Geoida Help

Switching grid/geographic display mode

Question: When I repeatedly switch the display between geographic and grid coords, the picture gradually gets smaller in size.

Answer: With geographic display, only at the equator are the scales in the east-west and north-south directions approximately the same but they become progressively different with increase of distance away from the equator. For example, at the equator one second of longitude is about the same as one second of latitude, i.e., about 30 metres, but it is only about 5 metres at 80 degrees north or south. On switching from geographic to grid mode, the coordinates of the window corners are converted back to grid; on the next swap of coordinate type, the previous (converted) window corners do not quite fit the ratio of the width and height of the display window, so are adjusted to match (values are recorded), thus the window gradually changes in size.