Linear vs Perspective/ Splits

[gcooke]

Hi,

I am working on a show where I will need to map some surfaces to flats onstage that have corners and are not oriented perpendicularly to the projectors.  I have been looking through the Qlab Video Surface Editor user's guide and I wanted to check on a few things:

Linear vs Perspective:  if I am not "concerned" with perspective correction, then I want to use Linear, correct?  For example, I have Text Cues that move across the stage and set. In my prototype test work, I notice that, in perspective warps, the text will move slowly through areas of greater perspective warping, which makes sense.  So, If I want the text to move "evenly" (in terms of rate) across the flats then I should use linear warping?

Splits: In working with Splits, I notice that the closer I assign a split to a corner, for example, the less distortion will occur when I adjust the corner point, which, again, makes sense.  I want to confirm that I can't "preview" the "x" or "y" setting prior to making the adjustment.  The process is: select horizontal or vertical, select the x and y point, then adjust the corner point to see how close the split is to the corner of the flat.  If its too far(resulting in too much distortion), then I can either undo the above steps or delete the split.  Then redo the split with an adjusted x or y value.  Just checking that I am not missing something.

Thanks!

-George

[Steven Sokulski]

If the end result is a single flat surface (for each video surface in QLab) to function as a rectangular screen, I think a Perspective Warp would be ideal.

I've copied the relevant part of the docs referring to Perspective Warp here:

an image in one part of the surface will appear exactly the same size if moved to a different part of the surface

You can read more under the following heading:

http://figure53.com/docs/qlab/v3/video/surfaces/#warp-type

Basically, a Linear warp is best-suited to more complex shapes where you need to use splits to wrap onto something non-rectangular.

For corner-pinning, you're better off with Perspective warps.

[Stephen Harrison]

It sounds like you want to wrap a single surface around more than one face of an object onstage, in which case you will want to use a linear warp with splits, as Steven says.

For the split at the corner, you want to set the split point to be the logical point on your surface where the corner occurs, and then map it to the corners of the object onstage. This way you will have the correct perspective across both surfaces. Your surface, and split(s) should scale to match the dimensions of the physical objects.

Simple example:

You have a surface that is 2000 x 1000 px that represents two sides of a cube onstage. Each side of the cube is represented by a 1000 x 1000 px area in your surface.

Split the surface horizontally at x=0 and then pin the 6 control points onto your surface.