Using <window>.screenToWorld within vizcave powerwall

[VizMars]

Thank you for providing this link. Afaiu d and z (in the example you linked) are two variables that hold standardized depth values, and z is used to construct the color for the depth texture.
I have a two questions regarding this example:
1. Can you explain what exactly d and z correspond to? And if they are standardized, is it also possible to get the unstandardized distance/depth information?
2. How can I get these values (d and z) for each pixel?
viz.window.screenCapture() allows me to save the screen image to a file where I can extract the r, g and b values from (not sure how they correspond to d and z) - but I think it would be better to get the depth information within Vizard. Is this possible?