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Place Tool: Automatic coordinate system setup
SynthEyes offers a tool that can set up a coordinate system automatically: one click, or even none. It's a nifty algorithm that looks at all your trackers to make a decision. But, before you start celebrating and decide to ignore the rest of the "Setting Up a Coordinate System" chapter totally, here's the bad news:
- if the automatically-chosen coordinate system matches what you want to do, it is mainly because you are lucky,
- most trackers that are "on the ground" are really on objects that are sitting on the ground, and therefore somewhat above it,
- many buildings and sets are rarely exactly flat, and the ground almost never so,
- the automatically-chosen coordinate system will tend to be a good rough approximation to a plane of interest but it will never be exactly right for a
particular use therefore
- the automatically-chosen coordinate system will effectively cause sliding, unless you refer to nearby trackers to place your objects.
To say this another way: the Place Tool makes it easier to create a coordinate system, but harder to insert objects accurately.
The Place Tool examines the relative positioning of all the available trackers, and is intended for automatic tracks, which produce many trackers, not for supervised tracks and not for object tracks, which have too few trackers for the Place tool to analyze.
Outdoor scenes may have too much of a jumble and too little structure for the Place too, so any choice will be just as bad or good as any other. Nor is the Place tool suitable for Tripod-mode nodal tracks, which aren't 3D solves. It will work fine with stereo tracks, however. And you can use the Place tool for scenes with camera and object tracks, to set up the camera track: the object will be carried along, though you will still have to manually set up a coordinate system for the object itself.
You can find the Place tool on the Summary Panel: it's the button named Place next to Coord. When you click the button, SynthEyes will analyze your trackers, determine a coordinate system, then reposition the entire camera path and trackers
accordingly. (It moves meshes too, unless you have turned off Whole affects meshes on the right-click menu of the 3-D or perspective viewports.)
The Place tool can also run automatically after you click the full AUTO track and solve button
, if the Run auto-place checkbox is checked. (The first time you click AUTO, you will be prompted for whether you want auto-place or not.) If the Place tool has run automatically, but you want to use the three-tracker method, go ahead!
The Place algorithm proceeds through five main stages: plane, rotation, origin, scale, and results.
In the plane stage, it looks for a large collection of trackers that form a flat plane, which might then be made into a ground plane, a back or side wall. Keep in mind that SynthEyes examines only the position of the trackers, it does not understand what the trackers are on. SynthEyes decides whether to use the plane as a ground, back, or side plane based on its relative orientation to the camera.
In the rotation stage, it rotates the scene around in the plane, looking for a rotation that causes many of the trackers to line up. For example, if SynthEyes has found a ground plane, as it rotates the scene it may find that many trackers line up when the axes are parallel to trackers on the back wall of the set.
In the origin stage (which itself has two steps), having decided on the plane and rotation, SynthEyes decides where the origin should go, by looking along each coordinate axis for a spot where many trackers are clustered together. That spot becomes the zero coordinate for that axis.
In the scale stage, SynthEyes enforces any pre-existing distance constraints, or if there are none, it adjusts the median scene size to a fixed nominal value.
IMPORTANT : If you have a measured distance from the real set that you wish to use to set the size of the scene, while still doing an automatic placement, you must set up the distance constraint before hitting Place!
In the results stage, each tracker that is part of the plane is set up with a Lock to the coordinates calculated for it, and it is selected, so you can tell which trackers were used for the plane.
So to summarize by example, consider an ideal case where the shot is of the inside of a room towards the back right corner, with trackers on the floor, a back wall, and some on the right side wall. SynthEyes picks the trackers on the floor as the ground plane (Z=0 with Z-up coordinates), spins the scene around so that the trackers on the back wall become parallel to the X axis, finds that clump of trackers on the back wall and sets them to be at Y=0, and finds the clump of trackers on the right wall and puts them at X=0. So the overall scene origin is in the back right corner of the room, which is a nice choice.
If there were more trackers on the back wall, SynthEyes might use the back wall as the plane, spin the scene around the back wall until the floor was level, then place the origin the same way, so we'd still get the same result.
Of course, the real world is always more complex. Often there are multiple solutions that are just as good as each other, and the Place tool may give you a solution that isn't what you are looking for.
The Place Tool offers a simple solution: click the Place button again! By design, the tool randomizes the solutions, so each time you click the button, you'll get a different solution. If there's really only one good answer, you'll see it almost all the time; if there isn't a good choice you may see radically different solutions each time. Be sure to look carefully in the Quad view to assess the coordinate system. If you like it, do NOT hit Place again! Each Place is different; you can get back only by using Undo.
You can control which trackers will be considered as potential members of the plane: if you hold down the SHIFT key while clicking the Place button, only the currently-selected trackers will be considered. You can use this feature when you want the plane to definitely come from one particular part of the scene where you want to do an insert, for example. You can also use it after an initial Place, if you think the chosen plane is a good choice, but contains a few inappropriate trackers. Shift-click those trackers to de-select them, then shift-click the Place button to recalculate using only the remaining trackers.
When the Place tool runs, it produces a whole set of coordinate system locks, on each tracker used for the ground (or wall) plane. This system of constraints allows the same coordinate system to be re-established, even if you subsequently solve the scene, not only with a Refine-mode solve, but even starting over from a Automatic-mode solve (note that that's different from the AUTO button on the Summary panel). If the tracking data has changed around significantly, you'll still get the best approximation to the previous coordinate system.
If you want to adjust the placement created by the Place tool, you can use the Manual Alignment method described below. You might want to adjust the position of the plane if it is actually a little above the true ground level. As you do that, the manual adjustment will be adjusting not only the tracker and camera positions, but the lock coordinates as well so everything stays consistent.
Once you've used the Place tool and decided on the coordinate system, stick with it! You want to keep your existing coordinate system, or at least something very close to it, once you have positioned objects in the scene, either in SynthEyes or downstream in your animation package. You don't want to have to re-do any manual adjustments or the object positioning if you correct a bump, for example (though you might have to tweak them slightly).
To avoid interfering with your existing Place-generated coordinate system
- do not hit the Place button again! (Click Undo if you do by mistake!)
- do not turn on the Constrain checkbox on the Solve panel, as that will force the trackers to have their old coordinates exactly, distorting the scene.
If you update the trackers and re-solve, you'll see small errors in the Constrained Points view, but they are OK. If they bother you and you want to set them back to zero, right-click in Constrained Points and select Update all locked. It will update the trackers to use their current solve coordinates as the Lock-to values, so there will be no error.
Important : to avoid sliding when inserting an object, you must position the object relative to the trackers near to it. If you see the object sliding with respect to a spot in the imagery, create a tracker on that spot, and use that tracker as a basis to reposition the object. Sliding is a user error!
If the Place tool has run automatically (or manually) and you decide you want to set up a coordinate system using the three-tracker method instead (and we'd rather you did), that's no problem. Click the Coords button on the Summary panel or *3 on the Coordinate System panel, and it will first delete all the existing constraints created by the Place tool. You can proceed to click on your three trackers to create your coordinate system normally. (Or in the Constrained Points view, right-click/Clear ALL constraints.)
©2024 Boris FX, Inc. — UNOFFICIAL — Converted from original PDF.