AW: Re: Coordinates of CoM

Hi Soeren, just five minutes ago I found the same soluten after I added up the
single distances between the local Ref and the absolute coordinates for CoM.
Thank you very much, now it´s clearer and I now know what this Offset is. With
best regards, Maren

----- Ursprüngliche Mail ----
Von: AnyBody Support <>
Gesendet: Mittwoch, den 2. August 2006, 14:59:52 Uhr
Betreff: [anyscript] Re: Coordinates of CoM

                        Hi Maren

Your assumption of the expected position of Show_sCom to be

(0.01868401, 0.35346004, 0.1929215)

is only correct if the local cooridnate system of the humerus
segment is 100% alligned with the global ref system, if this is the
case then your are right. In the present case the orientation of
humerus segment is slightly out of allignment so a translation of -
0.061 along the local y axis of the segment will also produce a
small movememt in the global x and z coordinates because the axes
are not alligned. I think this is why you do not get the constant x
and z values you expected.

The Offset value has been used to translate the nodes of the segment
by a certain amount, i do not think it will have any influence here.

So to summarize:
sCom is given in the local coordinate system of the segment
You can find the r value of Com as the r vector of the Show_Com node

I hope this made it more clear, otherwise please do not hesitate to
write again.

Best regards
Søren, AnyBody Support

— In anyscript@yahoogrou, “Maren” <anystarter@ …> wrote:
> Hi Soeren,
> I build a new model for the arm movement where I use the new files
> uploaded. Now I want to scale another model to the AnyBody size and
> therefore I look for exact coordinates again. Normally no problem
> in this model there are difficulties: for the humerus segment I
> the origin, the joint coordinates and the CoM coordinates. When I
> click through the window next to the texteditor I get the values
> the origin, but I don´t find the definition of this origin. But
> not my problem. The joint coordinates were easy to find, after a
> kinematic analysis I got nice values.
> But now my question:
> The variable “sCoM” is defined in relative coordinates. When I
want to
> know the absolute coordinates I define a RefNode with the same
> coordinates like sCoM and after loading and running a kinematic
> analysis again I can click in the window next to the text editor to
> get “r”. I tried it for the Humerus segment but the absolute values
> for this sCoM node doesn´t fit with the origin+relative
> I definied it like this:
> sCoM={0,-0.18* Length,0} ; //given by the model
> AnyRefNode show_sCOM= //defined by myself
> {
> sRel = {0,-0.18*.Length, 0};
> AnyDrawRefFrame sCOM=
> {
> RGB = {1,0,0}; //rot
> ScaleXYZ = {0.3, 0.3, 0.3};
> };
> };
> Here are the values I get for r, sCoM and abs. sCoM:
> Main.Model.HumanMod el.Right. ShoulderArm. Seg.Humerus. r =
> 0.4146685, 0.1929215};
> Main.Model.HumanMod el.Right. ShoulderArm. Seg.Humerus. sCoM = {0,
> -0.06120846, 0};
> In my opinion this has to give the absolute coordinates for sCoM:
> (0.01868401, 0.35346004, 0.1929215) > x and z were the same as
> But AnyBody calculates:
> ain.Model.HumanMode l.Right.Shoulder Arm.Seg.Humerus. show_sCOM. r =
> {0.02399838, 0.353925, 0.1982561};
> Now I´m confused. Where is r for the humerus segment defined? Which
> coordinate system is sCoM defined relative to? What does the
> Offset mean? ( I uploaded the model named Armmodell04) Does this
> Offset influence the coordinates of sCoM? What´s his job? How do I
> have to calculate if I want to know the absolute coordinates of the
> CoM? I hope you can solve my confusion.
> Thank you very much and with best regards, Maren

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