How to check if three coordinates form a line Assume I have three coordinates from a world map in Longitude + Latitude. Is there a way to determine these three coordinates form a straight line?
What if I was using a system with bounds that defines the 2 corners (northeast - southwest) in Long/Lat?
The long & lat are expressed in decimal degrees.

If a point has longitude $\alpha$ (from $-180^\circ$ to $+180^°$) and latitude $\beta$ (from $-90^°$ to $+90^°$), the corresponding 3D point is 
$$ (x,y,z)=(\cos\alpha\cos\beta,\sin\alpha\cos\beta,\sin\beta).$$
If you have three such points, the determinant
$$ \left|\begin{matrix}x_1&x_2&x_3\\y_1&y_2&y_3\\z_1&z_2&z_3\end{matrix}\right|$$
is zero if and only if the plane through the three points passes through the Earth center.
In the presence of rounding errors aou will never have exactly zero, so the question is when to accept an almost zero value as good ...
A simplified alternative: If all your points are relatively close to one another (e.g. less than 100km apart and not too close to the poles), it is a not-too-bad approximation to work with the angles themselves (after all viewing the Earth as a sphere is also just an approximation) as $x$ and $y$ coordinates and check collinearity, that is
$$ \left|\begin{matrix}\alpha_1&\alpha_2&\alpha_3\\\beta_1&\beta_2&\beta_3\\1&1&1\end{matrix}\right|\approx 0.$$
