SIGHT REDUCTION USING THE INTERCEPT METHOD

The spreadsheet intercept.xls solves the navigation triangle in accordance with the intercept method of Marcq Saint-Hilaire. Enter the latitude and longitude of the assumed position (AP) in cells A2, B2, the GHA and Declination (GP) in cells C2, D2, and the observed altitude (Ho) in cell E2. Cell F2 computes and displays the Local Hour Angle (LHA). If you have already determined LHA and want to use it as input, enter it in place of GHA (cell C2) and set the AP Longitude (in cell B2) to zero. The calculated altitude (Hc) at the AP is in cells A6, B6, C6 and the intercept distance (in nautical miles) is displayed in cells D6 and E6. The azimuth Zn toward the GP from the assumed position is in cell F6. This allows you to plot the line of position (LOP), along which the “true” position (TP) is located. Rows 7, 9, 12, and 15 contain additional information about LOP properties that allow the plotting of the LOP without the azimuth line using the T-PlotterTM. This reduces the clutter on the chart when multiple LOP’s are plotted.