= GEOS RFC 8: Improve Coordinate Sequence API (WIP)

||RFC 7:  ||Improve CoordinateSequence API||
||Author: ||Martin Davis        ||
||Contact:||martin-dot-davis at crunchydata.com    ||
||Status: || ||

This document proposes to modify the Coordinate Sequence API to improve performance and adaptiveness.
These improvements are (likely to be) breaking changes to the C++ API.
These may require extensions to the C API to be externally available, but should not result in breaking the current C API.

=== Background

The Coordinate Sequence API as it stands imposes a large cost on clients.
 * It requires copying coordinate list structures one or more times
 * It imposes the cost of a Z ordinate even if not required by the client

The API also has some functional limitations:
 * it does not support M values
 
=== Goals

 * Allow using external coordinate list structures with no copying (except as needed by GEOS algorithms, e.g. removing repeated points)
 * Prevent mutating of external coordinate structures
 * Support XY, XYM, XYZ, XYZM efficiently