Grid to Coordinates / Coordinates to Grid

grid.php

<?php

// 10 pixel per grid
define('IMAGE_WH', 25); // Pixels
define('SQUARE_RC', 5); // Columns/Rows
define('IMAGE_SQ_RATIO', IMAGE_WH / SQUARE_RC); //10

function cellToCoords($cell) {
  $x = (($cell - 1) % SQUARE_RC) + 1;
  $y = ceil($cell / SQUARE_RC);

  $x *= IMAGE_SQ_RATIO;
  $y *= IMAGE_SQ_RATIO;

  // CENTER CELL: cell 1 = 5,5
  // $x -= IMAGE_SQ_RATIO / 2;
  // $y -= IMAGE_SQ_RATIO / 2;
  // $r = [$x, $y];

  // BOTTOM RIGHT: cell 1 = 10,10
  $r = [$x, $y];

  // TOP LEFT: cell 1 = 0,0
  // $x -= IMAGE_SQ_RATIO;
  // $y -= IMAGE_SQ_RATIO;
  // $r = [$x - 10, $y - 10];

  return ($r);
}

function coordsToGrid($x, $y) {
  $calcX = $x / IMAGE_SQ_RATIO;
  $calcY = (($y - IMAGE_SQ_RATIO) % SQUARE_RC) * SQUARE_RC;
  return ($calcX + $calcY);
}







/// tests

$res = [];
$res['tests'] = range(1, SQUARE_RC);
foreach ($res['tests'] as $cell) {
  $coords = cellToCoords($cell);
  $res['image_coords'][$cell] = $coords;
  $res['grid_numbers'][implode('-', $coords)] = coordsToGrid($coords[0], $coords[1]);
}

echo '<pre>';
print_r($res);
echo '</pre>';


?>

Array
(
    [tests] => Array
        (
            [0] => 1
            [1] => 2
            [2] => 3
            [3] => 4
            [4] => 5
        )

    [image_coords] => Array
        (
            [1] => Array
                (
                    [0] => 5
                    [1] => 5
                )

            [2] => Array
                (
                    [0] => 10
                    [1] => 5
                )

            [3] => Array
                (
                    [0] => 15
                    [1] => 5
                )

            [4] => Array
                (
                    [0] => 20
                    [1] => 5
                )

            [5] => Array
                (
                    [0] => 25
                    [1] => 5
                )

        )

    [grid_numbers] => Array
        (
            [5-5] => 1
            [10-5] => 2
            [15-5] => 3
            [20-5] => 4
            [25-5] => 5
        )

)

Regarding: Question 64401247
This is for a 10 pixel grid square, just divide coordinates by 10