Question: extract the z value of a 3dplot

I want to display a 3dplot of a current

iL_RMS_3dplot_Ue_const:=plot3d(iL_RMS_func_Ue_const, 0..2, 0..1, axes=normal, title="RMS current through the inductor with Ue constant and Ua variable", labels=["Ia_IaLGmax", "Ua_Ue", "iL_RMS_Ue_const"]);

together with an output curve. The output curve (which is two dimensional) should have as the z value in a 3d plot the value of iL_RMS_3dplot_Ue_const at that place. I have uploaded an example to (the blue curve is the output curve). Is it possible, without recalculating the z value with a function to call, to extract it from the iL_RMS_3dplot_Ue_const plot data structure with an op command or something similar. The 3dplot command for the output curve should look somehow like this:
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