{Help Pls} Coordinate work of curves and Interpolation

Question

I am a newbie on VB, really have no idea to do my project. Could you please go through my case and see whether you could help me solve !and Please forgive my bad English expression. If you know any part ,pls give advices as well ! Say I already have many train's wheel profiles which measured by a system and the x,y coordinate datas are stored as txt files. Each txt file represents a particular wheel 's profile x,y coordinate measured in a particular time. As wheel will wear so the profile curve will be different at different time measurement. I have 3 software have to be programming A.Thickness against Time curve What I dont know is : 1. If I want to choose a period time of wheel profile text files to be used ,how to do it in VB? 2.After that , I need a y coordinate variable or array to be set (e.g.line 1 or line 2 value so that i will get two intersection points ,point A & B if set the y varibale at line 1 value and get C & D points if set the variable at line line 2 value). And i need is that i choose a period of time of wheel profiles and enter a y variable in my program and after click plot button . The program will plot out a thickness against time curve but there is a big problem has to solve is that when enter a y variable which is 10.22 mm so the wheel profile txt file have no that two intersection points and how to do interpolation to find the 2 intersection points and calculate the thickness by using point B minus point A ,etc.? B. Wheel rim Slope against Time curve what i need is: 1. If I want to choose a period time of wheel profile text files to be used ,how to do it in VB? 2. When i set two constant x coordinate in the wheel profile curve , i will get two y points so slope = y/x ,but how to set constans in vb C. Animation of wheel profiles curve decay Final thing to do is : User could select a time interval for the amimation to display and program will show the animation of the wheel profile changes. The wheel trace will show the worn situation gradually same as an animation. For making the animation, a background color line will be used to cover the old one, and then show a new one in another color. In the display, you will see that the decay process looks like the animation.