From: <guox_at_ucalgary.ca>

Date: Wed, 09 Jun 2010 14:17:12 -0600 (MDT)

polygon(c(x1,x2,x3,x4),c(y1,y2,y3,y4),border="blue")

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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Wed 09 Jun 2010 - 20:20:16 GMT

Date: Wed, 09 Jun 2010 14:17:12 -0600 (MDT)

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

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, guox_at_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, guox_at_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
**>>>
**>>>
**>
**>
**>
*

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