Method and apparatus for the registration of 3D ear impression models
View Patent ↗A method of designing hearing aid molds is disclosed whereby two shapes corresponding to graphical images of ear impressions are registered with each other to facilitate joint processing of the hearing aid design. In a first embodiment, a first graphical representation of a first ear impression is received and a feature, such as the aperture of the ear impression, is identified on that graphical model. A first vector is generated that represents the orientation and shape of that first feature. The three-dimensional translation and rotation of that first vector are determined that are necessary to align the first vector with a second vector representing the orientation and a shape of a feature, once again such as the aperture, of a second ear impression. In another embodiment, this alignment is then refined by minimizing the sum of the distances between points on the first and second graphical representations.
1. A method for registering a first graphical representation of a first ear impression with a second graphical representation of a second ear impression, said method comprising:
identifying an aperture of said first ear impression;
generating a first vector representing an orientation and a shape of said aperture in said first ear impression; and
determining a translation and a rotation of said first vector to achieve alignment of said first vector with a second vector representing an orientation and a shape of an aperture in said second ear impression.
2. The method of claim 1 wherein said first graphical representation comprises a first plurality of points located on a surface of said first ear impression and said second graphical representation comprises a second plurality of points located on a surface of said second ear impression.
3. The method of claim 1 wherein said first vector representing an orientation and a shape of said aperture in said first ear impression comprises a plurality of aperture points along an aperture contour line, an aperture center point, and center points of one or more canal contour lines above the aperture contour line in said first ear impression.
4. The method of claim 3 wherein said second vector representing an orientation and a shape of an aperture in said second ear impression comprises a plurality of aperture points along an aperture contour line, an aperture center point, and center points of one or more canal contour lines above the aperture contour line in said second ear impression.
5. The method of claim 2 further comprising:
removing a portion of points from said first plurality of points prior to said step of generating a first vector.
6. The method of claim 5 wherein said portion of points comprises points that are not associated with said aperture of said first ear impression.
7. The method of claim 1 wherein said translation is determined according to the expression:
∂
T
k
∂
t
=
∑
i
=
1
n
<
[
P
i
-
(
R
*
Q
i
+
T
)
]
,
∂
T
∂
T
k
>
where
∂
T
∂
T
1
=
(
1
0
0
)
,
∂
T
∂
T
2
=
(
0
1
0
)
,
∂
T
∂
T
3
=
(
0
0
1
)
and where T is a translation parameter; R is a rotation parameter; P i and Q i are points in a set of three dimensional points representing aperture vectors at contour line i of a first and a second ear impression, respectively; and k is the number of the translation parameter where kε1, 2, 3.
8. The method of claim 1 wherein said rotation is determined according to the expression:
∂
w
k
∂
t
=
∑
i
=
1
n
<
[
P
i
-
(
R
*
Q
i
+
T
)
]
,
R
*
∂
w
^
∂
w
k
Q
i
>
where
∂
w
^
∂
w
1
Q
i
=
(
0
-
Z
i
Y
i
)
,
∂
w
^
∂
w
2
Q
i
=
(
Z
i
0
-
X
i
)
,
∂
w
^
∂
w
3
Q
i
=
(
-
Y
i
X
i
0
)
and where T is a translation parameter; R is a rotation parameter; P i =(X i ,Y i ,Z i ) and Q i =(X i ,Y i ,Z i ) are three dimensional position vectors; and k is the number of the rotation parameter where kε1, 2, 3.
9. The method of claim 2 wherein said rotation and translation are determined using a closed-form solution.
10. The method of claim 2 further comprising:
after said step of determining, refining the alignment of said first vector with said second vector.
11. The method of claim 10 wherein said step of refining comprises minimizing a sum of individual distances between points in said first plurality of points and points in said second plurality of points.
12. The method of claim 11 wherein said step of minimizing is performed according to the equation:
E
=
∑
i
=
1
N
E
i
where
E
i
=
arg
min
m
∈
M
m
-
p
i
(
R
,
T
)
-
p
i
(
R
,
T
)
2
and where P is a point cloud representation of a first ear impression, with p i εP; M is a point cloud representation of a second ear impression, with mεM; E i is the squared individual distance between corresponding points in set P and set M; T is a translation parameter; and R is a rotation parameter.
13. An apparatus for registering a first graphical representation of a first ear impression with a second graphical representation of a second ear impression, said apparatus comprising:
means for identifying an aperture of said first ear impression;
means for generating a first vector representing an orientation and a shape of said aperture in said first ear impression; and
means for determining a translation and a rotation of said first vector to achieve alignment of said first vector with a second vector representing an orientation and a shape of an aperture in said second ear impression.
14. The apparatus of claim 13 wherein said first graphical representation comprises a first plurality of points located on a surface of said first ear impression and said second graphical representation comprises a second plurality of points located on a surface of said second ear impression.
15. The apparatus of claim 13 wherein said first vector representing an orientation and a shape of said aperture in said first ear impression comprises a plurality of aperture points along an aperture contour line, an aperture center point, and center points of one or more canal contour lines above the aperture contour line in said first ear impression.
16. The apparatus of claim 15 wherein said second vector representing an orientation and a shape of an aperture in said second ear impression comprises a plurality of aperture points along an aperture contour line, an aperture center point, and center points of one or more canal contour lines above the aperture contour line in said second ear impression.
17. The apparatus of claim 14 further comprising:
means for removing a portion of points from said first plurality of points.
18. The apparatus of claim 17 wherein said portion of points comprises points that are not associated with said aperture of said first ear impression.
19. The apparatus of claim 14 further comprising:
means for refining the alignment of said first vector with said second vector.
20. The apparatus of claim 19 wherein said means for refining the alignment comprises:
means for refining the alignment using a closed-form solution.
21. The apparatus of claim 19 wherein said means for refining comprises means for minimizing a sum of individual distances between points in said first plurality of points and points in said second plurality of points.
22. A non-transitory computer readable medium comprising computer program instructions which, when executed by a processor, define steps for registering a first graphical representation of a first ear impression with a second graphical representation of a second ear impression, said steps comprising:
identifying an aperture of said first ear impression
generating a first vector representing an orientation and a shape of said aperture in said first ear impression; and
determining a translation and a rotation of said first vector to achieve alignment of said first vector with a second vector representing an orientation and a shape of an aperture in said second ear impression.
23. The computer readable medium of claim 22 wherein said first graphical representation comprises a first plurality of points located on a surface of said first ear impression and said second graphical representation comprises a second plurality of points located on a surface of said second ear impression.
24. The computer readable medium of claim 22 wherein said first vector representing an orientation and a shape of said aperture in said first ear impression comprises a plurality of aperture points along an aperture contour line, an aperture center point, and center points of one or more canal contour lines above the aperture contour line in said first ear impression.
25. The computer readable medium of claim 24 wherein said second vector representing an orientation and a shape of an aperture in said second ear impression comprises a plurality of aperture points along an aperture contour line, an aperture center point, and center points of one or more canal contour lines above the aperture contour line in said second ear impression.
26. The computer readable medium of claim 23 further comprising computer program instructions which, when executed by a processor, define the step of:
removing a portion of points from said first plurality of points prior to said step of generating a first vector.
27. The computer readable medium of claim 26 wherein said portion of points comprises points that are not associated with said aperture of said first ear impression.
28. The computer readable medium of claim 23 further comprising computer program instructions which, when executed by a processor, define the step of:
after said step of determining, refining the alignment of said first vector with said second vector are determined using a closed-form solution.
29. The computer readable medium of claim 23 further comprising computer program instructions which, when executed by a processor, define the step of:
after said step of determining, refining the alignment of said first vector with said second vector.
30. The computer readable medium of claim 29 wherein said computer program instructions defining the step of refining comprise computer program instructions defining the step of minimizing a sum of individual distances between points in said first plurality of points and points in said second plurality of points.