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@@ -160,10 +160,28 @@ Does the object end up in an unexpected location, or at an unexpected angle? If
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. 3-D transformations are non-commutative! This means it often makes a huge difference whether you first move a node and then rotate it around an axis, or first rotate the node around an axis and then move it. Make sure you code does what you mean to do.
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. Are you intending to rotate around the object's origin along an axis, or around another pivot point outside the object? If you are trying to _rotate an object around a pivot point_, you have to create an (invisible) pivot node first, and attach the object to it. Then apply the rotation to the _parental pivot node_, not to the child object itself!
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. Did you enter the angle in degrees (0 - 360°) or radians (0 - 2*PI)? A 3D engine expects radians, so make sure to convert your values! Formula: `g° = FastMath.PI * g / 180`
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+. Did you modify one of the pre-made constants like this?
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++
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+--
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+[source, java]
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+----
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+//Never do things like this!!!
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+Quaternion.IDENTITY.fromAngleAxis(-FastMath.HALF_PI, Vector3f.UNIT_X);
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+----
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+
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+This is looks normal enough, afterall, this is a Constant right? Sorta, what you are really doing is setting a value to the static final constant `Quaternion.IDENTITY`.
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+To quote one of the core team members,
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+****
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+.Do not modify the “constants”. You will have a shit-ton of really messed up errors.
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+[quote, pspeed, Core Team Member]
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+You gain NOTHING by doing this, either. Just use new Quaternion().fromAngles() like a sane person.
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+****
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+For a deeper explaination, see this forum thread: link:https://hub.jmonkeyengine.org/t/quaternion-bug/39060[Quaternion bug?]
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+--
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-== Tip: Transformation Matrix
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+== Tip: Matrix
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This here is just about rotation, but there are three types of 3-D transformation: rotate, scale, and translate.
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mitm