Method and device for decoding a position-coding pattern

• US 20030128194A1
• Filed: 10/29/2002
• Published: 07/10/2003
• Est. Priority Date: 10/29/2001
• Status: Active Grant

• Current Assignee: Anoto Group AB
• Original Assignee: Anoto Group AB
• Inventors: Pettersson, Mats Petter
• Granted Patent: US 7,145,556 B2
• Time in Patent Office: Days
• US Class Current: 345/173
• CPC Class Codes: G06F 3/0321 by optically sensing the absolute position with respect to a regularly patterned surface forming a passive digitiser, e.g. pen optically detecting position indicative tags printed on a paper sheet constructional details of pen-shaped pointing devices G06F3/03545, G06F3/03542, G06F3/037
• CPC Class Codes: G06F 3/03545 Pens or stylus
• CPC Class Codes: G06K 19/06037 multi-dimensional coding
• CPC Class Codes: G06K 7/1443 locating of the code in an image
• CPC Class Codes: G06V 10/17 using hand-held instruments
• CPC Class Codes: G06V 10/19 by sensing codes defining pattern positions

Abstract

In a method for position decoding, a position is calculated on the basis of information determined from a partial area, imaged by a sensor, of a position-coding pattern. If the position calculation fails, the information from the partial area recorded by the sensor is matched with information about how the position-coding pattern is designed in a plurality of matching partial areas, which each define a position in the position-coding pattern. The position of the positions defined by the matching partial areas, which according to the matching step is the most probable position in the position-coding pattern for the imaged partial area is accepted as the decoded position.

A device and a computer program for carrying out the method are also described.

Claims

1. A method for position decoding, comprising the step of

calculating a position on the basis of information determined from a partial area, imaged by a sensor, of a position-coding pattern;

characterized by the steps of

if the calculation of the position fails, matching the information from the partial area imaged by the sensor with information about how the position-coding pattern is designed in a plurality of matching partial areas which each define a position in the position-coding pattern, and

accepting the position of the positions defined by the matching partial areas which according to the matching step is the most probable position in the position-coding pattern for the imaged partial area.

2. A method as claimed in claim 1, wherein the matching is carried out in a matching area adjacent to a previously accepted position.

3. A method as claimed in claim 1 or 2, wherein the matching is carried out in one dimension at a time in the position-coding pattern.

4. A method as claimed in claim 1, 2 or 3, wherein the position-coding pattern codes each position by means of a plurality of elements which can each assume at least two different values, and wherein the matching step comprising the substeps of

determining which values are assumed by each of the elements of the matching partial areas;

and

for each matching partial area and on the basis of the information from the imaged subset of the position-coding pattern, determining a measure of the probability that the elements of the imaged partial area assume the same values as the elements of the matching partial area.

5. A method as claimed in claim 4, wherein the information from the imaged partial area comprises a set of probability values which each indicate a probability that one of the elements of the imaged partial area assumes one of the possible values, and wherein the measure of the probability is determined on the basis of the probability values for the values assumed by the elements of the matching partial area.

6. A method as claimed in claim 4, wherein the measure of the probability is determined on the basis of the number of elements in the imaged partial area which assume the same value as the corresponding elements in the matching partial area.

7. A method as claimed in any one of claims 4-6, wherein each position in the position-coding pattern is coded by a matrix of symbols, where each symbol constitutes an element.

8. A method as claimed in any one of claims 4-6, wherein each position in the position-coding pattern is coded by a matrix of symbols which are divided into a plurality of groups, and wherein each group constitutes an element.

9. A method as claimed in any one of claims 4-6, wherein each position is coded by a matrix of symbols, which are divided into a plurality of groups, and wherein each of said elements is defined by at least two groups of symbols.

10. A method as claimed in any one of claims 7-9, wherein each symbol comprises a mark which is displaced in one of four predetermined directions from a nominal position in the position-coding pattern.

11. A method as claimed in claim 8 or 9, wherein the values of the symbols in a group correspond to a partial sequence in a cyclic number sequence, which has the property that each partial sequence of a predetermined length has an unambiguously determined place in the number sequence.

12. A method as claimed claim 9, wherein the values of the symbols in a group form a partial sequence in a cyclic number sequence, which has the property that each partial sequence of a predetermined length has an unambiguously determined place in the number sequence, and wherein the elements which are defined in pairs by the groups consist of the differences between the places of the groups in the number sequence.

13. A method as claimed in any one of the preceding claims, further comprising the step of verifying the position accepted on the basis of the imaged partial area by means of the information from the imaged partial area.

14. A method as claimed in any one of the preceding claims, wherein each position in the position-coding pattern is coded by means of a plurality of position numbers, which in pairs define a plurality of difference numbers determining the position;

wherein the information about how the position-coding pattern is made up consists of said difference numbers and the information from the imaged partial area comprises position numbers which are determined from the partial area; and

wherein the matching comprises determining how many of the position numbers determined from the imaged partial area correspond with each other as regards the difference numbers.

15. A computer program which comprises program code which, when executed in a computer, causes the computer to carry out a method according to any one of claims 1-14.

16. A computer-readable storage medium on which is stored a computer program which, when executed in a computer, causes the computer to carry out a method according to any one of claims 1-14.

17. A device for position decoding, said device comprising a signal-processing unit, which is adapted to calculate a position on the basis of information determined from a partial area, imaged by a sensor, of a position-coding pattern;

characterized in that the signal-processing unit is further adapted to match, if the calculation of the position fails, the information from the partial area imaged by the sensor with information about how the position-coding pattern is designed in a plurality of matching partial areas, which each define a position in the position-coding pattern, and to accept the position of the positions defined by the matching partial areas, which according to the matching step is the most probable position in the position-coding pattern for the imaged partial area.