I was interested in the source as some example of the pipe and data-passing mechanism.  My answer to most of your questions above is - I don't know :) (which is why I was looking for some example code).

Having said that, I'm pretty comfortable saying that using a separate .exe for just (individual) point-in-tri tests would be a waste of time and effort.  The overhead involved in calling it  thousands or tens of thousands (or even hundreds of thousands) of times would out-weigh any benefit of having it compiled.  It's possible that even doing (just) that with a .dll would be a waste of time.

To get any real benefit, you want to do all the looping through the tables in C as well.  I hadn't looked closely at your shrink-wrap code, but I'm sure it's doing something similar to the linecast_loop().

As for using strings/files - I'm not crazy about that idea. It's a lot of data to be converting to strings and/or creating files for.  Ideally, there'd be some way to pass a pointer to the array to the C code, which could then do whatever it needed to do to access that array of values.

Maybe ADP has some suggestions/thoughts/sample code?

My trouble is that I'm not familiar enough with Python and/or the Python<->dll mechanism and don't have lots of free time to go investigating it.  If you want to do some leg-work tracking down some links to info and/or sample source code showing how this is done, I can spend some time looking at it.

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