How about a R-Tree? How costly is that?
--- In [email protected], "pakachunka" <[EMAIL PROTECTED]> wrote: > > I said Linear Regression. Actually, the guy is using least squares, > since we are trying to fit a quadratic function. The difficult part > is that it is a R2->R2 function, that is, (u,v)->(x,y) > > But I still want to seek a solution based on the mesh triangles > mentioned before, since I believe fitting quadratic curves may be > good for one side of the table, but not good for other parts. > > Thanks! > > --- In [email protected], "pakachunka" <pakachunka@> wrote: > > > > 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 <thruska@> 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/ > > > > > >
