Automatic Reading of Altitude Values with Contours on Charts
Nobumichi Ishimura, Kanemichi Kasahara, Ikuo INOUE · The Journal of Japan Institute of Navigation · 1991
To make a big step forward in automatic reading of contours on charts, we need to add the function for recognition of the altitude values with contours to its processing. In this paper, therefore, we propose a method to carry out this function efficiently and verify the validity of this method through the experiment using actual chart data. In this method, the altitude reading is executed by two steps. The first step is to cut off only the region where the altitude values are described on chart images. The second step is the recognition of numerical letters that are cut off in the previous step. Although the recognition processing generally puts much load on a computer using many parameters as the features of letters, this recognition is very simple and useful. The reason is that it can be accomplished by only two parameters. Namely, one is the number of pixels composing the digital line drawings. The other is the average of the magnitude of the directional changes per pixel in the trace on a digital line drawing. These parameters are also essential to the classification of line drawings and can be commonly used in it.