Telegraphy – Systems – Position coordinate determination for writing
Reexamination Certificate
2000-05-26
2003-05-27
Saras, Steven (Department: 2675)
Telegraphy
Systems
Position coordinate determination for writing
C382S306000, C235S494000
Reexamination Certificate
active
06570104
ABSTRACT:
FIELD OF THE INVENTION
The invention also relates to a method of creating a position-coding pattern, use of a position-coding pattern, a device for position determination and storage media storing computer programs for generating and for decoding of the position-coding pattern.
BACKGROUND OF THE INVENTION
In many situations it is desirable to be able to determine an absolute position on a surface, for example in connection with the digitization of drawings or when one wishes to create an electronic version of handwritten information.
U.S. Pat. No. 5,852,434 describes a device for the determination of an absolute position. The device comprises a writing surface provided with a position code by means of which it is possible to determine X- and Y-coordinates, a detector capable of detecting the position code, and a processor capable of determining the position of the detector in relation to the writing surface on the basis of the detected position code.
Three examples of a position code are provided in U.S. Pat. No. 5,852,434. The first example is dots, each of which is made up of three concentric circles. The outermost circle represents the X-coordinate and the middle circle represents the Y-coordinate. Furthermore, the two outermost circles are divided into 16 parts, which depending upon whether they are filled in or not indicate different numbers. This means that each pair of coordinates X, Y is coded with a dot with a specific appearance.
In the second example, the coordinates are indicated in each point on the writing surface with the aid of a barcode, a barcode for the X-coordinate being placed above a barcode for the Y-coordinate.
As a third example, it is stated that a checkerboard pattern can be used for coding the X- and Y-coordinates. However, no explanation is given of how the checkerboard pattern is structured or how it can be translated into coordinates.
One problem associated with the known pattern is that it is made up of complex symbols. The smaller these symbols are the more difficult it is to produce the patterned writing surface and the greater the risk of incorrect position determination. But the larger the symbols, the poorer the position resolution.
A further problem is that the image processing becomes fairly complicated because of the fact that the symbols that must be interpreted are complex.
Yet another problem is that the sensor surface of the device used for recording the symbols must be made large enough to enable it to record four symbols at the same time so that it will definitely record at least one symbol in its entirety, which is necessary in order to carry out the position determination.
WO 92/17859 discloses a device for position determination which comprises a code surface with a pattern which has a so-called windowing pattern. This means that the pattern has the property that for each arbitrary partial surface of the pattern of a predetermined magnitude, the location of the partial surface in the pattern can be determined. The pattern is composed of so-called m-sequences which have the property that each subsequence of the length k appears only once in the sequence.
Appendix A of WO 92/17859 provides the following examples of how the pattern can be composed and how a position can be decoded.
Start from the following m-sequences: s=(0,0,1,0,1,1,1) and t=(0,1,1). Build a position-coding pattern by letting a first column in the pattern equal the sequence s. To build the following columns, look at the t-sequence. If the first element in the t-sequence is 0, the second column consists of the s-sequence. If the first element instead is 1, the second column consists of the s-sequence circularly shifted by one step. The following columns are built in a corresponding manner according to the values of the elements in the t-sequence. The following pattern is then obtained:
0
0
1
1
0
0
0
1
1
1
0
0
0
0
1
0
1
1
0
1
1
1
1
0
1
1
1
1
Now assume that one wants to find the position of a partial surface with the below indicated subset of the pattern.
1
0
0
0
1
0
1
0
1
The first column in the subset is (1,0,1). This sub-sequence appears in position 2 in the s-sequence. The circular shifts in the subset are (1,1). This subsequence appears in position 1 in the t-sequence. The accumulated appears in the pattern are (0,0,1,2) and therefore the vertical position of the subset is 2+0=2. The position of the subset on the partial surface thus is (1,2).
With this pattern, the above described problems are obviated, involving complex symbols and the need for recording four symbols in order to definitely record one symbol in its entirety.
An interesting characteristic of a position-coding pattern of this type, however, is the possibility of coding a large pattern with many unique positions so that position determination can be carried out on a surface which is as large as possible. In the example above, the magnitude is limited in the vertical direction by the length of the s-sequence and the magnitude in the horizontal direction by the length of the t-sequence. The length of these sequences can, however, not be increased infinitely since the sequences should have the characteristic that if one takes a subsequence of k-bits, this subsequence should only appear in one position in the sequence. An increase of the sequence length may thus require an increase of the subsequence length and thus an increase of the partial surface that must be recorded to be able to determine a position.
SUMMARY OF THE INVENTION
It is an object of the present invention to completely or partly obviate this problem.
This object is achieved by a product according to claim
1
, a method of creating a position-coding pattern according to claim
10
, electronic storage media according to claims
14
,
15
and
16
, a device for position determination according to claim
20
and use of a position-coding pattern according to claim
23
.
More specifically, the invention relates to a product for position determination, which product has a surface and a position-coding pattern which extends across the surface and codes a plurality of positions on the surface, each position of a said plurality of positions being coded by a specific part of the position-coding pattern and each such specific part of the position-coding pattern also contributing to the coding of adjacent positions, said position-coding pattern further being based on a first string of symbols which contains a first predetermined number of symbols and which has the characteristic that if one takes a second predetermined number of symbols from the first string of symbols, the location of these symbols in the first string of symbols is unambiguously determined, the first string of symbols being used to determine the position in a first dimension on the surface. Moreover the position-coding pattern contains at least a first row of symbols which are arranged according to the first string of symbols, and at least a second row of symbols which are arranged according to a second string of symbols having the same characteristic as the first string of symbols, a displacement being obtained between the first and the second string of symbols along the first and the second row when the first and the second string of symbols are repeated on them.
By using the displacement between a first and a second string of symbols, it is possible to code a larger number of positions in the direction in which the first and the second string of symbols are used for the coding. If the first string of symbols has the length n and the second string of symbols has the length n−1, it is possible to code, instead of n-positions, n(n−1) positions in the direction in which the first string of symbols is used by utilizing the first displacement or interference obtained between the first and the second in this direction.
It is evident that the position-coding pattern is of the same type, i.e. has the same characteristic as the windowing pattern described by way of introduction.
The term “row” should here be interpreted in a wide sense and not be
Ericson Petter
Hugosson Ola
Anoto AB
Birch & Stewart Kolasch & Birch, LLP
Jorgensen Leland R.
Saras Steven
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