Graphics Reference
In-Depth Information
Notethatrotation-onlycameramotionsuchasatripodpandoesnotprovideparallaxinformationandcannot
beusedtore-create a3Dscene.Youcangetaccurate fixed-camera rotationusingtheTripodMotionoption,but
thiswillnotbuilda3Drepresentation ofthescene.Whenpossible,youshouldalwaystakeextrafootageofany
scene youwant totrack with some lateral camera motion. Youcan build the 3Drepresentation with the parallax
of this extra footage.
Camera Information
The camera solver requires accurate information about the focal length and the sensor size of the real-world
camera the footage was taken with. Blender has some built-in refinement capabilities, but this will usually not
entirely take the place of knowing the specs of the camera and lens used to shoot the footage. There is a col-
lection of presets with many of the best current video cameras included. The footage included was taken on a
Red Epic camera, and I used these values to start with. I didn't know the exact focal length, though, so I had to
relyonBlender'srefinementfunctionalitytogetitright.InadditiontospecifyingaRedEpiccameraintheClip
Editor, I changed the 3D view's camera to a Red Epic in the Properties window.
Checking the Tracks
Before you try solving the camera, it's a good idea to give the markers a once-over with the best motion tracker
in the world: your own good-old human brain. You can do this by watching only the movement of the track
pointsthemselves. Mutetheimage bypressingM,anddisable thedisplay ofpatterns, search areas, andpathsin
theProperties shelf. Figure10-19 showsthetracked footage withtheimage background,withtheimage muted,
and with pattern, search, and path display disabled.
Play the footage like this, so you can see only the track points moving. You should notice two things: First,
the 3D space should be implied by the movement of the points. The human visual system is incredibly good at
reconstructing spaces and shapes from moving points, and if it looks like a mess to you, it's going to look like
a bigger mess to the camera solver. Second, problem tracks should pop out fairly obviously. Watch the footage
a few times all the way through and pay attention. If a single track seems to slide in a strange direction or get
stuck, then you need to look more closely at that track. Most likely, the track is coming loose from its feature
and needs to be disabled for the frames where it's not accurate, retracked, placed by hand, or deleted.
When you've done all this, click Camera Motion on the Solve panel of the Tool shelf. When you do this, the
camera-solver algorithm will trytoreconstruct the3Dscene andthecamera motion.Theresult ofthealgorithm
is the creation of 3D markers, which represent points in the 3D space that should correspond as closely as pos-
sible to the 2D tracking markers you placed.
Troubleshooting the Solve
Viewed through the camera, the distance between a 3D marker and its corresponding 2D tracking marker in
pixels is its solve error for a given frame. The average of the solve errors over all the frames for all the markers
is the average solve error for the scene. This average solve error will appear in the header of the Clip Editor.
You can look at solve errors for individual markers by checking Names and Status on the Display panel in the
Properties shelf.
 
Search WWH ::




Custom Search