Reference system change (theory, not exercise solution)

[Mituga]

Hi,

my geometry sucks a little so probably I'm asking an easy question.

I have a camera sensor working in front of a person, the sensor gives me the coordinates (X, Y, Z) taking as origin of coordinates the own sensor. First of all, I perform a calibration procces which obtain the coordinates of head, feet and hands (with arms in 90º to body). With these points I calculate 3 vectors (head - feet, left hand - right hand, Cross multiplication of others). What I need is to transform the next points taken from the sensor from the original coordinates to the vector space formed by the 3 calculated vectors. The objective is to have the origin of coordinates in the feet of the person instead on the sensor.

What I prooved and think that didn't work (remember that my brain dont think in 3D so proably I'm doing stupid things):

- Substract from each point coordinates taken from the sensor the coordinates of the same point in the calibration instant (asuming that I always get the coordinates of the same parts of the body). I didn't manage to have the origin of coordinates in my feet.

- I was reading about something called "base change matrix" but for this I need to have 3 vectors representing the first vector space ( could I take (0 0 1), (0 1 0) and (1 0 0) ??) and my 3 vectors who represent the new base are expresend in the first base (is it important?) I have alot of doubts about it....

- I read also about a rotation and a transform. Each point has to be transformed and rotated to be in the new space, but I have more doubts than with the first option....


I'm not searching a direct answer, I only need someone who guides me a little or some web page where I could read about what I want to do. I'm a little desperate with this... More I read about it, more messed I feel...

Thanks.

 

[Ishuda]

Hi,

my geometry sucks a little so probably I'm asking an easy question.

I have a camera sensor working in front of a person, the sensor gives me the coordinates (X, Y, Z) taking as origin of coordinates the own sensor. First of all, I perform a calibration procces which obtain the coordinates of head, feet and hands (with arms in 90º to body). With these points I calculate 3 vectors (head - feet, left hand - right hand, Cross multiplication of others). What I need is to transform the next points taken from the sensor from the original coordinates to the vector space formed by the 3 calculated vectors. The objective is to have the origin of coordinates in the feet of the person instead on the sensor.

What I prooved and think that didn't work (remember that my brain dont think in 3D so proably I'm doing stupid things):

- Substract from each point coordinates taken from the sensor the coordinates of the same point in the calibration instant (asuming that I always get the coordinates of the same parts of the body). I didn't manage to have the origin of coordinates in my feet.

- I was reading about something called "base change matrix" but for this I need to have 3 vectors representing the first vector space ( could I take (0 0 1), (0 1 0) and (1 0 0) ??) and my 3 vectors who represent the new base are expresend in the first base (is it important?) I have alot of doubts about it....

- I read also about a rotation and a transform. Each point has to be transformed and rotated to be in the new space, but I have more doubts than with the first option....


I'm not searching a direct answer, I only need someone who guides me a little or some web page where I could read about what I want to do. I'm a little desperate with this... More I read about it, more messed I feel...

Thanks.

Suppose we have a line

0       1       2       3       4

but I want to measure from 2 instead of from 0. Then subtract 2 from each point

-2      -1      0       1       2

Suppose we have a plane

(2,0)   (2,1)   (2,2)
(1,0)   (1,1)   (1,2)
(0,0)   (0,1)   (0,2)

but want to measure from (1,1) instead of (0,0). Then subtract (1,1) from each point

( 1,-1)   ( 1,0)   ( 1,1)
( 0,-1)   ( 0,0)   ( 0,1)
(-1,-1)   (-1,0)   (-1,1)

Suppose we have a cube...