I have a GPS point:
I want to know what the GPS point is exactly 3 miles east and west of this point.
I've use the formulae to work out the northern position (in PHP):
$lat = 51.747724;
$lng = -0.406958;
$radius_metres = ceil(3 * 1609.344);
$top_lat = $lat + $radius_metres/111111*(cos(10 * pi() / 180));
$north_lat = $top_lat;
$north_lng = $lng;
$left_lng = $lng - $radius_metres/111111*(cos(10 * pi() / 180));
$east = array($lat,$left_lng);
$right_lng = $lng + $radius_metres/111111*(cos(10 * pi() / 180));
$west = array($lat,$right_lng);
However, when I use an as-the-crow-files formula, the point is approximately 1.8 miles away
(and not 3 miles)
What is the best way of working out the east and west points.
The maximum distance between my GPS coordinate and these points will be 20 miles (so not a lot).