Bed leveling UBL delta printer

[Roxy]

UBL now works with Delta printers. (oldmcg did the work to get it running in that environment.) A good place to start would be showing us your bed's Topography make. Do a G29 T and post the results here.

With Delta's there is a peculiarity. You need to also set the mesh points that are outside of the DELTA_PRINTABLE_RADIUS. For Delta's you can enable UBL_G29_P31 which will give you a Least Squares Fit interpolation.

#if ENABLED(UBL_G29_P31)
                case 1: {

                  // P3.1  use least squares fit to fill missing mesh values
                  // P3.10 zero weighting for distance, all grid points equal, best fit tilted plane
                  // P3.11 10X weighting for nearest grid points versus farthest grid points
                  // P3.12 100X distance weighting
                  // P3.13 1000X distance weighting, approaches simple average of nearest points


                  const float weight_power  = (cvf - 3.10) * 100.0,  // 3.12345 -> 2.345
                              weight_factor = weight_power ? POW(10.0, weight_power) : 0;
                  smart_fill_wlsf(weight_factor);
                }
                break;

Let's start with the Topology map and see what makes sense.

[Derv]

I followed a few posts of yours roxy, excelletn work by you and oldmcg. my process was

M502
M500
g28
g29 p1
g29 T
g29 s1
g29 p3 t
g29 p3 t
g29 s1
g29 a
m500
reset the machine
then tried a g29w says its active.
then g26 which made it drag across the bed as if its too low

I did wonder wether it was my z-probe offset that was wrong but i tried everythign from -1.4 to 4.5 with the same result. My probe is on my nozzle it activates about .4 lower than the bed (if that makes sense)