Sorry for using too large attachments with the previous copy of my message.
Erik Butchert
-------- Original Message ----------
From: butchert erik <[email protected]>
To: [email protected]
Date: 09 April 2017 at 17:51
Subject: RE: [Pdl-general] 2d rigid transformation
Hi
Perhaps I can explain my issue better if I send you a copy of part of one of the
text files I get from the co-ordinate measuring instrument (attached). The rows
are the data for each hole in a test piece for assessing XY accuracy of a
drilling machine.
Column 1 is the hole number
2 is the X program position
3 is the X measured position
4 is the X error
5, 6 and 7 are the same but for the Y axis
You can ignore the rest for the purposes of this exercise.
The problem is that when the test piece is aligned to the measuring machine it
uses 2 drilled holes that have the same programmed X (or Y) position to
establish a line parallel to the instrument axis, but of course there’s nothing
magical about these “datum” holes they are as inaccurate as any other hole, this
skews the panel against the CMM axes so the measured positions become more
inaccurate as the distance from the constructed origin increases. What I am
trying to get to is to calculate the best fit of the measured values to the
programmed ones, and therefor the X,Y positions with the alignment error
removed. If you examine the Xerror v Yerror plot in the pdf you will see instead
of being round it is elongated in the Y axis,as typically the test piece is
longer in the Y than in the X so I wonder how much of this is rotational error.
I can see references to the problem such as
https://elonen.iki.fi/code/misc-notes/2d-rigid-fit/
https://elonen.iki.fi/code/misc-notes/2d-rigid-fit/
but haven’t found anything similar within Perl/PDL
BTW I use PDL’s extracted from the measurement files and GnuPlot to show very
useful interactive plots so to be able to build the alignment correction within
the existing Perl script would be a good step forward.
Erik
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Kreis
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