Description
Look up the rounded geometric GRS80 flattening and inverse flattening.
Geodesy distinguishes a mathematical reference ellipsoid, a realized coordinate datum and the physical gravity field. Geodetic latitude follows the ellipsoid normal; geocentric latitude follows a radius from the center. Ellipsoidal height, orthometric height and geoid undulation are separate signed quantities. Keep the declared ellipsoid, coordinate axes, angular units and time scale with a result.
Look up the rounded geometric GRS80 flattening and inverse flattening.
GRS80 provides a reference ellipsoid and a normal gravity model. Geometric flattening and model normal gravity are reference quantities; neither identifies a measured local gravity or a datum realization by itself.1
When to use this tool
Use this tool when you need to look up the rounded geometric GRS80 flattening and inverse flattening.
How to use the tool and how it works
- Enter ellipsoid using the definitions below.
- Run the operation. Resolve input-format errors before interpreting an output.
- Read result.flattening, result.inverseFlattening, result.reference, using the stated boundary, ordering, sign and absence conventions.
Require the exact ellipsoid string GRS80 and return rounded inverse flattening 298.257222101 with its reciprocal.2
| Input field | Meaning and units | Accepted input |
|---|---|---|
| ellipsoid | Exact supported ellipsoid identifier: GRS80. | Text, at most 8,192 UTF-16 code units; narrower grammar/range rules also apply. |
| Output field | Interpretation |
|---|---|
| result | Object containing the fields below. |
| result.flattening | Dimensionless ordinary flattening f=(a−b)/a. |
| result.inverseFlattening | Rounded dimensionless reciprocal flattening, 298.257222101 for GRS80. |
| result.reference | Name/validity note for the pinned table or rounded reference constant. |
{
"input": {
"ellipsoid": "GRS80"
},
"output": {
"result": {
"flattening": 0.003352810681182319,
"inverseFlattening": 298.257222101,
"reference": "GRS80, rounded geometric inverse flattening"
}
}
}Limitations and assumptions
- Flattening is dimensionless and differs from its inverse. This lookup does not select a datum realization, epoch, geoid or transformation parameters.
- All quantities are finite and retain the units stated for this operation. Ellipsoid-parameter tools use semi-major axis 1–10⁸ m and dimensionless flattening 0–0.02; explicit-axis tools use 0.9a≤b≤a unless a tighter bound is stated. These tools do not fetch datums, geoid grids, satellite observations or Earth-orientation updates.
- Every declared outer field is required and unknown outer fields are rejected. Strings and JSON text have size limits, lists are bounded to 128 entries, and JSON nesting/node counts are bounded. Tighter operation-specific bounds stated above take precedence.
- Numeric results must be finite. Large physical magnitudes are allowed by the output evidence checks, while integer fields and source schemas retain their exactness rules. Source indexes are zero-based. Floating-point residues can remain even where an ideal formula gives an exact zero.
Alternative or Complementary methods
Use a coordinate transform for a change of representation and explicit datum parameters for a change of reference frame. Preserve model and convergence metadata, and use observation and datum information appropriate to a real survey before interpreting a computed tolerance as accuracy.
References
-
Geodetic Reference System 1980 (corrected reference) — H. Moritz; International Association of Geodesy, hosted by MIT
-
Tool behavior and example: GRS80 Flattening Parameter Lookup — tool.io
Similar or alternative tools
- Ellipsoid Flattening from Axes Calculator f=(a-b)/a
Calculate ordinary geometric flattening from explicit oblate or spherical semiaxes.
- Third Flattening n Computation Calculator
Calculate dimensionless third flattening from explicit oblate or spherical semiaxes.