Re: Perpendicular lines do not appear perpendicular
- To: mathgroup at smc.vnet.net
- Subject: [mg100310] Re: Perpendicular lines do not appear perpendicular
- From: Szabolcs Horvát <szhorvat at gmail.com>
- Date: Mon, 1 Jun 2009 07:04:17 -0400 (EDT)
- References: <gvtmhv$gh8$1@smc.vnet.net>
Bill wrote:
> Perpendicular lines do not appear perpendicular
>
> Hi:
>
> I have taken the line equation 2*x+4*y-6==0, and rotated it 90 degrees counterclockwise about {0,0},
> using a 3x3 rotation matrix.
> Here's the Mathematica 6.0.1 code that I used:
>
> rMat = {{Cos[90 Degree], - Sin[90 Degree], 0}, {Sin[90 Degree],
> Cos[90 Degree], 0}, {0, 0, 1}}
>
> l={2, 4, -6}
>
> rMat.l
>
> Output: {-4,2,-6}
>
> Placing these numbers into the general form of the equation of the line Ax+By+c=0, I get -4*x + 2*y - 6 == 0.
> Placing the 2 perpendicular line equations into ContourPlot:
>
> ContourPlot[{2*x + 4*y - 6 == 0, -4*x + 2*y - 6 == 0}, {x, -4,
> 4}, {y, -4, 4}, AspectRatio -> 1]
>
> and plotting, I notice that on my pc screen that the lines do not look perpendicular, as does the plot frame.
> Perhaps this is just my computer screen, a HP f2105. I can hold up a square cut piece of paper to the lines
> on the screen, and notice the out-of-square condition. I used AspectRatio->1, but still no joy.
>
> Question: Can someone suggest a remedy for my problem, if one exists?
>
You need AspectRatio -> Automatic, not AspectRatio -> 1 (the latter just
makes the figure a square), but for this particular plot this does not
matter (because the x and y ranges are the same). The lines are
perpendicular on my screen. Do check if your screen is operating in its
native resolution.