Camera Tracking - Nuke 101: Professional Compositing and Visual Effects - page 427

You can see that the points are spread out in a way that shows something flat at
thebottomandsomethinguprightontheright.Thebottomthingisthepointsrep-
resenting the table while the upright points represent the picture frame. You want
to make the table flat, not diagonal like it is at the moment.
Youcanonlypickpointsinthe2Dview,butit'sbettertoseeyourselectioninthe
3D view—so you need two Viewers. Let's create a second Viewer.
4. Choose Split Horizontal from Viewer1's Content menu ( FIGURE 10.17 ).
Figure 10.17. Splitting a pane horizontally.
5. In the new pane, choose New Viewer from the Content menu ( FIGURE 10.18 ).
Figure 10.18. Creating a new Viewer in a new pane.