.3.1 / 32Bit) installed. And this version works!
And, I don't have to close the Decimation window after each run. I can simply reduce and reduce......

Is it a bug? Maybe other guys like to test this MeshLab tool with version 1.3.2 / 64Bit.

Good to know: After 1x reduction it is possible to turn the object without problems.
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Re: Newb trouble with x y z axes

Postby MagWeb » Sat Apr 19, 2014 5:55 pm

Just updated ML to 1.3.3 - now reduction seems to be stable again (without need to close the dialog which worked here)
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Re: Newb trouble with x y z axes

Postby WalterMo » Sat Apr 19, 2014 8:50 pm

Didn't know that ML version 1.3.3 is available now. Instead at SourceForge I had looked at the wrong site (heise.de).
Now with 1.3.3 all works fine. No crash and no window closing necessary.

Thanks for the hint.
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