GB1162316A - Improvements in or relating to Chart Position Indicating Apparatus - Google Patents

Abstract

1,162,316. Indicating apparatus. DECCA Ltd. March 28, 1968 [July 11, 1967], No.31899/67. Heading G1J. Chart position indicating apparatus for use with a radio navigation system adapted to provide, at a mobile receiver, two outputs, M and N, each identifying a position line in a respective one of two families of intersecting position lines, the intersection of the two position lines representing the location of the craft, comprises a chart drawn by assuming the position lines all to be straight, computing, in cartesian co-ordinates with respect to the chart, the co-ordinates of the four intersections a 11 , a 12 , a 21 , a 22 of a pair of position lines M 1 , M 2 in one family with a pair N 1 , N 2 in the other family and plotting the chart so that for any point Z on the chart either position line M (or N) through the point Z divides either selected position line N 1 , N 2 (M 1 , M 2 ) in the other family in the same ratio as the cartesian co-ordinates Xz, Yz of the point Z divide the respective cartesian co-ordinates of the intersections lying on the selected line in the other family; an index 81a relatively movable in the two cartesian co-ordinate directions over the surface of the chart, motors 78, 86 for displacing the index 81a relative to the chart 83 to indicate the chart position (Xz, Yz) of the location of the craft automatically in accordance with two outputs, defining Xz and Yz respectively, of a computer, Fig.4 (not shown), responsive to the navigation system outputs, M, N, the computer being arranged to compute Xz and Yz as the values of expressions in the form k 1 MN + k 2 M + k 3 N + k 4 and k' 1 MN + k' 2 M + k' 3 N + k' 4 wherein k n and k' n for n = 1 to 4 are constants derived from the cartesian co-ordinates of the four intersections a 11 , a 12 , a 21 , a 22 used when the chart was drawn. Each chart may carry marks that can be sensed and which represent the constants associated therewith so that when a chart is in use constants appropriate thereto can be entered automatically in the computer. The apparatus provides a practical solution to the problem of reducing the complexity of the computation required to convert radio navigation data to co-ordinate data suitable for plotting without introducing undue distortion of the chart.