Re: [R] Draw text with a box surround in plot.

From: Peter Ehlers <ehlers_at_ucalgary.ca>
Date: Wed, 09 Jun 2010 16:30:29 -0600

On 2010-06-09 14:17, guox_at_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, 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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