NUKEX CameraTracker Tutorial Part 1: The Basics Video Lecture | Create Visual Effects with Nuke - Professional Skills

welcome to the first in this series of
tutorials on the camera tracker node for
nuke X so this first tutorial is going
to talk about tracking and solving
getting started with a camera tracker
node so I've got an example bit of
footage here it's got a fairly nice
camera move some interesting things
going on for ground movement and we've
got to track and solve past this big
rock here so the way the camera tracker
works is it picks up some 2d points and
if I do two tracks them over time from
the tracks it calculates a 3d fixed
location in the world and the camera
move that matches those 3d points down
onto the movement in your footage
so the key point using the camera
tracker is to make sure it's picking up
and tracking good 2d points so the first
thing you'll notice about the scripts is
I've got a roto here so this is a really
rough garbage map to make sure I'm not
going to track and solve off this guy
who's moving any moving objects is going
to give you bad 3d points in your camera
solve so it's pretty dirty matte but it
will do the job
just make sure we exclude that region
from the tracking
okay so let's bring up the camera
tracker I need to make sure I'm going to
mask out that mat so I'm going to set
the mask to source alpha so these three
steps to using the camera tracker first
of all you've got to track the footage
then you solve the camera then you
create a scene to work with in Nuuk
I'm going to go through each of those
steps so before you track your features
you need to set up your tracking
parameters so the trick here is to
switch on the preview and just make sure
you're going to pick up good points for
yourself
so these need to be the fixed points in
the world they're going to be good for
tracking so the main parameters to deal
with here are firstly the number of
tracks if you think you're going to get
a lot of bad tracks out of the footage
maybe it's a fast maybe there's a lot of
motion blur maybe there's a lot of
foreground movement you might want to
punt this out maybe 250 points because
the aim thing is to get around 100 good
auto tracks for the solve 150 is the
default gives it a little bit of leeway
to lose some so as you step through
you're going to want to set the
threshold to make sure you're picking up
good things so you can see on this frame
got quite a few points in the sky that's
going to want to try and track now sky
points are bad they're a long long way
away you're not going to get any decent
3d locations to solve the camera so
you're going to want to change the
threshold here just to remove those so
as I step through problem moves straight
away you can see it's not picking up the
rock anymore it's a little bit too
blurry to pick up any points now that's
actually really bad because what I want
to do is to be able to track and solve
past this rock and back again and if
there's nothing to solve off the rock
there's nothing to lock the camera down
so I'm actually going to bring that back
down to make sure we've always got good
points to track through the sequence and
we're going to have to deal with these
sky points later on okay let's just make
that a nice round number you can also
play around the separation if you if you
find points cluster in one place you're
going to want to force those apart the
aim is to get some good fixed points
across the whole image at all the
different frames and this in the
sequence all different sections of the
shot
so let's go with that looks pretty good
these more in-depth parameters here are
to do with shots that difficult to track
you might want to increase the
smoothness if you've got a lot of jitter
track consistency of tracks aren't
consistent in the shots maybe if you're
losing a lot of tracks you might want to
reduce the threshold a bit okay so let's
go with that and track so what it does
is it picks up 150 points tracks at over
time every time it loses a track it
tries some bumps up to 150 again it's
going to take a few minutes on my Mac
broke so let's get forward okay so once
it's tracked you want to go through and
review the tracks make sure they're all
locked down on fixed points so we're
worried about the sky before you can see
some points up here and long thin
structures they're going to not be
locked down well it's not too many sky
points but you can see a lot of little
spurious ones here so the first thing
you can do is you can actually manually
go and select those and delete them and
you can step through the time line
picking these things up and deleting
them there's a few bad ones there the
other thing you can do is go into the
refine tab and look at the tracking
information so let's look up a look at
the minimum and average track length so
you can see there are a few tracks here
that are down low some short spurious
tracks so we can do is just lift this a
little bit let's just keep the nice long
ones in check they've got some nice
tracks over sequence we're not losing
whole frames okay let's just go delete
those straightaway
okay so the next step is to solve the
camera so let's look at the solver tab
and set up the solve we have a constant
focal length we don't know the film back
or focal length for this shot you can go
and set the motion that you expect it's
just a free camera is not nodal or
linear planar at the moment we're not
going to set any smoothness and these
parameters are here are really to do
with dealing with bad when the solve
goes wrong okay so let's just go in and
solve so what this does is it steps
through the timeline and it calculates a
set of what's called keyframes so for
the sequence it might come up with five
six seven ten keyframes that define the
motion of the camera it then solves
those to lock down the camera and fills
in the rest of the frames okay so we've
got to solve now it got a slightly
different color scheme for the tracks so
green means it calculated a 3d point
looks good if you look at the overlay
you can see you've got a nice error
that's less than the pixel the red
points the points that thinks are bad so
it's got a large error on that point
that's so you can actually go in that
sense from that track and see what's
going on
by centering on the track and playing
forwards and backwards you can see how
well it sticks to the footage
alternatively you can select a number of
tracks and center on them all to see how
our region sticks okay and the amber
tracks these are the tracks where it
couldn't calculate a 3d point it was
ambiguous so it looks like we've got a
reasonable set of tracks across the
sequence we can do now is go into this
refine tab look at the errors for the
tracks so these are the pixel errors the
error between the 3d point and the 2d
track so the 60 you get tool tooltips on
these curves now which is quite useful
there's two area curves we're most
interested in the track error and the
maximum error per frame what you can see
is there's some tracks here was quite
large errors in there so let's just
bring that down to something reasonable
let's just reduce the maximum error
we're allowing on our tracks okay so now
we've set those thresholds the color
scheme in green is just showing
everything that's below our thresholds
on the error and above the minimum
length on the track length so we need to
make sure we've got some nice green
tracks that are taking us through the
sequence so that looks good so we can
hit recalculate itself now it will just
calculate the solve based on those green
tracks only we want to check that it's
still going to be able to solve okay
check that we've got green tracks taking
us through the whole sequence that seems
good
our reprojection error now is looking
reasonable so I'm going to go and delete
everything that's not useful here delete
all those points where it can calculate
3d points and select the ones that we've
rejected all those tracks in red so
we've just got the good tracks for the
sequence so this helps with the cleanup
I didn't have to go and manually delete
all those Skye points now so let's just
resolve from scratch just using those
good tracks
look at the reprojection error 1.7
pixels okay so the solver looks good if
the salt was bad I would have gone
straight back to the silver tab my first
thing I always do drop down this key
frame separation that just pulls in more
of those key frames to lock down the
camera path you can also another good
tip is to set the first frame it uses
for the solve so here it picked up frame
307 you can actually go in and set which
frame it uses to begin with so you can
try using frames that have lots of nice
parallax and then lots of depth changes
or you can just try different frames in
the sequence to see if it gives you a
better result okay so now that we've
solved I'm going to create a scene so
what that gives you is it gives you your
camera and you to work with it also
gives you a camera track a point cloud
so this just allows you to export with
the right GA and if I switch to 3d now
because see I've got a point cloud and
camera so I can see how well that fits
just look down on the camera
so if you want to start using this in 3d
first thing you're going to want to do
is set a ground plane so you can line up
your world nicely so I'm going to select
a load of these ground points just
switch to 3d make sure they really do
lie on the ground yeah they look good
and I'm going to set the ground plane to
those selected points you can skip along
the timeline picking up points as you go
let's just pick up a few more switch to
3d make sure they're on the ground yeah
they look good set to selected few more
frames let's pick it up some of these
ones further along they're still on the
ground ok so I've got a nice ground
plane now
nice little feature I like is I can go
and set the orientation of the world so
if I pick up these two points set the
said axis to line up with those gives me
nice and orientated so I can set things
in 3d nicely so let's just see how well
it fits so I'm going to create a little
cube here scale it down a little bit
make sure it's sitting on top of the
ground and let's render it how good is
our track
okay now we've got our cube in the right
place we can play forwards and see how
well it sticks it's sticking quite
nicely there's no slippage there at all
and there we go so that's the end of the
first tutorial on the camera tracker the
main steps are you track your features
but before you track just go through
have a preview and set up your tracking
parameters if the tracking doesn't look
good you might want to come back in and
tweak the thresholds and smoothness once
you've got the tracks you need to go
through the timeline and review them
check they look good maybe clear out the
bad ones manually by selecting and
deleting after you happy with your
tracks you hit solve you may want to go
in and set up your solver first and once
you've got your solve go into the refine
tab have a look at the errors tweak some
of the thresholds to make sure you've
just got the good tracks and you can
delete all the bad auto tracks on the
scene once you're happy with your trap
and solve you create a scene