Transforming an array of points

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.

tt_su

@garry k said:

Sorry - bad terminology. I was talking read and write access.
the only write access we have is mesh.add_point.

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

jolran

Yet Another test

Don't know how reliable this test is but it appears face get appended in the same order as indexed in Polygonmesh. But Polygonmesh Count indexes starting at 1.

Edit: Updated for adding c_point in polygonmesh index as well. But wonder how hidden edges affect the Index ordering..

The API says:

@unknownuser said:

The negative values should not be used as an index for point_at, take the positive value of the index value in the polygon array

Perhaps hidden edges will only happend if mesh is constructed from a collection of Sketchup::Face's. Not relevant in this case.
In that case maybe use index.abs or perhaps double negation: index = index<0 ? -index : index

ents = Sketchup.active_model.active_entities

def centerpoints(f)
  cx = (f[0].x + f[1].x + f[2].x + f[3].x)/4
  cy = (f[0].y + f[1].y + f[2].y + f[3].y)/4
  cz = (f[0].z + f[1].z + f[2].z + f[3].z)/4
  return Geom;;Point3d.new(cx, cy, cz)
end


face1 = [ 
  Geom;;Point3d.new(-5,-5,0), Geom;;Point3d.new(5,-5,0),
  Geom;;Point3d.new(5,5,0), Geom;;Point3d.new(-5,5,0) 
]

#create points for 4 faces
faceHash = {}
for i in (0...4) 
   faceHash[i] = face1
   face1 = face1.collect{|pt| pt.offset([20,0,0])}
end

#get refference to the center of "face"#3 Before appending to mesh.

fC = centerpoints(faceHash[2])
ents.add_cpoint(fC)

# Bit strange to loop hash this way, but they get ordered.
msh = Geom;;PolygonMesh.new
for n in (0...faceHash.length)
  msh.add_polygon(faceHash[n])
end

#Test PolygonMesh index. How does hidden edges affect indexes for this ?
# +1 index for polygons in Mesh. 2 c_points should get added at same spot
meshface3 = msh.polygon_points_at(2+1)
mc = centerpoints(meshface3)
ents.add_cpoint(mc)


group = ents.add_group
group.entities.add_faces_from_mesh(msh)
faces = group.entities.grep(Sketchup;;Face)

#Red material to face 3
faces[2].material = "red"