GB2313729A

GB2313729A - A method for automatically verifying the accuracy of an electronic map

Info

Publication number: GB2313729A
Application number: GB9710775A
Authority: GB
Inventors: Sung Ryong Kim; Young Man Kim; Song Hoon Baik; Hyo Sil Kim; Jae Woo Jeong
Original assignee: KT Corp
Current assignee: KT Corp
Priority date: 1996-05-27
Filing date: 1997-05-23
Publication date: 1997-12-03
Anticipated expiration: 2017-05-23
Also published as: GB2313729B; GB9710775D0; KR970076246A; KR100209350B1

Abstract

A method for automatically verifying the accuracy of an electronic map, said method involving an XORing operation for raster data produced by scanning an original map and vector data finally produced based on the raster data, and a filtering operation for data resulting from the XORing operation. The method includes the steps of scanning an original map, thereby producing raster data, digitizing the raster data, thereby producing vector data, transforming the vector data into raster data, comparing the raster data transformed from the vector data with the original raster data by use of a function of similarity involving an exclusive ORing operation, and removing noise existing in the original raster data by a filtering operation. In accordance with this method, it is possible to reduce the verification time and costs while improving the accuracy of the verification.

Description

METHOD FOR VERIFYING ACCURACY OF A ELECTRONIC MAP USING THE FUNCTION OF SIMILARITY BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method for verifying the accuracy of an electronic map established in a geographic information system, and more particularly to a method for automatically verifying the accuracy of such an electronic map by a comparison between original raster data obtained after scanning an original map and raster data invertedly transformed from vector data produced based on the original raster data.

Description of the Prior Art The electronic map is well known and is produced by scanning an original map previously prepared, thereby obtaining raster data about the original map, and then digitizing straight-line components of the raster data, thereby obtaining vector data. For such an electronic map produced in accordance with the above procedure, it is essential to verify whether or not the electronic map sufficiently reflects information included in raster data.

Such verification between the original map and the electronic map has been accomplished by observing those two data through the naked eye of the verifier, thereby comparing those two data with each other. However, this verification method is problematic in that it requires a lengthened verification time and increased costs while having low accuracy. In order to solve such problems, the present invention provides an automatic verification method. In accordance with this automatic verification method, vector data is transformed into raster data which is, in turn, exclusively ORed (XORed) with original raster data. In accordance with such an operation, it is possible to easily find different data portions between the raster data produced by scanning the original map and the vector data finally produced based on the raster data. In accordance with the XORing operation, a value of 0 is outputted when operation codes have the same value. When operation codes have different values, a value of 1 is outputted.

SUMMARY OF THE INVENTION An objective of the invention is to provide a method for automatically verifying the accuracy of an electronic map, said method involving the steps of XORing raster data transformed from vector data with original raster data of an original map, and filtering the resultant data, thereby solving the problem involved in the electronic map verification using a visual test.

In accordance with the present invention, this objective is accomplished by providing a method for automatically verifying the accuracy of an electronic map, comprising the steps of: scanning an original map, thereby producing raster data; digitizing the raster data, thereby producing vector data; transforming the vector data into raster data; comparing the raster data transformed from the vector data with the original raster data by use of a function of similarity involving an exclusive ORing operation; and removing noise existing in the original raster data by a filtering operation.

BRIEF DESCRIPTION OF THE DRAWINGS Other objectives and aspects of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings in which: FIG. la is a schematic view illustrating original raster data obtained after scanning an original map; FIG. ib is a schematic view illustrating raster data transformed from vector data which is produced based on the original raster data; FIG. 2 is an enlarged view illustrating line components of the original raster data; FIG. 3 is a schematic view illustrating the result obtained after an XORing operation for original raster data and raster data transformed from vector data; FIG. 4 is a schematic view illustrating the result obtained after removing noise from data resulting from the XORing operation; and FIG. 5 is a flow chart illustrating sequential steps of the electronic map verifying method according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the present invention, an automatic verification for the accuracy of an electronic map is carried out using the function of similarity. The function of similarity is adapted to measure the similarity between the original raster data R1 of an original map and raster data R2 transformed from vector data produced based on the original raster data Ri. Such a function of similarity, fm should satisfy the following condition: fm (R1, R2) = 0 " R1 = R2 That is, where raster data R1 and R2 are identical to each other, the function of similarity has a value of "0". In other words, when the function of similarity has a value of "0", raster data R1 and R2 are identical to each other. By virtue of such a characteristic, the XORing operation can be used to operate the function of similarity between raster data.

When it is assumed that "Oj" represents original raster data, "Vj" represents vector data produced based on the original raster data, fr" represents a function for transforming the vector data into raster data, and "s" represents an XORing operation, the XORing operation between the original raster data and the vector data transformed into raster data is expressed as follows: I = Oi e fr(V1.) where, "fr(Vi)" represents raster data transformed from the vector data Vj.

When all data values of the XORing operation result I correspond to "0", both the original raster data and vector data are considered to be identical to each other. When the XORing operation result I has a data value other than "0", the original raster data and vector data are different from each other.

FIG. la illustrates original raster data obtained after scanning an original map whereas FIG. ib illustrates raster data transformed from vector data which is produced based on the original raster data.

FIG. 2 is an enlarged view of the original raster data. FIG.

2, indicates that the original raster data contains noise. Where raster data is produced based on an original map, it may have a lot of noise resulting from a distortion phenomenon occurring during the scanning operation for the original map, in addition to noise existing in the original map. This noise is different from an error generated in the process of producing vector data.

Accordingly, such noise should be eliminated. Typically, this noise has a size smaller than the actual data. Accordingly, it is possible to remove noise by a filtering operation.

FIG. 3 illustrates the result obtained after an XORing operation for two data is carried out to derive the similarity of those two data. Most of groups of pixels indicated in FIG. 3 are noise existing in original raster data whereas the remaining straight lines are different portions of original raster data and vector data transformed into raster data. Where an XORing operation is carried out for such raster data and vector data, a number of pixels appear due to the difference between those data resulting from noise existing in the original raster data.

In order to achieve an accurate verification, it is desirable to compare the raster data and vector data after filtering the above-mentioned noise. The filtering operation involves the first step of scanning data obtained after the XORing operation from the upper left end portion of the data, thereby finding pixels having a value of "1", the second step of finding groups of pixels neighboring one another in four or eight directions, calculating the width Wj and height H. of a minimum-size block including each pixel group, and converting the pixel value of pixel groups into a value of 0, when the size of the greater of Wj, Hj is equal to or smaller than a predetermined filter size Eo (max(Wj, H.) s FIG. 4 is the result obtained after removing noise from data resulting from an XORing operation carried out for original raster data Oi of FIG. 1 and raster data transformed from vector data Vj by use of an filtering operation in which groups of pixels neighboring one another in four directions are filtered using a filter having a desired filter size eO. By referring to the result of FIG. 4, it is possible to discover the amount of different data.

Thus, it is possible to verify the accuracy of the electronic map.

FIG. 5 is a flow chart illustrating sequential steps of the electronic map verifying method according to the present invention.

In accordance with the method of the present invention, raster data is first produced by scanning an electronic map (Step 50). The raster data is then digitized (Step 51), thereby producing vector data (Step 52). In order to carry out an XORing operation for the vector data with the raster data, the vector data is then transformed into raster data (Step 53). Thereafter, an XORing operation is carried out for the raster data transformed from the vector data and the original raster data (Step 54). A filtering operation is then carried out to remove noise from data obtained after the XORing operation (Step 55). Finally, different data portions between the two raster data are found (Step 56). Thus, the accuracy of the electronic map is verified.

As is apparent from the above description, the present invention provides a method for automatically verifying the accuracy of an electronic map, said method involving an XORing operation for raster data produced by scanning an original map and vector data finally produced based on the raster data, and a filtering operation for data resulting from the XORing operation.

Accordingly, it is possible to reduce the verification time and costs while improving the accuracy of the verification.

Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

WHAT IS CLAIMED IS:

1. A method for automatically verifying the accuracy of an electronic map, comprising the steps of: scanning an original map, thereby producing raster data; digitizing the raster data, thereby producing vector data; transforming the vector data into raster data; comparing the raster data transformed from the vector data with the original raster data by use of a function of similarity involving an exclusive ORing operation; and removing noise existing in the original raster data by a filtering operation.