Skip to main content

Calculate the MEF for an ONC

Доступно с лицензией Production Mapping.

The Calculate Max Elevation Figures tool computes the maximum elevation figures for an Operational Navigation Chart (ONC) based on the highest vertical obstruction type in a quadrangle. Human-made and natural terrain obstructions, and features below sea level, can impact the calculation method.

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:

  1. Determine the elevation of the top of the feature above mean sea level (MSL).

  2. Add the vertical error figure (vertical accuracy factor of data/source).

  3. Round the resultant sum to the next higher 100-foot level for the final figure.

Примечание:

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)                                 =    6<sup>8</sup>

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:

  1. Determine the highest natural terrain elevation.

  2. Add an allowance of 61 meters (200 feet) for nonrepresented natural or human-made features.

  3. Add the vertical error figure (vertical accuracy factor of data/source).

  4. Round the resultant sum to the next higher 100-foot level for the final figure.

Примечание:

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)                                 =       10<sup>6</sup>

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:

  1. Add the BSL value to the 61-meter (200-foot) allowance for nonrepresented natural or human-made features.

  2. Add the vertical error figure (vertical accuracy factor of data/source).

  3. Round the resultant sum to the next higher 100-foot level for the final figure.

Примечание:

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)                                 =     0<sup>3</sup>