You list your options, but they're not the only ones on the table.
Sure. I didn't say the list was exhaustive, hence the etc...
As we've noted previously NIST did NOT use the NW corner to plot their data, so partially (or even mostly) for this reason the velocity curves are different.
Their choice of location and methodology is significant problem for their data...
a) They misinterpreted initial motion as vertical rather than north-south (as they did not take account of the initial twisting motion visible from the Cam#3 viewpoint).
b) They did not perform perspective correction.
c) They did not perform static point extraction (the removal of camera movement from trace data. Even though the view may
look static, it is not.)
d) They did not track a feature at all, but a horizontal position. As the building did not descent completely vertically, but included some east-west movement, their data is actually of a wandering horizontal point, not a feature on the facade.
e) In order to obtain a trace from their initial point to their stated final point they had to *splice* together two traces from completely different horizontal positions, which without taking account of the perspective and distance shearing effects makes the data further skewed.
f) They did not treat the base video data correctly, using an interlaced copy of the video (the actual copy they used is available within the recent FOIA releases. I have the original)
g) They did not perform a per-frame trace, but instead skipped frames, reducing the sampling rate considerably and reducing available data redundancy for the purposes of noise reduction and derivation of velocity and acceleration profile data.
h) They applied their interpretation to the entire north face.
i) It is highly probable they used a manual process to record the trace data, rather than the sub-pixel accurate automated feature tracing methods I employ.
These are some of the reasons their data is shoddy and their method sloppy.
Some have contended that NIST's measurements are not valid since they wall deformed, but nobody has shown to what extent it did, and how that would affect the NIST measurements - ie nobody has quantified it in an accurate way.
We have extracted a fair bit of detail on early building motion over at the911forum.
So it's rather premature, IMO, to treat the NIST measurements with the degree of contempt that Femr2 does.
I do not agree. See above. I perhaps word my distaste more emotively than necessary when folk try to reject my data in favour of theirs with absolutely no technical reasoning other than I am branded a *twoofer*.
So far his reactions are surprisingly crude, compared to the sophistication of his measurements.
My conclusions are simple. It's not rocket science.
if one doesn't focus on attacking NIST and making grandiose claims
What *grandiose claims* ? Remember the reason this topic resurfaced...discussion for cmatrix. He uses NISTSs words to support his position. It is not possible to change that position without highlighting the incorrect assertions made by NIST (which you call attacking NIST. Emotive.)
Back to the original NIST measurements of approx. 5.4s for the 18 stories to fall out of sight - I've done several measurements on multiple videos which essentially find the same thing, give or take a few frames.
Then we should discuss determination of T
0 and initial motion direction, as that is where NIST went astray.
So I side with NIST on the original '40% longer than freefall would have produced' opinion, for that reason alone.
See above.
I don't agree with Femr2 that NIST are inaccurate or incompetent or whatever other pejorative adjectives were used.
See above.
