# What type of coordinate system is this?

In case you want to say spherical coordinate system: no it is not a spherical coordinate system.

I found this image in a book about flight management systems where they explain the different types of coordinate systems it can use.

The ukrainian name for it is: "ортодромічної" coordinate system

What is the English name of this coordinate system and what advantages may it offer over another (eg spherical coordinate system)?

• 1. "ортодромічної" seems to translate to "orthodromic", i.e. "great-circle based" (en.wikipedia.org/wiki/Great-circle_distance). 2. What is P0? the destination? 3. the fact that it is not using the poles does not mean it is not a spherical coordinate system, just rotate it and it will match a "standard" spherical coordinate system 4. "standard" because any system that has 2 angles and 1 radius (in this case this is fixed) is a s.c.s. Jun 16, 2017 at 17:27
• I can't read Cyrillic, so this does not help me much :|. To answer your comment, I don't know, it might be convenient for the programmer given the requirements, or it might be a convention used in Ukraine/ex soviet countries. Jun 16, 2017 at 17:31
• no, but I am not an expert in the field. IMO, you might have better luck on GIS.SE, but you have ask a mod to move your question there. Jun 16, 2017 at 18:11

By using an online OCR tool (I used this one which is not so good) on page 177 of the document, and then translating from Ukrainian using Google Translate:

... I can confirm @Federico 's suggestion: This figure doesn't introduce a new coordinate system, it just tells about rotating a good ol' geographic coordinate system to facilitate navigation / calculation.

A GCS is defined by its equator, rotating it means the equator is not anymore the Earth equator.

Such frame transformation is also used for INS (SINS) to minimize the accumulation of rounding errors. Just changing the frame orientation allows a better use of the same sensors.

This document says, with fig 7.7, that in some cases, depending on the type of mission or route of the aircraft, it is appropriate to rotate the usual GCS (latitude, longitude) to facilitate calculations and increase accuracy of the results.

An example is, when following a great circle (orthodromy), to align latitude and longitude so that the system equator is parallel to the great circle to follow.

You will easily improve both the OCR rendering and the translation by spending some time on it.

I made this answer a community wiki, so anyone can improve it.

• I don't really speak Ukrainian but I disagree with @Federico. In p.176, first phrase after the title, the 'orthodromic' coordinate system (CK- funnily translated as UK) in question is listed with the geodesic, normal spherical and many others as a standalone coordinate system. According to a random user I just found in an airplane navigation forum Russian navigation has a large orthodrome-related terminology ("Russians made love on orthodromes"). I couldn't find the English equivalent. Jun 16, 2017 at 21:54
• P0 is probably the flight destination. The coordinate system is spherical and x,y can be given as an angle or distance. Jun 16, 2017 at 21:54
• What do you mean by "geodetic CS of an aircraft"? A geodetic frame of reference would be EFEC, not moving with and centered on the aircraft as does a body CS.
– mins
Jun 17, 2017 at 9:02
• (sorry for replying late) I mean a CS centered around the CG with z pointing in the same direction as the gravity vector, x usually points north. The correct name (which I didn't know until now) is "aircraft carried normal earth axis system". Jun 19, 2017 at 22:56