Increasing accuracy of discrete curve transform estimates for curve matching

• US 7,327,887 B2
• Filed: 05/06/2003
• Issued: 02/05/2008
• Est. Priority Date: 04/10/2002
• Status: Active Grant

• Current Assignee: National Instruments Corporation (Emerson Electric Company)
• Original Assignee: National Instruments Corporation (Emerson Electric Company)
• Inventors: Wenzel, Lothar
• Primary Examiner(s): Mehta; Bhavesh M
• Assistant Examiner(s): SCHAFFER, JONATHAN C
• Application Number:
  US10/430,546
• Publication Number:
  US 20030194135A1
• Time in Patent Office: 1,736 Days
• Field of Search: 382/209, 382/289, 382/290, 382/296, 382/297
• US Class Current: 382/209
• CPC Class Codes: G06V 10/32 Normalisation of the pattern dimensions
• CPC Class Codes: G06V 10/46 Descriptors for shape, contour or point-related descriptors, e.g. scale invariant feature transform [SIFT] or bags of words [BoW]; Salient regional features colour feature extraction G06V10/56
• CPC Class Codes: G06V 10/471 using approximation functions
• CPC Class Codes: G06V 10/7515 Shifting the patterns to accommodate for positional errors
• CPC Class Codes: G06V 10/752 Contour matching

Abstract

System and method for estimating a rotational shift between a first discrete curve and a second discrete curve, where the second discrete curve is a rotationally shifted version of the first discrete curve. First and second discrete curves are received. A rotational shift between the first discrete curve and the second discrete curve is estimated based on the first discrete curve and the second discrete curve. A cumulative rotational shift is updated based on the estimated rotational shift. A rotationally shifted version of the second discrete curve is generated based on the cumulative rotational shift. The estimating, updating, and generating are performed in an iterative manner using the respective rotationally shifted discrete curve for each iteration until a stopping condition occurs, thereby determining a final estimate of the rotational shift between the first discrete curve and the second discrete curve. The final estimate may be used to perform curve matching.

Claims

1. A computer-accessible memory medium which stores program instructions for estimating a rotational shift between a first discrete curve and a second discrete curve, wherein the program instructions are executable to perform:

receiving a first discrete curve and a second discrete curve, wherein the second discrete curve is a rotationally shifted version of the first discrete curve, wherein the first discrete curve and the second discrete curve each comprises a respective 2D discrete curve, and wherein the first discrete curve and the second discrete curve each comprises a respective sequence of points in the complex plane;

estimating a rotational shift between the first discrete curve and the second discrete curve based on the first discrete curve and the second discrete curve, wherein said estimating the rotational shift between the first discrete curve and the second discrete curve based on the first discrete curve and the second discrete curve comprises calculating;

$\mathrm{\alpha <br><br>}=\frac{<br><br><br><br>e<br><br>\left(\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br>\left(z_n-y_n\right)<br><br>{\left(y_{n+1}-y_n\right)}^{*}\right)}{\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br>{<br><br>\left(y_{n+1}-y_n\right)<br><br>}^2},$

wherein y_n and z_n refer to points in the first discrete curve and the second discrete curve, respectively;

updating a cumulative rotational shift based on the estimated rotational shift;

generating a rotationally shifted version of the second discrete curve based on the cumulative rotational shift;

performing said estimating, said updating, and said generating in an iterative manner using the respective rotationally shifted discrete curve for each iteration until a stopping condition occurs, thereby determining a final estimate of the rotational shift between the first discrete curve and the second discrete curve, and

storing the final estimate of the rotational shift, wherein the final estimate of the rotational shift is useable to perform discrete curve matching.

2. The memory medium of claim 1, wherein the stopping condition occurs when a magnitude of the estimated rotational shift is less than a specified threshold value.

3. The memory medium of claim 1, wherein the stopping condition occurs when a specified number of iterations have elapsed.

4. The memory medium of claim 1, wherein the first discrete curve and the second discrete curve comprise substantially smooth discrete curves.

5. The memory medium of claim 1, wherein the first discrete curve and the second discrete curve each comprise a respective closed curve.

6. The memory medium of claim 1,

wherein the first discrete curve and the second discrete curve each comprises the same number of points, wherein for each curve, each point corresponds to a value of an index;

and

wherein the value of the estimated rotational shift is normalized with respect to the index.

7. The memory medium of claim 6,

wherein an estimated a rotational shift value of 1 corresponds to a cyclic shift of one point in the second discrete curve.

8. The memory medium of claim 1, wherein the second discrete curve is rotationally shifted from the first discrete curve by less than a rotational distance between successive points in the second discrete curve.

9. The memory medium of claim 1, wherein the second discrete curve is rotationally shifted from the first discrete curve by less than or equal to 5 degrees.

10. The memory medium of claim 1, wherein the second discrete curve is rotationally shifted from the first discrete curve by less than or equal to 1 degree.

11. The memory medium of claim 1, wherein said rotational shifting the second discrete curve based on the estimated rotational shift to generate a respective rotationally shifted discrete curve further comprises:

interpolating the second discrete curve.

12. The memory medium of claim 1, wherein the program instructions are further executable to perform:

outputting the final estimate of the rotational shift between the first discrete curve and the second discrete curve.

13. The memory medium of claim 1, wherein the program instructions are further executable to perform:

performing curve matching on the first discrete curve and the second discrete curve using the final estimate of the rotational shift, thereby generating results indicating a degree of match between the first discrete curve and the second discrete curve.

14. A method for estimating a rotational shifi between a first discrete curve and a second discrete curve, the method comprising:

receiving a first discrete curve and a second discrete curve, wherein the second discrete curve is a rotationally shifted version of the first discrete curve, wherein the first discrete curve and the second discrete curve each comprises a respective 2D discrete curve, and wherein the first discrete curve and the second discrete curve each comprises a respective sequence of points in the complex plane;

estimating a rotational shift between the first discrete curve and the second discrete curve based on the first discrete curve and the second discrete curve, wherein said estimating the rotational shift between the first discrete curve and the second discrete curve based on the first discrete curve and the second discrete curve comprises calculating;

$\mathrm{\alpha <br><br>}=\frac{<br><br><br><br>e<br><br>\left(\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br>\left(z_n-y_n\right)<br><br>{\left(y_{n+1}-y_n\right)}^{*}\right)}{\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br>{<br><br>\left(y_{n+1}-y_n\right)<br><br>}^2},$

wherein y_n and z_n refer to points in the first discrete curve and the second discrete curve, respectively;

updating a cumulative rotational shift based on the estimated rotational shift;

generating a rotationally shifted version of the second discrete curve based on the cumulative rotational shift; and

performing said estimating, said updating, and said generating in an iterative manner using the respective rotationally shifted discrete curve for each iteration until a stopping condition occurs, thereby determining a final estimate of the rotational shift between the first discrete curve and the second discrete curve; and

storing the final estimate of the rotational shift, wherein the final estimate of the rotational shift is useable to perform discrete curve matching.

15. A system for estimating a rotational shift between a first discrete curve and a second discrete curve, the system comprising:

a processor;

a memory medium coupled to the processor;

an input coupled to the processor and the memory medium; and

an output coupled to the processor and the memory medium;

wherein the input is operable to receive a first discrete curve and a second discrete curve, wherein the second discrete curve is a rotationally shifted version of the first discrete curve, wherein the first discrete curve and the second discrete curve each comprises a respective 2D discrete curve, and wherein the first discrete curve and the second discrete curve each comprises a respective sequence of points in the complex plane;

wherein the memory medium stores program instructions which are executable by the processor to;

estimate a rotational shift between the first discrete curve and the second discrete curve based on the first discrete curve and the second discrete curve, wherein said estimating the rotational shift between the first discrete curve and the second discrete curve based on the first discrete curve and the second discrete curve comprises calculating;

$\mathrm{\alpha <br><br>}=\frac{<br><br>e<br><br>\left(\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br><br><br>\left(z_n-y_n\right)<br><br>{\left(y_{n-1}-y_n\right)}^{*}\right)}{\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br><br><br>{<br><br>\left(y_{n+1}-y_n\right)<br><br>}^2},$

wherein y_n and z_n refer to points in the first discrete curve and the second discrete curve, respectively;

update a cumulative rotational shift based on the estimated rotational shift;

generate a rotationally shifted version of the second discrete curve based on the cumulative rotational shift; and

perform said estimating, said updating, and said generating in an iterative manner using the respective rotationally shifted discrete curve for each iteration until a stopping condition occurs, thereby determining a final estimate of the rotational shift between the first discrete curve and the second discrete curve;

wherein the output is operable to output the final estimate of the rotational shift between the first discrete curve and the second discrete curve, and wherein the final estimate of the rotational shift is useable to perform discrete curve matching.

16. A system for estimating a rotational shift between a first discrete curve and a second discrete curve, the system comprising:

means for receiving a first discrete curve and a second discrete curve, wherein the second discrete curve is a rotationally shifted version of the first discrete curve, wherein the first discrete curve and the second discrete curve each comprises a respective 2D discrete curve, and wherein the first discrete curve and the second discrete curve each comprises a respective sequence of points in the complex plane;

means for estimating a rotational shift between the first discrete curve and the second discrete curve based on the first discrete curve and the second discrete curve, wherein said estimating the rotational shift between the first discrete curve and the second discrete curve based on the first discrete curve and the second discrete curve comprises calculating;

$\mathrm{\alpha <br><br>}=\frac{<br><br>e<br><br>\left(\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br><br><br>\left(z_n-y_n\right)<br><br>{\left(y_{n-1}-y_n\right)}^{*}\right)}{\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br><br><br>{<br><br>\left(y_{n+1}-y_n\right)<br><br>}^2},$

wherein y_n and z_n refer to points in the first discrete curve and the second discrete curve, respectively;

means for updating a cumulative rotational shift based on the estimated rotational shift;

means for generating a rotationally shifted version of the second discrete curve based on the cumulative rotational shift;

means for performing said estimating, said updating, and said generating in an iterative manner using the respective rotationally shifted discrete curve for each iteration until a stopping condition occurs, thereby determining a final estimate of the rotational shift between the first discrete curve and the second discrete curve; and

means for storing the final estimate of the rotational shift, wherein the final estimate of the rotational shift is useable to perform discrete curve matching.

17. A computer-accessible memory medium which stores program instructions for estimating a rotational shift between a first discrete curve and a second discrete curve, wherein the program instructions are executable to perform:

receiving a first discrete curve and a second discrete curve, wherein the second discrete curve is a rotationally shifted version of the first discrete curve, wherein the first discrete curve and the second discrete curve each comprises a respective 2D discrete curve, and wherein the first discrete curve and the second discrete curve each comprises a respective seciuence of points in the complex plane;

estimating a rotational shift between the first discrete curve and the second discrete curve based on the first discrete curve and the second discrete curve, wherein said estimating the rotational shift between the first discrete curve and the second discrete curve based on the first discrete curve and the second discrete curve comprises calculating;

$\mathrm{\alpha <br><br>}=\frac{<br><br>e<br><br>\left(\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br><br><br>\left(z_n-y_n\right)<br><br>{\left(y_{n-1}-y_n\right)}^{*}\right)}{\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br><br><br>{<br><br>\left(y_{n+1}-y_n\right)<br><br>}^2},$

wherein y_n and z_n refer to points in the first discrete curve and the second discrete curve, respectively;

generating a rotationally shifted version of the second discrete curve based on the cumulative rotational shift;

performing said estimating, and said generating in an iterative manner using the respective rotationally shifted discrete curve for each iteration until a stopping condition occurs, thereby determining a final estimate of the rotational shift between the first discrete curve and the second discrete curve; and

storing the final estimate of the rotational shift, wherein the final estimate of the rotational shift is useable to perform discrete curve matching.

18. A medium which is configurable programmable hardware element configured for estimating a rotational shift between a first discrete curve and a second discrete curve, wherein the programmable hardware element is configured to perform:

receiving a first discrete curve and a second discrete curve, wherein the second discrete curve is a rotationally shifted version of the first discrete curve, wherein the first discrete curve and the second discrete curve each comprises a respective 2D discrete curve, and wherein the first discrete curve and the second discrete curve each comprises a respective sequence of points in the complex plane;

estimating a rotational shift between the first discrete curve and the second discrete curve based on the first discrete curve and the second discrete curve, wherein said estimating the rotational shift between the first discrete curve and the second discrete curve based on the first discrete curve and the second discrete curve comprises calculating;

$\mathrm{\alpha <br><br>}=\frac{<br><br>e<br><br>\left(\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br><br><br>\left(z_n-y_n\right)<br><br>{\left(y_{n-1}-y_n\right)}^{*}\right)}{\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br><br><br>{<br><br>\left(y_{n+1}-y_n\right)<br><br>}^2},$

wherein v_n and z_n refer to points in the first discrete curve and the second discrete curve, respectively;

updating a cumulative rotational shift based on the estimated rotational shift;

generating a rotationally shifted version of the second discrete curve based on the cumulative rotational shift;

performing said estimating, said updating, and said generating in an iterative manner using the respective rotationally shifted discrete curve for each iteration until a stopping condition occurs, thereby determining a final estimate of the rotational shift between the first discrete curve and the second discrete curve; and

storing the final estimate of the rotational shift, wherein the final estimate of the rotational shift is useable to perform discrete curve matching.