Is a straight line on google earth or google maps geodesic? That is, when I view google earth or google maps data on my 2d computer screen, is the image I am seeing “adjusted” correctly that a straight line on this “adjusted” image is actually geodesic?
If it is not, are there any options that I can choose within these applications which will let me “adjust” the image so that a straight line on this “adjusted” image will be geodesic?
Are there any other free applications out there that do display “adjusted” maps where straight lines on the screen are actually geodesic?
Are there any free applications out there that will provide me with a geodesic path between two points on earth?
Thank you in advance.
First of all it’s clear that the lines are not ellipsoidal geodesics.
For example, the line between (lat,lon) 0,0 and 0,179.99 in Google Earth is shown along
the equator instead of the shorter path going near the pole.
The KML documentation says that the sides of a path are “great circles”
and that the sides of a polygon are “lines of constant bearing”. I
believe that “great circles” become great ellipses (a path along an
ellipse whose center is the center of the earth). An ordinary
understanding of “lines of constant bearing” is that they are rhumb
lines, i.e., that they correspond to straight lines on a Mercator
projection. However, the documentation lies. Instead there are
straight lines on a plate carree projection.
I have asked Google to use geodesics for both sorts of object, and they
are considering this.
I have written a C++ library
GeographicLib which solves the
geodesic problem accurately. If you want to see how to generate a
sequence of points along a geodesic, see the example in the
documentation for the
GeodesicLine
class. If you just want to test the solutions, look at the
online geodesic calculator.