2. A Coordinated Attack

Going from the 3D Earth with its curvature, meridian convergence, and terrain variations to a 2D horizontal coordinate plane will introduce distortions. For some mapping applications, it might be possible to ignore the distortions if they are below the map's resolution. For most surveying applications, however, distortions could have significant impact on accuracy and have to be considered.

There are two ways to control distortions

• Minimize their effect in the first place. It's not possible to eliminate them entirely, but it is possible to design a system which keeps them with an acceptable tolerance.
• If they behave systematically, we can eliminate them by computation. To do this, we have to define and maintain mathematical rigor throughout the 3D to 2D process.

In this topic we will examine

• How grid coordinate systems are developed
• How to convert ground measurements to grid and vice versa.