Who told you that? The Z-filter algorithm might result in an off center plot if guiding starts with the star off center and a large X-factor is used. This happens because it works in the frequency domain and a constant offset corrresponds to zero frequency so it does not get corrected. But it does not necessarily result in a 1 arc-second shift under all conditions. In fact, it is arguably preferable for the offset to be retained as it results in a better image.
fmozza wrote: During my session, I noticed an issue with calculating RMS. I used PHD2 for guiding, and I use the Z-filter algorithm for DEC control. According to the folks at PHD2, when Z-filter is used, PHD2 shifts the image - RA is centered, but DEC is shifted by 1 arc-second. I'm not sure why, but this will throw off the calculation of RMS due to the DEC shift. Take a look at the attached pictures so you can see what I mean.
But very nice tool!
This should be a really useful tool. Great work!
hy wrote: This is what Analyze currently does re RMS guide error. Please let me know if you think I got something wrong.
Internal guider, see
SquareError(t) = ((RA(t) - RA_target(t))**2 + (DEC(t) - DEC_target(t))**2)
In the PHD2 case, the RA(t) - RA_target(t) or diff_ra_arcsecs is taken straight from PHD2 (PHD2 calculates that and sends it to Ekos).
See invent.kde.org/education/kstars/-/blob/m...lguide/phd2.cpp#L487 for PHD2 part.
So, in the PHD2 case, Ekos is taking as the RA or DEC error, what PHD2 says is the RA or DEC error.
Analyze implements an IIR filter with an approximate time constant of 40 samples (nothing magic about 40 samples == about 2 minutes with 3s samples)
filteredRMS = 0;
constexpr double timeConstant = 40.0;
rmsFilterAlpha = 1.0 / pow(timeConstant, 0.865);
// at every time sample (x below is SquareError(t) above)
filteredRMS = rmsFilterAlpha * x + (1.0 - rmsFilterAlpha) * filteredRMS;
and takes the sqrt of the (poorly named) filteredRMS to get the rms value you see. (I guess I should have named it filteredSquareError).
It does not take the mean of the RA or DEC samples. I understand your logic, though, why that might be nice.
All that said, that's not quite true for the case of RMS error printed in the Details box, e.g. when you click on a guide timeline session or a capture timeline session.
There, it does not use an approximate IIR filter, but rather computes exactly the sqrt of the sum of the square error in the interval.
In any event, just to be clear, this is what is currently implemented.
Happy to entertain suggestions,
fenriques wrote: awesome work! thank you. All the insight needed to monitor and review the session in one window; to me it should replace the Setup tab.
@Rick, I'm thinking to use the .analyze file as the only source of information for Astrodom. What do you think?