Hi Paul.
I certainly like some of the new features in CCDI2, and I look forward to trying out the registration feature and integration with CCDStack.

Question.
I would half expect the direction of tilt given in a curvature map to be similar to that given in an aspect map.

Using the same 10 images, the amount/direction given in the curvature map is 1% at -7degrees...what does a negative figure here mean? and the amount/direction given in the aspect map was 4% at 112 degrees.

How do I interpret this?
thanks
Martin

Hi Martin,

An optical plane tilt will almost certainly create a tilt in the curvature map, but not necessarily in the aspect map (although very likely). That'll depend primarily on the type of optical system, what kind of aberrations are present, and how large the FWHM difference really is between the two sides of the tilt.

Negative degrees are just a mathematical way to express clock-wise direction. The direction normally starts at 0 degrees, which is pointing to the right. Positive degrees measure the direction counter-clock-wise from zero. So, 45 degrees points up and to the right, 90 degrees is pointing straight up, while 180 degrees is pointing left.

Negative degrees are the same, but measure clock-wise direction. So, -45 degrees points down and to the right, while -90 degrees points straight down. -180 degrees is the same as +180 degrees and points left. -90 degrees is actually the same as +270 degrees.

In your example, 1% or even 4% tilt is well below noise level for the image, as it will translate to a tiny fraction of a pixel difference in FWHM values between the two extremes in the image. That said, -7 degrees and 112 degrees point in two opposite directions of a nearly the same straight line.

One points 7 degrees down (in the clock-wise direction from zero degrees), or at about 4 o'clock. 112 degrees points points slightly left of up direction, or at about 11 o'clock. While not quite a straight line, these do indicate a similar tilt line, but different tilt directions. What that means is that aspect ratios increase in the opposite direction to the FWHM values along the same tilt line.

Hope this is not too confusing!

Let me know what you think of CCDIS registration.

Regards,


-Paul