Coordinates of CoM

Hi Soeren,
I build a new model for the arm movement where I use the new files you
uploaded. Now I want to scale another model to the AnyBody size and
therefore I look for exact coordinates again. Normally no problem but
in this model there are difficulties: for the humerus segment I need
the origin, the joint coordinates and the CoM coordinates. When I
click through the window next to the texteditor I get the values for
the origin, but I don´t find the definition of this origin. But that´s
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 coordinates.
I definied it like this:

sCoM={0,-0.18Length,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.HumanModel.Right.ShoulderArm.Seg.Humerus.r = {0.01868401,
0.4146685, 0.1929215};

Main.Model.HumanModel.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 before!

But AnyBody calculates:
ain.Model.HumanModel.Right.ShoulderArm.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 AnyVec3
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

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@yahoogroups.com, “Maren” <anystarter@…> wrote:
>
> Hi Soeren,
> I build a new model for the arm movement where I use the new files
you
> uploaded. Now I want to scale another model to the AnyBody size and
> therefore I look for exact coordinates again. Normally no problem
but
> in this model there are difficulties: for the humerus segment I
need
> the origin, the joint coordinates and the CoM coordinates. When I
> click through the window next to the texteditor I get the values
for
> the origin, but I don´t find the definition of this origin. But
that´s
> 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
coordinates.
> I definied it like this:
>
> sCoM={0,-0.18Length,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.HumanModel.Right.ShoulderArm.Seg.Humerus.r =
{0.01868401,
> 0.4146685, 0.1929215};
>
> Main.Model.HumanModel.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
before!
>
> But AnyBody calculates:
> ain.Model.HumanModel.Right.ShoulderArm.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
AnyVec3
> 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
>