Transforming an array of points

AdamB

If you're applying the same transform to all the points, generally you'd be better off both in performance and accuracy with changing the container entity's transform rather than changing the Points themselves.

TIG

The two entities transform methods will affect instances/groups, faces, edges and vertices, but NOT points.
Points have their own methods .transform(trans) and .transform!(trans). and .offset(vector) and .offset!(vector) [you can use an optional second argument for 'distance' if the 'vector' is not the required length]
If you have some points that need simple offsets by a fixed vector then iterating them with offset! will do, but if you want to do a rotate/scale etc then you need an appropriate transformation...

If you clarifies what you have and what you want to end up with then more precise help might be available...

jolran

TIG.
I think this thread is related.
http://sketchucation.com/forums/viewtopic.php?f=180&t=54786

Actually the topic title describes the question quite good..

jolran

@unknownuser said:

You probably already know this, but you can traverse the points this way:
pt = mesh.point_at( index )
You can then store your indexes in an array or hash and work with them instead.

Yes I know, but In my case I desired an Array of Point-arrays(polygon) from mesh simply from Calling mesh.polygons. This still mean I'll have to recollect the Points from the returning indexes, unless I'm misstaken. Maybe one can chain methods I don't know.
Havent tried that hard yet..

@unknownuser said:

If you're applying the same transform to all the points, generally you'd be better off both in performance and accuracy with changing the container entity's transform rather than changing the Points themselves.

So there is a way to group Point3d objects ? Or are you referring to the Mesh.transform ?

Garry K

Tig,

What I have are the points that describe the handrail profile (the face at the bottom of the picture). The picture is only for clarification. None of this is actually in the model at this time.

I keep the points that are in the bottom face and apply a transformation that rotates and moves a copy of the original points. These points are then added into the PolygonMesh.

In this case there are 53 points that describe the handrail profile (could be any profile).
And there are going to be 39 filled in segments.

Currently I am applying this transform to each point:

t = Geom::Transformation.new( [ 0, 0, i * rise_per ] ) *
Geom::Transformation.rotation( [0, 0, 0], Z_AXIS, ( i * deg ).degrees )

profile.each { |val| mesh.add_point( val.transform( t ) ) }

This example puts 2120 points into the mesh 40 * 53 = 2120

I have tried adding the first profile into a second polygon mesh so that I can apply a bulk transform. It works - but the entire operation is much slower than just transforming one point at a time.

All I am trying to do is see if there is a faster way than I am doing - or if this is "as good as it gets"

Hopefully this is sufficient clarification.

Handrail Profile

Chris Fullmer

@tig said:

The two entities transform methods will affect instances/groups, faces, edges and vertices, but NOT points.

Wow, its beena while since I used those methods, apparently I had forgotten that. I guess I'm transforming vertices in my script then.

Sorry for the bad advice

tt_su

@garry k said:

Currently I am applying this transform to each point:

t = Geom::Transformation.new( [ 0, 0, i * rise_per ] ) *
Geom::Transformation.rotation( [0, 0, 0], Z_AXIS, ( i * deg ).degrees )

profile.each { |val| mesh.add_point( val.transform( t ) ) }

What if you use PolygonMesh.transform! ?

<span class="syntaxdefault"><br /></span><span class="syntaxcomment">#&nbsp;Use&nbsp;for&nbsp;in&nbsp;loop&nbsp;at&nbsp;that&nbsp;doesn't&nbsp;create&nbsp;new&nbsp;local&nbsp;object&nbsp;per&nbsp;iteration.<br />#&nbsp;Creating&nbsp;objects&nbsp;in&nbsp;Ruby&nbsp;is&nbsp;slow&nbsp;-&nbsp;so&nbsp;try&nbsp;to&nbsp;reuse&nbsp;them.<br /></span><span class="syntaxkeyword">for&nbsp;</span><span class="syntaxdefault">point&nbsp;in&nbsp;profile<br />&nbsp;&nbsp;mesh</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">add_point</span><span class="syntaxkeyword">(</span><span class="syntaxdefault">point</span><span class="syntaxkeyword">)<br /></span><span class="syntaxdefault">end<br /><br />t&nbsp;</span><span class="syntaxkeyword">=&nbsp;</span><span class="syntaxdefault">Geom</span><span class="syntaxkeyword">;;</span><span class="syntaxdefault">Transformation</span><span class="syntaxkeyword">.new(&nbsp;[&nbsp;</span><span class="syntaxdefault">0</span><span class="syntaxkeyword">,&nbsp;</span><span class="syntaxdefault">0</span><span class="syntaxkeyword">,&nbsp;</span><span class="syntaxdefault">i&nbsp;</span><span class="syntaxkeyword">*&nbsp;</span><span class="syntaxdefault">rise_per&nbsp;</span><span class="syntaxkeyword">]&nbsp;)&nbsp;*<br /></span><span class="syntaxdefault">Geom</span><span class="syntaxkeyword">;;</span><span class="syntaxdefault">Transformation</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">rotation</span><span class="syntaxkeyword">(&nbsp;[</span><span class="syntaxdefault">0</span><span class="syntaxkeyword">,&nbsp;</span><span class="syntaxdefault">0</span><span class="syntaxkeyword">,&nbsp;</span><span class="syntaxdefault">0</span><span class="syntaxkeyword">],&nbsp;</span><span class="syntaxdefault">Z_AXIS</span><span class="syntaxkeyword">,&nbsp;(&nbsp;</span><span class="syntaxdefault">i&nbsp;</span><span class="syntaxkeyword">*&nbsp;</span><span class="syntaxdefault">deg&nbsp;</span><span class="syntaxkeyword">).</span><span class="syntaxdefault">degrees&nbsp;</span><span class="syntaxkeyword">)<br /></span><span class="syntaxdefault">mesh</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">transform</span><span class="syntaxkeyword">!(&nbsp;</span><span class="syntaxdefault">t&nbsp;</span><span class="syntaxkeyword">)<br />&nbsp;</span><span class="syntaxdefault"></span>

Then you should be able to do bulk transformation of the points by doing iterative transformation for each profile step. I've never tested the performance for that - but generally the fewer operations the faster.

Garry K

I just tried your suggestion of using an incremental transform as opposed to a differential transform ( point by point from profile )

I change my timing so that it avoids the start up code which is the same for both strategies and I also avoided the smoothing algorithm on the entity after fill_from_mesh.

I performed the benchmarks 12 times for each strategy and threw out the highest and the lowest.

This resulted in a 3% improvement using the incremental transform over the point by point transform.

Incremental 0.1043
0.129
0.107
0.106
0.106
0.106
0.105
0.104
0.104
0.104
0.104
0.097
0.095

Differential 0.1077
0.131
0.112
0.111
0.109
0.109
0.108
0.108
0.107
0.106
0.104
0.103
0.101

I would still be in favor of the differential as the incremental will be prone to a slight fp (floating point) shift. It may not be noticeable with only 40 segments - but then neither is 3/1000 of a second!!

I did change the "profile.each" to a "for pt in profile" and that hardly made a difference.

So bottom line is that the bulk transform of points using a mesh is slightly faster - however it is more complex and most likely requires more memory. But it is certainly something to consider as a viable option in some circumstances!

tt_su

The data set you currently work with is probably so small that you won't gain that much. But I'd think as the data set increases you'd see bigger and bigger differences.

Garry K

That is why I suggested it would be a viable option in some circumstances.

I think that we gain performance in the actual transform but may loose it accessing the points in the mesh.

If there was a bulk operation to move points from one mesh to another without invoking the built in check - then you would probably benefit even on a smaller data set.

Dan Rathbun

@jolran said:

So there is a way to group Point3d objects ?

Yes there is. Create a Geom::BoundingBox object and add points to it.

However I do not see a transform method that applies to bounding boxes.

jolran

@unknownuser said:

Yes there is. Create a Geom::BoundingBox object and add points to it.
However I do not see a transform method that applies to bounding boxes

Forgot about that one. Will be useful, even if not in this case.

@unknownuser said:

I think that we gain performance in the actual transform but may loose it accessing the points in the mesh.

If polygonmesh.polygons returned arrays of Points that woulden't be the case.

Have you tried recollecting points to a new Array and Transform! them in place ?
Array.Dup does not work with Point3D objects
As far as I know one have to recollect points into new Array. Comes with a timecost of course..

jolran

Ok. Did some tests and it seams like Polygonmesh transform scales quite well.

Note this test may not be constructed optimaly, I'm still green. But still quite interesting to see how fast polygonMesh transforms many Points.
The test might provide different result if arrays are flattended, but I need to keep the polygon/Points hierarchy.

Edit: I saw that newlist actually don't keep the hierarchy So the result would probably be slower. Can't really Output the result in ruby consol

# Square Polygon
pts = [
  Geom;;Point3d.new(-5,-5,0),
  Geom;;Point3d.new(5,-5,0),
  Geom;;Point3d.new(5,5,0),
  Geom;;Point3d.new(-5,5,0)
]

vec = [10,0,0]
tr = Geom;;Transformation.new( vec )

# Create som polygons for testing..
polys = {}
vec2 = vec.clone
for i in 0...50
  polys[i] = pts.collect{|pt| pt.offset(vec2) }
  vec2.offset!([15,10,0])
end

# Mesh
msh = Geom;;PolygonMesh.new
for k,v in polys
  msh.add_polygon(v)
end

# Array of points
polygonials = polys.values
puts "total nr Point3dObjects; #{polygonials.flatten.length}"

#group = Sketchup.active_model.active_entities.add_group
#group.entities.fill_from_mesh(msh, true, 12)

#Tests On My computer Gave;
#PolygonMesh Transforms; 0.03
#Array Transforms; 1.052
#Array Transforms And Collect; 2.335

start = Time.now
10000.times {
    msh.transform!(tr)
}
puts "PolygonMesh Transforms; #{Time.now - start}"


start = Time.now
10000.times {
for list in polygonials
  for p in list do p.transform!(tr) end
end
}
puts "Array Transforms; #{Time.now - start}"

start = Time.now
newlist = []
10000.times {
for list in polygonials
  newlist << list.collect{|p| p.transform(tr) }
end
}
puts "Array Transforms And Collect; #{Time.now - start}"

Garry K

What about a benchmark for a hash?

jolran


start = Time.now
10000.times {
for key,val in polys
  for p in val do p.transform!(tr) end
end
}
puts "Nested Hash Transforms; #{Time.now - start}" # => 1.274

It is a Hash? If I don't nest the Hash the "polygon-Points" relation will be impossible to retrieve afterwards:
Hash = { 0 => [pt,pt,pt,pt] etc }

Do you mean 1 layer Hash structure { key => pointd3d etc } ?

There may off course be better structures for this, I'm all ears.

Edit: I tried running each test separately muting the other timers with following result:

PolygonMesh Transforms: 0.047
Nested Hash Transforms: 1.191
Array Transforms: 1.066
Array Transforms And Collect: 2.328

Maybe I'm confusing the matter... And I haven't outputed the resulting mesh(which would stall Sketchup) so there is a matter of knowing if the resulting Mesh is qualified as well.

jolran

Ah you mean put result in Hash ?

start = Time.now
newHash = {}
10000.times {
for i in 0...polygonials.length
  newHash[i] = polygonials[i].collect{|p| p.transform(tr) }
end
}
puts "HASH Transforms And Collect; #{Time.now - start}"

=>2.381

Garry K

You could render the mesh after the timers to maintain benchmark validity.

Have you tried traversing your polygons?
mesh.polygon_points_at( index )
Shouldn't this give you the same results as an outer_loop on a face?
The question I would have is although you can get the points for each polygon - Is there a way to tie in a reference to the faces in the model once you have rendered the mesh?
I would hope that the entities in the group immediately after a fill_from_mesh would be in mesh polygon index order. So there should be a 1 to 1 relationship.

I haven't played with hashes yet - so my question is probably confusing to you. Although I've programmed for many years and also played with CAD for many years I've only logged 3 or so months with Sketchup since I got serious about it (guess I caught the Sketchup virus).

jolran

@unknownuser said:

You could render the mesh after the timers to maintain benchmark validity.

Yeah, for those tests that edit in Place. Otherwise it would be too intense for Sketchup.

@unknownuser said:

The question I would have is although you can get the points for each polygon - Is there a way to tie in a reference to the faces in the model once you have rendered the mesh?

I'm just moving Points in this code. I reckon you'd have to recollect faces afterwards
and do some boolean tests. There's normal_at which could be used for ex.
It all depends on (referring to your other question) if face order == polygon index order. I should test that as well unless someone else already knows..

I'm pretty new to programming, so there can be lots of holes in the logic of my tests.
But what better way to learn than trying to solve a problem, right?

Hashes in Ruby are supposed to have much faster lookup than arrays. I think that's what Thomthom tried to point out earlier.

tt_su

@garry k said:

I think that we gain performance in the actual transform but may loose it accessing the points in the mesh.

Geom::PolygonMesh.points? http://www.sketchup.com/intl/en/developer/docs/ourdoc/polygonmesh.php#points

Garry K

Sorry - bad terminology. I was talking read and write access.
the only write access we have is mesh.add_point.
I'm still thinking as a C / C++ programmer.