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‎Data_science/Mathematica/SignalProcessing/MachineVision/RANSAC/RANSACPointAlignment.vb‎

Lines changed: 46 additions & 33 deletions
Original file line numberDiff line numberDiff line change
@@ -69,11 +69,7 @@ Imports std = System.Math
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''' A static utility class for aligning two 2D polygons using the RANSAC algorithm.
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''' This version is optimized for correctness and includes a proper least-squares refinement step.
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''' </summary>
72-
Public NotInheritable Class RANSACPointAlignment
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Private Sub New()
75-
' Prevent instantiation of this static class
76-
End Sub
72+
Public Module RANSACPointAlignment
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''' <summary>
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''' Aligns a source polygon to a target polygon using RANSAC.
@@ -83,10 +79,10 @@ Public NotInheritable Class RANSACPointAlignment
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''' <param name="iterations">The number of RANSAC iterations.</param>
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''' <param name="distanceThreshold">The distance threshold to consider a point an inlier.</param>
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''' <returns>The best-fit Transform object.</returns>
86-
Public Shared Function AlignPolygons(sourcePoly As Polygon2D,
87-
targetPoly As Polygon2D,
88-
Optional iterations As Integer = 1000,
89-
Optional distanceThreshold As Double = 0.1) As AffineTransform
82+
Public Function AlignPolygons(sourcePoly As Polygon2D,
83+
targetPoly As Polygon2D,
84+
Optional iterations As Integer = 1000,
85+
Optional distanceThreshold As Double = 0.1) As AffineTransform
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' Pre-check: need at least 3 points
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If sourcePoly.length < 2 OrElse targetPoly.length < 2 Then
@@ -156,7 +152,7 @@ Public NotInheritable Class RANSACPointAlignment
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''' <summary>
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''' Generates a list of candidate matches by finding the nearest neighbor in descriptor space.
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''' </summary>
159-
Private Shared Function GenerateCandidateMatches(ByRef sourceDesc As PointWithDescriptor(), ByRef targetDesc As PointWithDescriptor()) As List(Of (source As PointF, target As PointF))
155+
Private Function GenerateCandidateMatches(ByRef sourceDesc As PointWithDescriptor(), ByRef targetDesc As PointWithDescriptor()) As List(Of (source As PointF, target As PointF))
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Dim matches As New List(Of (source As PointF, target As PointF))()
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Call $"Generates a list of candidate matches by finding the nearest neighbor in descriptor space.".debug
@@ -195,8 +191,8 @@ Public NotInheritable Class RANSACPointAlignment
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''' <summary>
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''' Computes an affine transform from exactly three point pairs.
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''' </summary>
198-
Private Shared Function ComputeAffineFrom3Pairs(p1 As PointF, p2 As PointF, p3 As PointF,
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q1 As PointF, q2 As PointF, q3 As PointF) As AffineTransform
194+
Private Function ComputeAffineFrom3Pairs(p1 As PointF, p2 As PointF, p3 As PointF,
195+
q1 As PointF, q2 As PointF, q3 As PointF) As AffineTransform
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' Solve the linear system for 6 parameters (a,b,c,d,e,f)
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' |x1 y1 1 0 0 0| |a| |x'1|
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' |x2 y2 1 0 0 0| |b| |x'2|
@@ -205,25 +201,31 @@ Public NotInheritable Class RANSACPointAlignment
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' |0 0 0 x2 y2 1| |e| |y'2|
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' |0 0 0 x3 y3 1| |f| |y'3|
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' We can solve this by splitting it into two 3x3 systems.
208-
Dim sourceX = {p1.X, p2.X, p3.X}
209-
Dim sourceY = {p1.Y, p2.Y, p3.Y}
210-
Dim targetX = {q1.X, q2.X, q3.X}
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Dim targetY = {q1.Y, q2.Y, q3.Y}
204+
' Dim sourceX = {p1.X, p2.X, p3.X}
205+
' Dim sourceY = {p1.Y, p2.Y, p3.Y}
206+
' Dim targetX = {q1.X, q2.X, q3.X}
207+
' Dim targetY = {q1.Y, q2.Y, q3.Y}
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' Using the same least squares solver for the exact case
214-
Dim pairs As New List(Of (source As PointF, target As PointF)) From {
215-
(p1, q1), (p2, q2), (p3, q3)
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}
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Dim pairs As (source As PointF, target As PointF)() = {(p1, q1), (p2, q2), (p3, q3)}
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Dim a, b, c, d, e, f As Double
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SolveLeastSquaresAffine(pairs, a, b, c, d, e, f)
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220-
Return New AffineTransform With {.a = a, .b = b, .c = c, .d = d, .e = e, .f = f}
213+
Call SolveLeastSquaresAffine(pairs, a, b, c, d, e, f)
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Return New AffineTransform With {
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.a = a,
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.b = b,
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.c = c,
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.d = d,
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.e = e,
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.f = f
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}
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End Function
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''' <summary>
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''' Refines the transformation using all inliers with a least-squares fit for an affine transform.
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''' </summary>
226-
Private Shared Function RefineTransformWithLeastSquares(candidateMatches As List(Of (source As PointF, target As PointF)), initialTransform As AffineTransform, threshold As Double) As AffineTransform
228+
Private Function RefineTransformWithLeastSquares(candidateMatches As List(Of (source As PointF, target As PointF)), initialTransform As AffineTransform, threshold As Double) As AffineTransform
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Dim inlierPairs As New List(Of (source As PointF, target As PointF))
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Dim thresholdSq = threshold * threshold
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Dim errors As New List(Of Double)
@@ -248,23 +250,32 @@ Public NotInheritable Class RANSACPointAlignment
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End If
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Dim a, b, c, d, e, f As Double
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SolveLeastSquaresAffine(inlierPairs, a, b, c, d, e, f)
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Return New AffineTransform With {.a = a, .b = b, .c = c, .d = d, .e = e, .f = f}
253+
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Call SolveLeastSquaresAffine(inlierPairs.ToArray, a, b, c, d, e, f)
255+
256+
Return New AffineTransform With {
257+
.a = a,
258+
.b = b,
259+
.c = c,
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.d = d,
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.e = e,
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.f = f
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}
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End Function
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''' <summary>
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''' Solves the least-squares problem for affine transformation parameters.
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''' This function is unchanged from your original, as it was mathematically correct.
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''' </summary>
259-
Private Shared Sub SolveLeastSquaresAffine(points As List(Of (source As PointF, target As PointF)), ByRef a As Double, ByRef b As Double, ByRef c As Double, ByRef d As Double, ByRef e As Double, ByRef f As Double)
260-
Dim n = points.Count
270+
Private Sub SolveLeastSquaresAffine(ByRef points As (source As PointF, target As PointF)(), ByRef a As Double, ByRef b As Double, ByRef c As Double, ByRef d As Double, ByRef e As Double, ByRef f As Double)
271+
Dim n As Integer = points.Length
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Dim sumX, sumY, sumX2, sumY2, sumXY, sumXp, sumYp, sumXpX, sumXpY, sumYpX, sumYpY As Double
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263274
For Each pair In points
264-
Dim x = pair.source.X
265-
Dim y = pair.source.Y
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Dim xp = pair.target.X
267-
Dim yp = pair.target.Y
275+
Dim x As Double = pair.source.X
276+
Dim y As Double = pair.source.Y
277+
Dim xp As Double = pair.target.X
278+
Dim yp As Double = pair.target.Y
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269280
sumX += x : sumY += y
270281
sumX2 += x * x : sumY2 += y * y : sumXY += x * y
@@ -283,15 +294,17 @@ Public NotInheritable Class RANSACPointAlignment
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284295
' Solve two 3x3 systems (one for x', one for y')
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Dim det = ata_00 * (ata_11 * ata_22 - ata_12 * ata_21) -
286-
ata_01 * (ata_10 * ata_22 - ata_12 * ata_20) +
287-
ata_02 * (ata_10 * ata_21 - ata_11 * ata_20)
297+
ata_01 * (ata_10 * ata_22 - ata_12 * ata_20) +
298+
ata_02 * (ata_10 * ata_21 - ata_11 * ata_20)
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289300
If std.Abs(det) < 0.000000001 Then
290301
' Matrix is singular, cannot solve, return identity
291302
a = 1 : b = 0 : c = 0
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d = 0 : e = 1 : f = 0
304+
293305
Return
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End If
307+
295308
Dim invDet = 1.0 / det
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297310
Dim inv_00 = (ata_11 * ata_22 - ata_12 * ata_21) * invDet
@@ -313,4 +326,4 @@ Public NotInheritable Class RANSACPointAlignment
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e = inv_10 * atb_3 + inv_11 * atb_4 + inv_12 * atb_5
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f = inv_20 * atb_3 + inv_21 * atb_4 + inv_22 * atb_5
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End Sub
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End Class
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End Module

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