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The Calculate Max Elevation Figures tool computes the maximum elevation figures for an Operational Navigation Chart (ONC) based on the type of the highest vertical obstruction in a quadrangle. Two obstruction types influence the calculation: human-made and natural terrain. The calculation differs if one type is higher than the other or if the obstruction is below sea level.
Human-made vertical obstruction
If the highest vertical obstruction within a quadrangle is a human-made feature, the Calculate Max Elevation Figures tool follows this process:
- Determine the elevation of the top of the feature above mean sea level (MSL).
- Add the vertical error figure (vertical accuracy factor of data/source).
- Round the resultant sum to the next higher 100-foot level for the final figure.
Hinweis:
A resultant figure is not rounded up to the next higher 100-foot level when it is an even multiple of 100.
Example
Elevation of vertical obstruction (top, above mean sea level) = 6,265 ft. Possible vertical error = + 500 ft. Sum elevation and vertical error = 6,765 ft. Round to next higher 100 ft. level = 6,800 ft. Maximum Elevation Figure (MEF) = 68
Natural terrain feature vertical obstruction
If the highest vertical obstruction within a quadrangle is a natural terrain elevation, the Calculate Max Elevation Figures tool follows this process:
- Determine the highest natural terrain elevation.
- Add an allowance of 61 meters (200 feet) for nonrepresented natural or human-made features.
- Add the vertical error figure (vertical accuracy factor of data/source).
- Round the resultant sum to the next higher 100-foot level for the final figure.
Hinweis:
A resultant figure is not rounded up to the next higher 100-foot level when it is an even multiple of 100.
Example
Highest natural terrain elevation (above mean sea level) = 9,815 ft. Allowance = 200 ft. Possible vertical error = + 500 ft. Sum elevation, allowance, and vertical error = 10,515 ft. Round to next higher 100 ft. level = 10,600 ft. Maximum Elevation Figure (MEF) = 106
Highest feature is below sea level
If the highest vertical obstruction within a quadrangle is below sea level (BSL), the Calculate Max Elevation Figures tool follows this process:
- Add the BSL value to the 61-meter (200-foot) allowance for nonrepresented natural or human-made features.
- Add the vertical error figure (vertical accuracy factor of data/source).
- Round the resultant sum to the next higher 100-foot level for the final figure.
Hinweis:
A resultant figure is not rounded up to the next higher 100-foot level when it is an even multiple of 100.
Example
Highest terrain elevation (above mean sea level) = - 360 ft. Allowance = 200 ft. Possible vertical error = + 500 ft. Sum elevation, allowance, vertical error = 340 ft. Even hundred - Do not round = 300 ft. Maximum Elevation Figure (MEF) = 03