Thomas, we have already one guy making the linear regression to fit a quadractic surface into the points collected. But quadractic is not always a good solution for a given non-linearty. Unfortunatelly some of the non-linearities can´t be fitted by quadractic shapes. Because of that, I believe we start to depend a lot on insights for each particular tablet, and we need to make thousands. It seems not very practical, now, but I may be wrong.
The idea of using triangles is because we are going to use two vertices of each triangle as the "basis" for the transform. Once we know in which triangle we are, we can use the "basis transformation matrix" for each triangle, and all calculations will be linear and fast. I believe this is a type of interpolation. My concern in this case is when you move from one triangle domain to another. Straight lines will suffer a lot in this case. But now I am curious if you figured out another way to interpolate. Let me know if you are interested on having a tablet yourself. We can make one for you. Thanks, Tor --- In [email protected], Thomas Hruska <[EMAIL PROTECTED]> wrote: > > pakachunka wrote: > > Thank you again Thomas! > > > > Is there some text referent to "bounding boxes" I can read? Is there > > some literature to follow what you are saying? > > > > Just to make you understand better what I am doing: I am making a > > driver for a new type of low cost tablet for linux. Tablets in general > > have problems with linearization, so I am creating a way to convert > > the (u,v) voltages measured by the tablet, into (x,y) position in the > > screen. For that I need a linearization procedure, during which the > > user put the tablet stylus over marks in the screen. That is when the > > mesh of triangles mentioned before are created. After the mesh is > > ready and set, I use some Conformal Transform to transform the (u,v) > > voltages into (x,y) positions, based on the mesh. For that I need to > > determine in which triangle of the mesh the (u,v) voltages are contained. > > > > Everything needs to run in a PIC microcontroller. > > > > The tablet aims education and will be freeware. > > > > Thanks! > > > > Tor > > Quick search on Google for "bounding box" turns up: > > http://en.wikipedia.org/wiki/Minimum_bounding_rectangle > > > Why a triangle mesh though? If you collected 9 (u,v) data points from > the user (corners, midpoints, center), can't you just use linear > interpolation for the values based on those points? > > Or you could figure out a mathematical formula that applies some sort of > quadratic curve that better fits the display. Collect a whole bunch of > sample (u,v) -> (x,y) values and plug 'em into Excel and stare at and > fiddle with the numbers for a while. There are always patterns to be > found. If you can avoid the triangle mesh with a few quadratic curves, > it would, IMO, be worth the effort and generally perform well. > > Collecting data points from the user that form rectangles seems simpler > to me than building a big ol' triangle mesh. Simple typically works > better (not always the case). But, hey, I'm not an electrical engineer. > > -- > Thomas Hruska > CubicleSoft President > Ph: 517-803-4197 > > *NEW* MyTaskFocus 1.1 > Get on task. Stay on task. > > http://www.CubicleSoft.com/MyTaskFocus/ >
