# SaveMotion: xpos and zpos

Hi everyone!

For example looking at examples/mdbc/07_WavesCylinder, I see xpos and zpos being given as xpos = 2.2 and zpos=-0.1.

I understand xpos = 2.2 since it is the middle of the cylinder, but I do not understand zpos completely. In the XML guide it is defined as "zpos=-depth", so if depth = 0.5, then by default zpos=-0.5, which means that we measure the analytical solution at the seabed?

But when zpos is then defined as zpos = -0.1, then we set the zpos outside the water surface?

Could anyone explain it to me?

Kind regards

## Comments

SAVEMOTION allows you to compute the THEORETICAL values so xpos and zpos are no more related to our SPH domain, but they will be:

Regards

Ah okay thanks a lot! So basically we take the mean water level of the analytical solution minus zpos, and measure the properties at that point.

Makes sense.

Kind regards