/**
  * Center X values of the axis 
  *
  * @param awAxis $axis An axis
  * @param float $value The reference value on the axis
  */
 public function setXCenter(awAxis $axis, $value)
 {
     // Check vector angle
     if ($this->line->isVertical() === FALSE) {
         trigger_error("setXCenter() can only be used on vertical axes", E_USER_ERROR);
     }
     $p = $axis->getPointFromValue($value);
     $this->line->setX($p->x, $p->x);
 }
 /**
  * Center X values of the axis
  *
  * @param awAxis $axis An axis
  * @param float $value The reference value on the axis
  */
 public function setXCenter(awAxis $axis, $value)
 {
     // Check vector angle
     if ($this->line->isVertical() === FALSE) {
         awImage::drawError("Class Axis: setXCenter() can only be used on vertical axes.");
     }
     $p = $axis->getPointFromValue($value);
     $this->line->setX($p->x, $p->x);
 }