3

I want to put on a QGIS map some historical sites to check if they are aligned. If an alignement exists, the points should stay on a great circle (is this correct?). I want to visually verify this using a map projection where orthodromic lines are represented as straight lines. In a second step I would draw two boundary lines and calculate bearings from a determinate point.

For example, here is a snapshot of a QGIS map with the points of "The St Michael-Apollo 'Axis'" as described by Lucien Richer, 1977.

enter image description here

Map boundaries: (-11E, 32N) (36E, 52N). EPSG 3785 projection (popular visualization / Mercator) .

My questions:

  1. What would be the most appropriate map projection to get great circles as straight lines?

  2. Do I need a custom projection? If yes, what are the parameters to use in QGIS?

Any suggestions would be helpful.

  • 3
    What part or extent of the world do the sites cover? Can you describe in a bit more detail what you mean by 'at what degree they are aligned'? Does that mean angles, between boundary lines or relative lat/long positions/differences or something else? Can you provide a graphic example? – Chris W Jun 28 '15 at 18:07
  • Ah, it's a "ley line" or something similar. Azimuth equidistant with a customized center point, or gnomonic where all straight lines are great circles. One question is: what sphere/ellipsoid should you use? – mkennedy Jul 1 '15 at 21:25
  • If you don't want to use a custom projection, you can accomplish this work flow with two projections: a Gnomonic projection to check for alignment and a Mercator projection to calculate bearings. – whuber Jul 4 '15 at 15:30

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.