Determination of a position code

• US 6,548,768 B1
• Filed: 10/02/2000
• Issued: 04/15/2003
• Est. Priority Date: 10/01/1999
• Status: Expired due to Term

• Current Assignee: Anoto Group AB
• Original Assignee: Anoto Group AB
• Inventors: Edso, Tomas, Pettersson, Mats Petter
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): NGUYEN, FRANCIS N
• Application Number:
  US09/676,892
• Time in Patent Office: 925 Days
• Field of Search: 345/179, 345/467, 178/18.01, 178/18.03, 178/18.09, 178/19.01, 178/1
• US Class Current: 178/18.01
• 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 19/06018 one-dimensional coding
• CPC Class Codes: G06K 19/06037 multi-dimensional coding
• CPC Class Codes: G06K 7/10722 Photodetector array or CCD scanning
• CPC Class Codes: G06K 7/14 using light without selection of wavelength, e.g. sensing reflected white light G06K7/10831 - G06K7/1097 take precedence
• CPC Class Codes: G06K 7/1417 2D bar codes
• CPC Class Codes: G06K 7/1443 locating of the code in an image
• CPC Class Codes: G06K 7/1456 determining the orientation of the optical code with respect to the reader and correcting therefore
• CPC Class Codes: G06V 10/17 using hand-held instruments
• CPC Class Codes: G06V 10/19 by sensing codes defining pattern positions

Abstract

A method and a device for determining a virtual raster of a code pattern consisting of a plurality of marks with associated coordinates m_n. Each mark is located at a nominal position but displaced from the nominal position in one of a plurality of directions, depending upon the value of the mark. The nominal positions form raster points g_n of the virtual raster, and the raster points are situated on raster lines, which intersect at a first angle. In addition there is a device for determining an initial vector V_1,2 on the basis of the coordinates m₁, m₂ of one or more marks, which initial vector extends approximately between a first and a second adjacent raster point g₁, g₂. A calculation device determines a second vector V_2,3, which forms said angle with the first vector and is the same length as the first vector and extends from the second raster point g₂ approximately to a third raster point g₃. The mark coordinate m₃ which is associated with the third raster point g₃ is determined. Subsequently the actual coordinates are calculated for the third raster point on the basis of the third mark'"'"'s coordinates and its value. The actual coordinates for the third raster point are stored, after which the procedure is repeated taking the second vector as the starting point.

Claims

1. A method for determining a virtual raster of a code pattern consisting of a plurality of marks with associated coordinates m_n, each mark being located at a nominal position but displaced from the nominal position in one of a plurality of directions, depending upon the value of the mark, in addition to which the nominal positions define raster points g_n of the virtual raster, and the raster points are situated on raster lines which intersect at a first angle,

comprising:

determining an initial vector V_1,2 on the basis of the coordinates m₁, m₂ of one or more marks, which initial vector extends approximately between a first and a second adjacent raster point g₁, g₂;

determining a second vector V_2,3 which forms said angle with the first vector and is the same length as the first vector and extends from the second raster point g₂ approximately to a third raster point g₃;

determining a mark coordinate m₃ which belongs to the third raster point g₃;

determining the actual coordinates for the third raster point on the basis of the third mark'"'"'s coordinates and its value and the preceding raster point'"'"'s coordinate; and

storing the third raster point'"'"'s actual coordinates.

2. A method according to claim 1, wherein the initial vector is determined as the vector which connects the two marks which are at a distance which is the least of a set of marks, the vector being extended on each side by a distance corresponding to the displacement of the marks from the associated raster point.

3. A method according to claim 1, wherein the raster points form an essentially orthogonal square grid.

4. A method according to claim 3, wherein each mark is displaced along a raster line by a distance corresponding to between ⅛

and ¼

, preferably ⅙

, of the distance between two raster points.

5. A method according to claim 4, wherein the mark'"'"'s coordinates are determined as the center of gravity of the whole mark.

6. A method according to claim 5, wherein the mark is obtained as an image on a sensor, which has a plurality of pixels, each mark taking up more than one pixel on the sensor surface.

13. A computer-readable computer program product which comprises a computer program with instructions to cause the computer to implement a method according to any one of claims 1-6.

14. A method according to any one of claims 3-6, wherein the initial vector is determined as the vector which connects the two marks which are at a distance which is the least of a set of marks, the vector being extended on each side by a distance corresponding to the displacement of the marks from the associated raster point.

7. A device for determining a virtual raster of a code pattern consisting of a plurality of marks with associated coordinates m_n, each mark being located at a nominal position but displaced from the nominal position in one of a plurality of directions, depending upon the value of the mark, in addition to which the nominal positions define raster points g_n of the virtual raster, and the raster points are situated on raster lines which intersect at a first angle,

comprising

a device for determination of an initial vector V_1,2 on the basis of the coordinates m₁, m₂, of one or more marks, which initial vectors extend approximately between a first and a second adjacent raster point g₁, g₂;

a calculation device for the determining a second vector V_2,3 which forms said angle with the first vector and is the same length as the first vector and extends from the second raster point g₂ approximately to a third raster point g₃;

a calculation device for determining a mark coordinate m₃ which is associated with the third raster point g₃;

a calculation device for determining the actual coordinates of the third raster point on the basis of the third mark'"'"'s coordinates and its value;

a storage device for storing the third raster point'"'"'s actual coordinates; and

a calculation device for calculating the subsequent vector by using. the second vector.

8. A device according to claim 7, wherein the initial vector consists of the vector which connects the two marks which are the least distance apart of a set of marks, the initial vector being extended on both sides by a distance corresponding to the displacement of the marks from the associated raster point.

9. A device according to claim 7, wherein the raster points form an essentially orthogonal square grid.

10. A device according to claim 9, wherein each mark is displaced along a raster line by a distance corresponding to between ⅛

and ¼

, preferably ⅙

, of the distance between two raster points.

11. A device according to claim 10, wherein the coordinates of the mark are determined as the center of gravity of the whole mark.

12. A device according to claim 11, wherein the marks constitute an image on a sensor, which has a plurality of pixels, each mark taking up more than one pixel on the sensor surface.

15. A device according to any one of claims 9-12, wherein the initial vector consists of the vector which connects the two marks which are the least distance apart of a set of marks, the initial vector being extended on both sides by a distance corresponding to the displacement of the marks from the associated raster point.