ARSCNView projectPoint returning incorrect data

Question

Created Oct ’20

Replies 1

Boosts 0

Participants 2

Hi. Since upgrading to iOS 14 I have noticed that AR measuring apps have started projecting points and lines that are behind me, in front of me. Tracking this issue through my own measuring app I'm getting inconsistent results between a phone on iOS 13 and 14.

Repeating the same conditions on iOS 13 I am getting a z value returned from the function that is < 0 when the point is behind the near plane. In iOS 14 I am getting a value of 0.4 which is breaking code designed to handle points and lines behind me.

Is something I can expect to be fixed, or something I should just handle post iOS 14?

Boost

Answer 1

DTS Engineer OP

Apple

Oct ’20

This projectPoint method may have been updated in iOS 14 to respect the usesReverseZ property.

When usesReverseZ is true (the default), a point in front of the near clip plane should project with a z-value that is greater than 1, and a point that is behind the near clip plane should project with a z-value that is less than 1.

So a couple of things to check:

If you set usesReverseZ to false, do you see the same behavior you saw in iOS 13?
You say that you are getting a value of 0.4 for a point that is behind the near plane, this is actually the correct behavior, so if you didn't wish to set usesReverseZ to false, then you could update your check based on the correct behavior.

0