Mercator map centered on the reference point

Q&A
4

Thanks @Alpiner for the suggestion it works. Before your suggestion i try to use this crude implementation to get min and max by coordinates:

xMin="$(bc <<<"$myEQLong - $varIncrement")"
xMax="$(bc <<<"$myEQLong + $varIncrement")"
yMin="$(bc <<<"$myEQLat - $varIncrement")"
yMax="$(bc <<<"$myEQLat + $varIncrement")"