How to calculate orbit parameters of an impacting NEO

[Bioman222]

What are all the equations and inputs necessary for finding the orbital parameters (eccentricity, speed, etc.) of a near earth asteroid impacting Earth, and how do I crunch them? I am writing something and need these. 

[Shpaget]

For orbital parameters you need position and velocity.

[Green Baron]

A quick search revealed for example this and this as introduction, this describes it quite good i think. I want that Takahashi refractor in the last link.

Edit: Here are the equations, beware of coordinate systems. You'd probably have to rearrange them because you come from the other side, you have positions from observations. How about using a ready made software for that ?

Data to play with seems to be available as well: http://ssd-api.jpl.nasa.gov/

Maybe that helps.

Edited January 2, 2017 by Green Baron

[kerbiloid]

This book contains a plenty of formulas to accurately calculate orbits, eclipses and other things.
All of them are implemented in C++ programs (CD applied).
4th edition or later.

Edited January 2, 2017 by kerbiloid