Need help tracking pixel location with GD imagerotate

[Andy-H]

Hi, what I want to do is select a point on an image and calculate that point after incremental rotations of 1 degree until the image has done a full 360 rotation. This if for custom markers for google maps but I havent got a clue where to start. I did find some information from another popular coding help forum but don't want to post it here because of advertising but basically it said:

 

 

Yep, fairly. To map the point (x1,y1) via rotation around the origin:
x2 = cos(a) * x1 + sin(a) * y1; y2 = cos(a) * y1 - sin(a) * x1; ... so you just first need to translate to the origin i.e. (-50,-50) in your example and translate back after rotation.
x2 = cos(a) * (x1 - 50) + sin(a) * (y1 - 50) + 50; y2 = cos(a) * (y1 - 50) - sin(a) * (x1 - 50) + 50; ... Or something like that. (You can generate a matrix which will do all three transformations, I'll leave that for another answer or as an exercise...)

 

But I have no clue what the guy is talking about lol

Any help appreciated.

[btherl]

Which parts of that do you understand?  Eg do you know how cos and sin work?

 

Also are you rotating around (0,0) or are you rotating around an arbitrary point such as (50,50)?  Such as when an image is indexed from 0-100 on each axis and you want to rotate around the center of the image?

[Andy-H]

Its ok, I figured it out using these and setting a radius,

 

 

function getPoints($deg, $rad, $offsetx, $offsety)
{
    $x = round(cos($deg * M_PI / 180) * $rad) + $offsetx;
    $y = round(sin($deg * M_PI / 180) * $rad) + $offsety;


    return array('x' => $x, 'y' => $y);
}
function getCenter(&$im, $deg, $rad)
{
    $cx   = floor(imagesx($im) / 2);
    $cy   = floor(imagesy($im) / 2);
    return getPoints(($deg - 90), $rad, $cx, $cy);
    
}

 

 

Cheers