Image Rotation

TJHJ

So I have a UOled 128 display and a Uoled Prop 96, I have been plotting a series of points on the screen derived from GPS data, I store the ploted pixels into an array for X and Y. I couldnt find much searching, so here I am.
Here is the big question Can anyone think of a good method to rotate the image on the screen?

How I have been trying to do it was with float math32Full.
Take Point 1, Find L and Theta from pixel 64, 64(Middle of Screen) For L find using the Distance Forumla. ((Ox-X)^2(Oy-y)^2)^(1/2) = L then find theta ArcSin((Y-64)/L)
Now Regenerate the data points for one angle offset - X = L*Sin(Theta+Offset) Y= L*Cos(Theta+offset)

Other than it doesnt work how it should, this is aweful. So if anyone knows of an object that rotates an image, or how to do it easily it would be greatly appricated.

Thank you
TJ

·

Rayman

Image rotation can be done as a series of shifts in x and y... No need for higher math.

TJHJ

Can you elaborate? I cant seem to work out in my mind how to pull this off.

So lots of time on google I came up with this.
http://homepages.inf.ed.ac.uk/rbf/HIPR2/rotate.htm
Which defines the·rotation as the following

repeat i from 0 to TrackL
    Cx[noparse][[/noparse]i]:= F.FRound(F.Fadd(F.Fsub(F.FMul(F.Cos(F.FFloat(F.Degrees(Anglenew))),F.Fsub(Mapx[noparse][[/noparse]i],Fox)), F.FMul(F.Sin(F.FFloat(F.Degrees(Anglenew))),F.Fsub(Mapy[noparse][[/noparse]i], Foy))),Fox))
    Cy[noparse][[/noparse]i]:= F.FRound(F.Fadd(F.Fsub(F.FMul(F.Sin(F.FFloat(F.Degrees(Anglenew))),F.Fsub(Mapx[noparse][[/noparse]i],Fox)), F.FMul(F.Cos(F.FFloat(F.Degrees(Anglenew))),F.Fsub(Mapy[noparse][[/noparse]i], Foy))),Fox))
      

So I ended up with the above but Im not getting anywhere? Did I miss something obvious?

Post Edited (TJHJ) : 6/10/2008 5:05:32 AM GMT

Lord Steve

Just to clarify:· Do you want to rotate an image (bitmap)?· Or do you want to rotate the points before drawing them?

TJHJ

Im 50-50 on that, I think it would be easier to rotate the points 1st then drawn them, Becuase it actually draws lines connecting the dots.
So I have a maxium of 500 byte points, into a variable array.
Defined as so
Mapx[noparse][[/noparse]500]
Mapy[noparse][[/noparse]500]

So I would like to do it with a repeat command, but If I made it a bitmap, I think it would calc out faster when it was close to the maxium of the 500 points, but I am horriable at Bitmaps, I have a hard time keeping up with them. But IM open to learn and try anything.
·

Leon

Standard techniques are quaternions and rotation matrices, if you need high performance.

Leon

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Rayman

TJHJ said...
Can you elaborate? I cant seem to work out in my mind how to pull this off.

Look here (for example):

http://www.leptonica.com/rotation.html

under "rotation by shear".

This is the fast way to rotate images.

VIRAND

I don't have code handy but I see what you are doing and you are very close to making it work well.

Basically your rotation method is converting to polar coordinates
and then after that conversion you can plot any angle of rotation you want with your method to
"Regenerate your data points".

There is a missing + in your distance formula and another problem is that you are losing your
quadrant information (X and Y offset signs +/-) with the distance formula and the theta formula.
Maybe you need an arccos also. Without the lost information you can only rotate points from
one fourth of the screen.

Don D

TJHJ
No need to repeat the sin and cos functions for every point in the loop. Calculate as much as you can outside the loop and use them as constants inside the loop.

Paul Baker

Another method is by using cordic:

http://forums.parallax.com/showthread.php?p=609053

http://forums.parallax.com/showthread.php?p=642142


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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

rjo_

TJ

Is this a fixed angle or a variable angle?

Rich