Putting aside any particular use case, let's say that I, a developer relatively new to the .NET programming interface for Autocad 2013, wanted to fully understand how coordinate systems and transformations using objects and methods such as BlockReference.BlockTransform, BlockReference.TransformBy, Matrix3d.WorldToPlane, etc. etc. on and on, where would I go for full documentation? I am able to create a new command and debug into my code (i.e. I have a fully functional development environment), but it doesn't seem to be helping me much to understand what these APIs are doing. Trying to reconcile the current user coordinate system with point values I am seeing in the debugger and what simple rotational transformations are doing is proving difficult without docs and explanatory diagrams. Any help pointing me in the right direction is much appreciated.
The ObjectARX Developer Guide (arxdev.chm) is definitely the place to start. Download the ObjectARX SDK free from www.objectarx.com
I answered my own question largely by writing the tool I needed in .NET. Here is a link to the post, including an attached DLL.