To go back and forth from the SPARX (`psi_S,theta_S, phi_S `)convention and what Chimera records( `psi_C, theta_C, phi_C` ):

• `psi_S =  pi/2 - psi_C`

• `theta_S = theta_C`

• `phi_S = (3*pi)/2 - phi_C`

• In more detail about the relation derivation, please check the following notes ( Solution From Summer 2005):
• I created a 3 dimensional tripod with legs with three different lengths.

1. I took the tripod, saved to BRIX, and loaded into Chimera

2. Noting the original positions of the tripods legs,

• I could perform rotations around what were the original definition of the axes.

3. For each of these rotations, a, I noted the transformation recorded in Chimera as b.

• In practice, I used three rotations (positive 90 degrees about each of the original coordinate axes).

4.

• I supposed
• a = `R_alpha` b `R_beta`

for each of the rotations, a, with `R_alpha` and `R_beta` unknown but fixed.

The general solution to these sort of problems is not so easy.

But in this particular case, the problem is not quite so hard and I found (with a certain amount of guesswork):

• `R_beta  = R_alpha = 0 1 0, 1  0  0 , 0  0 -1 `

Notice that `R_beta`is its own inverse `R_beta = R_beta^(-1)` . So a = `R_beta` b `R_beta` and b = `R_beta` a `R_beta`

• Summer 2005

SparxWiki/Chimera-Brix_issue (last edited 2013-07-01 13:12:53 by localhost)