Scara kinematics

I've configured my scara robot so all joints are homing nicely. In Axis, when I jog the Z axis in a negative direction (down), the end effector physically moves down. So far, so good. But it moves 'up' in the 3d window.
In the ini file, traj coordinates are XYZC and Display geometry is the same.

If I switch display geometry to XY-ZC Then the motion on screen is coordinated with the machine but everything else is inverted. Z "up" is below Z 'down' if that makes sense.

I've tried inverted the axis by changing the encoder scale and output scale, but then jogging negative goes up and vice versa. So I don't think my issue is hardware configuration. I think it's related to the kinematics.

in scarakins.c there's a comment:

That leads me to believe my joint[2] needs to be negative. But I don't know how to set that.

Am I barking up the wrong tree?

I thought so too but that's how the scarakins.c file is now in master. Is this a difference between joint mode and world mode?

Ok, that worked! I had to invert the Z in the inverse section as well.

github.com/LinuxCNC/linuxcnc/blob/master...ics/scarakins.c#L162

It's not a high priority but scaragui is reversed as well. Any idea where I flip that one?

I'm also finding that while I can jog in joint mode consistently, in world mode, I get following errors at places that should be well inside the usable envelope. These errors happen regardless of the jog speed but happen consistently at certain places. For example, I'll get following errors jogging at 100 mm/min in one part of the table but can easily jog at 6000 mm/min in another. As far as I can tell, it's nothing mechanical since each joint can move at maximum speed in joint mode in the same area.

Advice on how to troubleshoot this would be appreciated.

No. This is inside the rectangular area that can be reached without inverting. As far as I can tell, there's nothing special about it..

Sure but I might need a bit more guidance setting this up. My halscope kung-fu is pretty weak.

Do you mean the a-pos-cmd on the signals tab in halscope? Not sure what that corresponds to as I have joints 0,1,2,3 joint mode and axes XYZ in world mode.

A screenshot or guide how to set up halscope to capture this kind of error would be very helpful.