Some confusing with Slice Geometry

bonej

#1

Hi, Michael!
First, thank you again for the BoneJ and its upgrading. Well, I continue my research on tibias, and here’s the issue. I take a middle slice from each bone, oriented in sagittal plane (the top of image is cranial direction, the bottom is caudal). Then I want to calculate the moment of inertia in this cranio-caudal direction, but I need the center to be neither the center of image (as it initially draws) nor the centroid (which we can get from Moments of Inertia by analyzing the whole bone), but the center of masses (center of balanse), calculated from this particular slice. So how can I do that?)
Thanx in advance!
With all respect, Mitya


#2

Good question

Please don’t be distracted by the centre of the Orientation cross-hairs. Remember, an orientation has a direction but no location: it is just a unit vector (or more correctly an eigenvector). Another way to represent it visually would be to have lots of little crosshairs spread across the image, all pointing the same way, but then they would be a bit small, especially on smaller images. The centre of the Orientation cross hairs has no meaning in relation to the underlying image data or the later analysis.

Slice Geometry does exactly what you ask for by default. It calls the in-plane centre of mass/balance, calculated from the 2D location and optionally the values of the pixels, the ‘centroid’. Which I agree is a little confusing because Moments calls the 3D centre of mass the centroid too, but this will usually be in a different place.

To check that Slice Geometry is doing what you expect, turn on the annotation option. The centroid used for calculation of I, Z and J is marked as an open circle on a copy of the slice data.


#3

Aha, I see. Now I feel certain that it’s exactly what I need. Thank you so much!!!


#4

I’fe found out that if I just choose “Orientation”, it says “Unable to load plugin, possibly because it is not public”. However, “Orientation” works if I choose “Slice Geometry” (and close it to make the “Orientation” window active) without previous aligning by “Moments of Inertia”. How to make “Orientation” working without “Slice Geometry”?