# Camera position in the 3-D Point Cloud Registration and Stitching example

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CBde on 12 Oct 2017
Commented: Behnam Nasirian on 20 May 2018
Hello,
I am going through the example '3-D Point Cloud Registration and Stitching'
(https://de.mathworks.com/help/vision/examples/3-d-point-cloud-registration-and-stitching.html)
and I am trying to determine the camera position in the first and second input image to then display it in the 'Initial world scene' image. But I'm having difficulties with this and would really appreciate some help on this one.
Best, Christian

Prashant Arora on 16 Oct 2017
Hi Christopher,
I believe with respect to each point cloud, the camera is located at the origin. Hence, to show the camera position in the "Initial World Scene", you can show the first camera as:
plotCamera('Location',[0 0 0],'Orientation',eye(3),'Size',0.1);
The second camera can be shown as:
camPosRel = [0 0 0 1];
camPosTransformed = camPosRel*(tform.T)';
plotCamera('Location',camPosTransformed(1:3),'Orientation',tform.T(1:3,1:3),'Size',0.1);
Moving on, you can use the "accumTform" variable instead of "tform" to transform the camera from any point cloud frame ( [0 0 0 1] is the relative position) to the "world" or "initial scene"
Prashant
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Behnam Nasirian on 20 May 2018
This answer seems to be wrong. If camPosRel = [0 0 0 1]; camPosTransformed = camPosRel*(tform.T)'; Then camPosTransformed always will equal to [0 0 0 1].

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