it doesn’t have to be.
If we have one person who can accurately measure error across the sheet, it
becomes FAR easier to test other accuracy improvements.
This is not what I’m doing. I’m taking individual pictures and measuring the distance from the center of the picture to the center of the square that should be in the center of the picture. That gives me an x and y error for a given x and y target. Then, in the controller, I change the target coordinates in triangularInverse to accomodate the error. So if I want to go to -100, -100 and when I tried to get there before I actually went to -102, -103, I change the coordinates to -98, -97. Not perfect, but close.
I used a 2nd order quadratic equation and used numpy’s least-squares (lstsq) routine to fit my calibration data to the equation. The solution was not extraordinarily good but I’m fairly my issue is because I only have data for the bottom left quarter of the board (everything else is zeros). Kinda hard to expect a smooth equation to handle such impulses. If you (or anyone) have any recommendations as to the form of formula or if you have recommendations on methodology for curve fitting, please let me know. I thought you (or someone) posted something for me to look at but for the life of me I can’t find the post.
It was mathworks.
They have a number of types of curve fits. Very full site
What I was hoping to get was delta y values (and delta x values) for a grid across a full sheet. It’s why I suggested on 12” squares.
Then for each ordinate plot the deltas in a “surface plot”. That is a 2 dimension plotted surface of the delta values ( 2 plots, one for x and one for y)
After viewing the surface, then chose several of their surface fits and see how good each is.
The best surface fit should be able to calculate the delta correction for any x,y point, to use somewhere in the maslow software to adjust the chain length.
I wanted to do this without any of the current correction calculations involved. Let this see what the native Maslow does because I think one correction is all that would be needed, not correction on corrections.
Ed
Hopefully this weekend I can post a full sheet’s worth of values that you can use. It’ll be every 3 inches, but you can pick just pick every 4th one 
The problem I might have though with disabling chain sag is that the “raw” equations (uncorrected by chain sag) may be so inaccurate that the camera won’t be able to see one of the squares, but we can try.
Well we’ll find out. Hopefully it’s not that far off. What are the dimensions of your machine? Motor spacing and height.
141 inch motor spacing and approximate 19 inches above worksurface