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

guox at ucalgary.ca guox at ucalgary.ca
Thu Jun 10 00:57:50 CEST 2010

```For me, the angles circled are not exactly right.
See the pdf file: plot.pdf.
But it is OK.
-james
> 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.
>>>>>> 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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