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

[Peter Ehlers]

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
>>
>>