Nice Label Algorithm for Charts with minimum ticks

Question

I need to calculate the Ticklabels and the Tickrange for charts manually.

I know the \"standard\" algorithm for nice ticks (see http://books.google.de/books?id=fvA7

Answer 1

I found this thread while writing some php, so now the same code is available in php too!

class CNiceScale {

  private $minPoint;
  private $maxPoint;
  private $maxTicks = 10;
  private $tickSpacing;
  private $range;
  private $niceMin;
  private $niceMax;

  public function setScale($min, $max) {
    $this->minPoint = $min;
    $this->maxPoint = $max;
    $this->calculate();
  }

  private function calculate() {
    $this->range = $this->niceNum($this->maxPoint - $this->minPoint, false);
    $this->tickSpacing = $this->niceNum($this->range / ($this->maxTicks - 1), true);
    $this->niceMin = floor($this->minPoint / $this->tickSpacing) * $this->tickSpacing;
    $this->niceMax = ceil($this->maxPoint / $this->tickSpacing) * $this->tickSpacing;
  }

  private function niceNum($range, $round) {
    $exponent; /** exponent of range */
    $fraction; /** fractional part of range */
    $niceFraction; /** nice, rounded fraction */

    $exponent = floor(log10($range));
    $fraction = $range / pow(10, $exponent);

    if ($round) {
      if ($fraction < 1.5)
        $niceFraction = 1;
      else if ($fraction < 3)
        $niceFraction = 2;
      else if ($fraction < 7)
        $niceFraction = 5;
      else
        $niceFraction = 10;
    } else {
      if ($fraction <= 1)
        $niceFraction = 1;
      else if ($fraction <= 2)
        $niceFraction = 2;
      else if ($fraction <= 5)
        $niceFraction = 5;
      else
        $niceFraction = 10;
    }

    return $niceFraction * pow(10, $exponent);
  }

  public function setMinMaxPoints($minPoint, $maxPoint) {
    $this->minPoint = $minPoint;
    $this->maxPoint = $maxPoint;
    $this->calculate();
  }

  public function setMaxTicks($maxTicks) {
    $this->maxTicks = $maxTicks;
    $this->calculate();
  }

  public function getTickSpacing() {
    return $this->tickSpacing;
  }

  public function getNiceMin() {
    return $this->niceMin;
  }

  public function getNiceMax() {
    return $this->niceMax;
  }

}