<div dir="ltr"><div>Jim, do you have any thoughts on how you'd rather communicate the transformation result of ICP (whatever we settle on)? What would be more user friendly?</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Mar 6, 2020 at 10:24 AM Jim Klassen <<a href="mailto:klassen.js@gmail.com">klassen.js@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div bgcolor="#FFFFFF">
<div dir="auto">I suspect we could compose it three operations into
a single transform matrix, but probably at a loss of precision.
(I suspect preserving precision this is why filters.icp bothers
with calculating and shifting to the centroid in the first place).<br>
<div dir="auto"><br>
Alternatively, it might be simpler for the user if the centroid
value and matrix could be passed directly into filters.transform
(instead of needing three filters.transforms in the pipeline).<br>
<br>
In my opinion, the current workflow of saving the metadata,
manually parsing it, and then constructing a new pipeline with
values from the metadata isn't very user friendly in general.
If this was something I was doing regularly, I would certainly
write a script do those steps for me (probably as part of a
larger workflow). And if a script is generating the second
pipeline, it doesn't really matter to me if the second pipeline
is one stage or three stages.<br>
<br>
I have a first pass at a PR here:<br>
<a href="https://github.com/PDAL/PDAL/pull/2962" target="_blank">https://github.com/PDAL/PDAL/pull/2962</a><br>
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<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Fri, Mar 6, 2020, 08:47
Bradley Chambers <<a href="mailto:brad.chambers@gmail.com" target="_blank">brad.chambers@gmail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="ltr">
<div>
<div>
<div dir="auto">I’m wondering if it would make more sense
to simply compose the three steps into a single output
transformation. Making the user do the three steps
themselves seems overly complicated. Is there a scenario
in which we only want the transformation of the centered
clouds (current state of the code)? Your use case is
probably more common. </div>
</div>
</div>
</div>
<div>
<div><br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Thu, Mar 5, 2020 at
18:53 Jim Klassen <<a href="mailto:klassen.js@gmail.com" rel="noreferrer" target="_blank">klassen.js@gmail.com</a>> wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div>
<p>Does a strategy of adding the centroid to the
filters.icp metadata and updating filters.icp
documentation with the pipeline to apply it sound
good?<br>
</p>
</div>
<div>
<div>On 3/5/20 5:41 PM, Andrew Bell wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">This seems the same as this already
reported bug:
<div><br>
</div>
<div><a href="https://github.com/PDAL/PDAL/issues/2939" rel="noreferrer" target="_blank">https://github.com/PDAL/PDAL/issues/2939</a><br>
</div>
<div><br>
</div>
<div>If you want to submit a PR, I'll look it
over.</div>
<div><br>
</div>
<div>Thanks!</div>
<div><br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Thu, Mar 5,
2020 at 6:36 PM Jim Klassen <<a href="mailto:klassen.js@gmail.com" rel="noreferrer" target="_blank">klassen.js@gmail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">I am trying
to do something similar (apply ICP on a subset
of a large <br>
dataset) and am running into confusion over the
transformation matrix in <br>
the metadata.<br>
<br>
The point cloud output of the ICP filter on the
subset looks good. <br>
However when I try to use the resulting
"transform" metadata as a input <br>
into filters.transformation.matrix over the full
dataset, the resulting <br>
transformation moves the points wildly out of
position.<br>
<br>
Looking at the code, in
IterativeClosestPoint.cpp, it looks like the <br>
transformation matrix (T) is applied after
shifting the point cloud to <br>
the centroid of the reference point cloud (C),
and the shifted back to <br>
regular coordinates.<br>
<br>
So something like Pout = ((P - C) * T) + C<br>
<br>
Where P is a 4 element input point vector
(x,y,z,1), Pout is the output <br>
point vector, C is the centroid vector
(x,y,z,0), T is the 4x4 <br>
transformation matrix found by ICP.<br>
<br>
T is reported in the metadata for the stage,
however, C is not reported <br>
in the metadata.<br>
<br>
But the transformation matrix that
filters.transformation expects <br>
something more like<br>
<br>
Pout = P * T'<br>
<br>
If C is not (0,0,0) then T and T' will be
different.<br>
<br>
I modified IterativeClosestPoint.cpp to also
export the centroid to the <br>
metadata and then created a pipeline with three
transformations, first <br>
shifting by the negative of the centroid, then
applying T, then shifting <br>
back by the centroid and that produced the
expected results.<br>
<br>
<br>
On 2/18/20 7:24 PM, Bradley Chambers wrote:<br>
> The options are very heavily borrowed from
the PCL library, where this <br>
> was a squared value. Also, keep in mind
that the default values may be <br>
> better suited for terrestrial/robotics
applications (as opposed to <br>
> aerial), and will very likely need some
tweaking.<br>
><br>
> The reported transformation should also be
reported in row major <br>
> order, like the transformation filter. If
you find it is not, I’d <br>
> consider that a bug, so feel free to file a
ticket.<br>
><br>
> PRs are always welcome, especially for
documentation!<br>
><br>
> Brad<br>
><br>
<br>
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<br clear="all">
<div><br>
</div>
-- <br>
<div dir="ltr">Andrew Bell<br>
<a href="mailto:andrew.bell.ia@gmail.com" rel="noreferrer" target="_blank">andrew.bell.ia@gmail.com</a></div>
</blockquote>
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