Geodetic commentary

The Mix up of “X, Y, Z” Coordinates Between Photogrammetry and Geodesy

In Spatial considerations –

In geodesy, the “ZXY” coordinate system is “right-handed”, where the right thumb points towards the Z-axis, index finger towards the intersection of the Reference Meridian and Equatorial planes, and middle ?nger or the positive Y-axes, which is at right angle to the Z- and X- axes and in the Equatorial plane, towards East. The axes are de?ned in the order “Z”, “X”, and “Y”.

Clarifications

a. The origin is at the Earth’s center of mass.

b. The reference meridian is as realized by the ITRFyy (nn.0), not by the “Greenwich”.

c. The origin of the reference ellipsoid is coincident with the origin of the 3-D “XYZ” Coordinate System

In photogrammetry, the “ZXY” coordinate system is “left-handed”. Here, the main difference (from the geodetic system) is that the left middle ?nger or the “positive” Y-axes points towards West.

On the Photo Platform –

Here, the “X and Y” relate to the horizontal and “Z” relates to the elevation.

NOTE: The “Z” of the photo platform should NOT be mixed up with the “Z” of the 3-D rectangular coordinates of a geodetic system, e.g., WGS 84.

		Muneendra Kumar Ph.D. is Chief Geodesist (Retired), US National Geospatial Intelligence Agency munismk@yahoo.com