# Simulation 3D Lidar Z-coordinate is wrong

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Bram Surewaard on 1 Feb 2021
Answered: Shubham Rawat on 5 Feb 2021
Hey,
I'm using the Simulation 3D Lidar block from Simulink and I noticed there is a problem with the z-coordinate of the data.
When doing the "Lidar SLAM in 3D Simulation" example the z-coordinate of some of the points are below the surface of the road.
The sensor is located at 1.57 meters above the ground so I would suspect the lowest point being -1.57 however there are plenty of point that are lower than that, with the lowest being around -3.
How is this possible if the ground is flat?
I also tested it in different scenes including the completely flat and empty "Open Surface" scene and in all the cases the z-coordinate seems wrong.
Thanks

Shubham Rawat on 5 Feb 2021
Hi,
I have used an example Lidar SLAM in 3D Simulation and I have found that minimum value of Z axis -1.5938. You may run this code sinppet and check:
minim = zeros(1062,1);
for i=1:1062
% out.ptCloudData.signals.values(:,:,:,i);
ptc = out.ptCloudData.signals.values(:,:,:,i);
minim(i) = min(min(ptc(:,:,3)));
end
min(minim)
Hope this Helps!

R2020b

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