# Determine if any existing obs packages have a flip from PIXELS->FOCAL

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## Details

• Type: Story
• Status: Done
• Resolution: Done
• Fix Version/s: None
• Component/s:
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• Story Points:
1
• Sprint:
AP F19-1
• Team:

## Description

To better understand RFC-605, we need to determine if any of our existing obs packages have a flip in their pixel->focal transform. We think they are all defined as looking "down" on the focal plane, but we need to check.

1. Load the cameraGeom for each obs package.
2. Compute determinant of pixel->focal transform.
3. If determinant is negative, there is a flip.

## Attachments

1. pixelDeterminant.py
2 kB

## Activity

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John Parejko added a comment -

Jim Bosch: Please take a look at the attached code. You can run it with lsst_distrib setup, and it should print out the determinant for each of the detectors on each included camera. All are positive definite. I think I got the math right, but can you please check (note the shape of the matrix returned by linearApprox)?

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John Parejko added a comment - Jim Bosch : Please take a look at the attached code. You can run it with lsst_distrib setup, and it should print out the determinant for each of the detectors on each included camera. All are positive definite. I think I got the math right, but can you please check (note the shape of the matrix returned by linearApprox )?
Hide
Jim Bosch added a comment -

I was too lazy to try to figure out Mapping::linearApprox's wonky conventions (but I trusted Russell Owen to have done so), and just modified the script to use

 np.linalg.det(trans.getJacobian(point))

and reran it. That gave me the same result you got (no flips), and that's good enough for me.

Show
Jim Bosch added a comment - I was too lazy to try to figure out Mapping::linearApprox 's wonky conventions (but I trusted Russell Owen to have done so), and just modified the script to use np.linalg.det(trans.getJacobian(point)) and reran it. That gave me the same result you got (no flips), and that's good enough for me.
Hide
John Parejko added a comment -

Thanks. Given that we agree, and there is some attached code we can fall back on if necessary, I think we can close this.

Show
John Parejko added a comment - Thanks. Given that we agree, and there is some attached code we can fall back on if necessary, I think we can close this.

## People

• Assignee:
John Parejko
Reporter:
John Parejko
Reviewers:
Jim Bosch
Watchers:
Chris Morrison, Jim Bosch, John Parejko, John Swinbank, Lauren MacArthur, Russell Owen
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Watchers:
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## Dates

• Created:
Updated:
Resolved: