xyrotate

Rotate X,Y by Theta degrees about Xo,Yo.

It seems I often want to rotate a set of points. I usually want to rotate about some point (Xo,Yo) by a certain angle expressed in units of DEGREES. The routine here does that. When I run it with no arguments it tells me useful stuff:

A positive angle rotates in a Clockwise (CW) direction
A negative angle rotates in a Counter-clockwise (CCW) direction

I often want to perform this opertaion on a list of x,y values, so I've coded the script "rotate_list" for that. These are not efficient routines from a computational point of view. If you want to transform 10^5 coordinates a hundred times, then you would use the coordinate transformation subroutines in my libraries for that! But, given the time and confusion I have expended on doing this sort of thing, these little scripts have their place.

Usage: xyrotate.sh 66.0 0.0 0.0 120.0 -450
arg1 - rotation angle in degrees (- for CCW, + for CW)  
arg2 - Xo of rotation center 
arg3 - Yo of rotation center 
arg4 - X to be transformed   
arg5 - Y to be transformed   

% xyrotate.sh 20.0 100 100 100 120 
   106.840    118.794

% xyrotate.sh -20.0 100 100 100 120
    93.160    118.794

% xyrotate.sh 20.0 100 100 120 100
   118.794     93.160

% xyrotate.sh 20.0 100 100 80 80 
    74.366     88.047

An example of running some of the above coordinates in a list form is shown below:

 
Usage: rotate_list list.1 30.0 1.0 -1.0 
arg1 - name of file with list of x,y 
arg2 - rotation angle in degrees (- for CCW, + for CW)
arg3 - x rotation center, Xo 
arg4 - y rotation center, Yo 

% cat dat.1
100.0  120.0 
120.0  100.0 
80.0   100.0
80.0  80.0 

% rotate_list dat.1 +20.0 100.0 100.0   
% rotate_list dat.1 +20.0 100.0 100.0
   106.840    118.794
   118.794     93.160
    81.206    106.840
    74.366     88.047

% rotate_list dat.1 -20.0 100.0 100.0 
    93.160    118.794
   118.794    106.840
    81.206     93.160
    88.047     74.366

Notice that in this simple example I am rotating through only a small angle. My input points are at easy locations on the unit circle, and so I can quickly verify that I have indeed rotated my points in a clockwise direction (beacues I use a POSITIVE angle).

Just to be totally anal retentive, how about a plot:

 

% head list.1
-3694.7822 4416.2168
-3247.4417 4426.0132
-2796.8501 4432.3755
-2341.5298 4445.8818
(and on to 448) 

% rotate_list list.1 3.0 0 0 > list.2
% xyrotate.py list.1 list.2 -5000 5000 -5000 5000
% display plot.png

Here, using the nice legend in the upper-right corner of my plot, I would prove to myself that I had indeed rotate the point about 0,0 by 3 degrees in a clockwise direction.

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