<div dir="ltr">Hi Naimul,<div><br></div><div>Be careful, you're not using the same definitions as one ones that I gave in my email.</div><div><br></div><div>I defined the Z axis as pointing out the back of the camera, not out the front. That is the way the camera's local coordinate system is defined for VTK (and for OpenGL). So:</div><div><br></div><div>1) Given my definition of the zvec, the equation for the focal point should be the following:</div><div><br></div><div><span style="font-size:12.8000001907349px"> camera.SetFocalPoint(pos[0] - d * zvec[0], pos[1] - d * zvec[1], pos[2] - d * zvec[2]);</span><br></div><div><span style="font-size:12.8000001907349px"><br></span></div><div><span style="font-size:12.8000001907349px">2) for the Aurora tool, if the tool's local Z axis is pointing out towards the "focal point", then you actually want to rotate the tool's coordinate system by 180 degrees around the tool's Y axis in order to generate local coordinate system for the camera.</span></div><div><span style="font-size:12.8000001907349px"><br></span></div><div><span style="font-size:12.8000001907349px">I know this is pedantic (since you end up with two 180 degree rotations that cancel each other out), but this can be important if you want to do any operations within the camera's coordinate system.</span></div><div><span style="font-size:12.8000001907349px"><br></span></div><div><span style="font-size:12.8000001907349px"> - David</span></div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Aug 25, 2015 at 2:54 PM, Naimul Khan <span dir="ltr"><<a href="mailto:naim.13@gmail.com" target="_blank">naim.13@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">That worked, thank you so much! For anyone looking at this thread, this is the right solution. To add to David, in my case, I wanted the focal point always at a certain distance along the camera's local Z axis. To compute that, just do the following in addition to what David did:<div><br></div><div>camera.SetFocalPoint(pos[0] + d * zvec[0], pos[1] + d * zvec[1], pos[2] + d * zvec[2]);<br></div><div><br></div><div>where d is the distance. </div></div><div class="gmail_extra"><br clear="all"><div><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><br><div>Regards</div><div>Naimul Mefraz Khan</div></div></div></div></div></div></div></div><div><div class="h5">
<br><div class="gmail_quote">On Thu, Aug 20, 2015 at 11:55 AM, David Gobbi <span dir="ltr"><<a href="mailto:david.gobbi@gmail.com" target="_blank">david.gobbi@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Thu, Aug 20, 2015 at 7:47 AM, naimulkhan <span dir="ltr"><<a href="mailto:naim.13@gmail.com" target="_blank">naim.13@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">hi David,<br>
<br>
I am in the same boat as the opener of this thread. I am trying to use an<br>
external tracker (NDI Aurora) to control the vtkCamera (basically "look<br>
through" the position and orientation of the tracker). I can set the<br>
position through vtkCamera::SetPosition() easily, but I am not sure what<br>
parameters SetViewUp() and SetFocusPoint() should be called with. Any help<br>
would be greatly appreciated, thanks!<br></blockquote><div><br></div><div>Consider: any frame of reference can be described by a point and two unit vectors. The "point" is easy, it's the camera's Position.</div><div><br></div><div>The first unit vector that we will use is the camera's local Z axis, which points _away_ from the focal point, i.e. it points out the back of the camera. In other words, its direction is from the FocalPoint to the Position.</div><div><br></div><div>The second unit vector that we will use is the camera's local Y axis. This is just the ViewUp direction.</div><div><br></div><div>I advise taking a look at Figure 3.9 on this web page: <a href="http://www.glprogramming.com/red/chapter03.html" target="_blank">http://www.glprogramming.com/red/chapter03.html</a></div><div><br></div><div>So, let's say that you have a vtkTransform that describes where you want to place the camera. How can you get the position and the two vectors? Easy, just apply the transform to the origin, to a unit z vector, and to a unit y vector:</div><div><br></div><div>double pos[3] = { 0.0, 0.0, 0.0 };</div><div>double zvec[3] = { 0.0, 0.0, 1.0 };</div><div>double yvec[3] = { 0.0, 1.0, 0.0 };</div><div><br></div><div>transform->TransformPoint(pos, pos);</div><div>transform->TransformVector(zvec, zvec);</div><div>transform->TransformVector(yvec, yvec);</div><div><br></div><div>That's as far as I'll go, you should be able to figure out the math for computing the FocalPoint from the Position, the zvec, and the Distance from the camera to the object it is looking at.</div><span><font color="#888888"><div><br></div><div> - David</div><div> </div></font></span></div></div></div>
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