For me, the angles circled are not exactly right. See the pdf file: plot.pdf. But it is OK. Thanks Peter for your directions -james > On 2010-06-09 14:17, g...@ucalgary.ca wrote: >> Thank. >> Better. Seems that angles are close to but not equal to pi/2. >> It may be because the plot box is not a square: the length of >> x-axis is not the same as the length of y-axis. >> Even curves y = x and y = 1-x look like not orthogonal but >> they should since multiplication of their slopes is -1. >> -james > > > I disagree. Your eyes may be fooling you. Setting asp=1 ensures > that intervals (x1,x2)=(a,b) and (y1,y2)=(a,b) are of equal > length on the plot. (This seems to hold even if you resize > the plot after drawing.) > > Try removing the box around the plot: > > plot(0:30, 0:30, type='n', asp=1, axes=FALSE, xlab="", ylab="") > abline(v=c(0,30), h=c(0,30)) > abline(a=0, b=1, col=2) > abline(a=30, b=-1, col=4) > polygon(c(x1,x2,x3,x4), c(y1,y2,y3,y4), border="blue", lwd=2) > polygon(x.rotated, y.rotated, border="red", lwd=2) > > Works for me. > > -Peter Ehlers > > >> plot(1:30,1:30,xlim=c(1,30),ylim=c(1,30),type="n", main = "Rotated >> rectangle looks like a parallelogram", asp=1) >> ## a rect at (10,20) with w = 3 and h = 2 >> x = 10 >> y = 20 >> w = 3 >> h = 2 >> x1=x-w >> y1=y-h >> x2=x+w >> y2=y-h >> x3=x+w >> y3=y+h >> x4=x-w >> y4=y+h >> polygon(c(x1,x2,x3,x4),c(y1,y2,y3,y4),border="blue") >> >> ##Rotate it at (10,20) by 45 degree >> theta = 45/180*pi >> x.rotated = c(10 + (x1-10)*cos(theta)-(y1-20)*sin(theta), >> 10 + (x2-10)*cos(theta)-(y2-20)*sin(theta), >> 10 + (x3-10)*cos(theta)-(y3-20)*sin(theta), >> 10 + (x4-10)*cos(theta)-(y4-20)*sin(theta)) >> y.rotated = c(20 + (x1-10)*sin(theta)+(y1-20)*cos(theta), >> 20 + (x2-10)*sin(theta)+(y2-20)*cos(theta), >> 20 + (x3-10)*sin(theta)+(y3-20)*cos(theta), >> 20 + (x4-10)*sin(theta)+(y4-20)*cos(theta)) >> >> polygon(x.rotated,y.rotated,border="red") >> >>> Your transformation assumes that the x- and y-axes are on the >>> same scale. Add 'asp = 1' to your plot() call to set the >>> appropriate aspect ratio. >>> >>> -Peter Ehlers >>> >>> >>> On 2010-06-09 10:13, g...@ucalgary.ca wrote: >>>> Rectangle R centered at (x,y) with width 2w and height 2h is given by >>>> >>>> x1=x-w >>>> y1=y-h >>>> x2=x+w >>>> y2=y-h >>>> x3=x+w >>>> y3=y+h >>>> x4=x-w >>>> y4=y+h >>>> polygon(c(x1,x2,x3,x4),c(y1,y2,y3,y4)) >>>> >>>> Rotating a point (u,v) at (0,0) by theta degree is given by matrix >>>> [cos(theta),-sin(theta) >>>> sin(theta),cos(theta)] >>>> so we have a new point >>>> (u*cos(theta)-v*sin(theta),u*sin(theta)+v*cos(theta)). >>>> >>>> Hence rotated R by theta at (x,y) is given by >>>> >>>> x.rotated = c(x + (x1-x)*cos(theta)-(y1-y)*sin(theta), >>>> x + (x2-x)*cos(theta)-(y2-y)*sin(theta), >>>> x + (x3-x)*cos(theta)-(y3-y)*sin(theta), >>>> x + (x4-x)*cos(theta)-(y4-y)*sin(theta)) >>>> y.rotated = c(y + (x1-x)*sin(theta)+(y1-y)*cos(theta), >>>> y + (x2-x)*sin(theta)+(y2-y)*cos(theta), >>>> y + (x3-x)*sin(theta)+(y3-y)*cos(theta), >>>> y + (x4-x)*sin(theta)+(y4-y)*cos(theta)) >>>> >>>> polygon(x.rotated,y.rotated) >>>> >>>> But it turns out to be a parallelogram with angles not equal to 90, >>>> not a rectangle. See R code below. >>>> >>>> Any way to improve this so that the rotated rectangle looks like a >>>> rectangle? Thanks, >>>> >>>> -james >>>> >>>> >>>> plot(1:10,1:10,xlim=c(1,20),ylim=c(1,40),type="n", main = "Rotated >>>> rectangle looks like a ") >>>> ## a rect at (10,20) with w = 3 and h = 2 >>>> x = 10 >>>> y = 20 >>>> w = 3 >>>> h = 2 >>>> x1=x-w >>>> y1=y-h >>>> x2=x+w >>>> y2=y-h >>>> x3=x+w >>>> y3=y+h >>>> x4=x-w >>>> y4=y+h >>>> polygon(c(x1,x2,x3,x4),c(y1,y2,y3,y4),border="blue") >>>> >>>> ##Rotate it at (10,10) by 45 degree >>>> theta = 45/180*pi >>>> x.rotated = c(10 + (x1-10)*cos(theta)-(y1-20)*sin(theta), >>>> 10 + (x2-10)*cos(theta)-(y2-20)*sin(theta), >>>> 10 + (x3-10)*cos(theta)-(y3-20)*sin(theta), >>>> 10 + (x4-10)*cos(theta)-(y4-20)*sin(theta)) >>>> y.rotated = c(20 + (x1-10)*sin(theta)+(y1-20)*cos(theta), >>>> 20 + (x2-10)*sin(theta)+(y2-20)*cos(theta), >>>> 20 + (x3-10)*sin(theta)+(y3-20)*cos(theta), >>>> 20 + (x4-10)*sin(theta)+(y4-20)*cos(theta)) >>>> >>>> polygon(x.rotated,y.rotated,border="red") >>>> >>>> >>>>> On 06/04/2010 01:21 AM, g...@ucalgary.ca wrote: >>>>>> boxed.labels draw text with box well. >>>>>> But, the box cannot be shadowed and srt = 45 seems not to work: >>>>>> text is rotated but the box does not. >>>>>> polygon.shadow can rotate and shadow but have to calculate its >>>>>> dimensions, >>>>>> based on the text length and size. >>>>>> Do you have any other way to draw text with rotated and shadowed >>>>>> box? >>>>> >>>>> The srt argument was intended to allow the user to rotate the text >>>>> in >>>>> 90 >>>>> degree increments, and the box just changes shape to fit whatever is >>>>> in >>>>> it. The underlying function that draws the box (rect) doesn't have a >>>>> rotation argument. It would be possible to write a special function >>>>> using polygon, just do the calculations for box size and then rotate >>>>> the >>>>> text with srt= and the polygon by transforming the coordinates of >>>>> the >>>>> vertices, as long as the default justification (center) is used. I >>>>> can't >>>>> do this right at the moment, but if you are really stuck I might be >>>>> able >>>>> to do it in the near future. >>>>> >>>>> Jim >>>>> >>>>> > > >
plot.pdf
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