code: public function getElevation($latitude, $longitude)
      {
          if ($latitude === 0.0 && $longitude === 0.0) {
              return false;
          }
  
          if (!$this->locationIsInBounds($latitude, $longitude)) {
              throw new InvalidArgumentException(
                  sprintf('Location (%f, %f) is out of bounds ([-%f, %f], [-%f, %f]).',
                      $latitude, $longitude,
                      static::MAX_LATITUDE, static::MAX_LATITUDE,
                      static::MAX_LONGITUDE, static::MAX_LONGITUDE
                  )
              );
          }
  
          $filename = $this->getFilenameFor($latitude, $longitude);
  
          if ($this->CurrentFilename !== $filename) {
              $this->openResource($filename);
          }
  
          return $this->getElevationFromResource($latitude, $longitude);
      }
docs: Get elevation for specified location.
  
  Availability of data must be checked in advance via hasDataFor($locations).
  Only 'invalid' locations such as (0.0, 0.0) won't throw an exception but return false.
  
  @param  float                     $latitude
  @param  float                     $longitude
  @return int|bool                  elevation [m] can be false if nothing retrieved
  @throws InvalidArgumentException;