Glossary¶
This glossary uses NautiPy’s conventions. Follow the links for longer explanations and scientific context.
Accuracy¶
How closely a measurement agrees with the value of interest. Accuracy is not created by printing more digits. Compare precision.
Ambiguity¶
A situation in which materially different positions satisfy the available syntax or observations. NautiPy reports ambiguity instead of silently choosing one interpretation. See coordinate order and two-range geometry.
Antimeridian¶
The longitude-numbering seam at 180° east/west. A short geodesic may cross it normally. Wikipedia overview.
Azimuth / bearing¶
An angular direction. In NautiPy, bearings are true degrees clockwise from
north and generated values are normalized to [0, 360).
Azimuth background.
Bearing observation¶
A true initial bearing measured at the unknown position toward a known reference, in degrees. Its required uncertainty is one standard deviation in degrees.
Candidate¶
A mathematical position satisfying an exact two-bearing or two-range construction. A candidate may still have weak or rank-deficient geometry and is not automatically a successful general fix.
Condition number¶
A local measure of how unevenly the observations constrain different directions. Large values indicate sensitivity and weak geometry. Background.
Confidence ellipse¶
NautiPy’s local, linearized 95% position-uncertainty region, summarized by semi-major and semi-minor axes and a major-axis true bearing. It is not a safety boundary. See the uncertainty guide.
Coordinate order¶
Whether a pair is interpreted as latitude/longitude or longitude/latitude.
NautiPy defaults ordinary unmarked input to latlon; GeoJSON Points use their
specified lonlat order.
Covariance¶
A matrix describing local east/north variances and their co-variation. NautiPy reports it in square metres for a suitable converged fix. Background.
DD¶
Decimal degrees, such as 50.122570, 8.665700.
DDM¶
Degrees and decimal minutes, such as
50° 7.3542′ N; 8° 39.9420′ E. dmm is accepted as an alias.
Degrees of freedom¶
For a fix with n scalar observations and two fitted local coordinates, NautiPy reports n − 2. Reduced chi-square is available only when this is positive.
DMS¶
Degrees, minutes, and seconds, such as
50° 7′ 21.25″ N; 8° 39′ 56.52″ E.
Ellipsoid¶
A mathematically smooth, slightly flattened surface used to model Earth. NautiPy navigation uses the WGS84 reference ellipsoid rather than a sphere.
Final bearing¶
The forward azimuth on arrival while continuing along the geodesic. It is not the reciprocal direction from end back to start.
Fix¶
An estimated unknown position from known references and observed bearings, ranges, or both. NautiPy couples a fix with status and diagnostics rather than returning only coordinates.
GeoJSON¶
A JSON-based geospatial interchange format defined by RFC 7946. Its coordinate arrays use longitude, latitude order. NautiPy supports two-dimensional Points and Point FeatureCollections.
Geodesic¶
A locally straight surface path. NautiPy uses shortest WGS84 ellipsoidal geodesics for navigation and observation predictions. Background.
Initial bearing¶
The forward azimuth at the start of a geodesic.
ISO 6709¶
An international standard for representing geographic point coordinates. NautiPy accepts and emits an unambiguous signed two-dimensional subset. Standard page.
Latitude¶
Angular position north or south of the equator. NautiPy accepts values in
[-90, 90] degrees.
Longitude¶
Angular position east or west around Earth. NautiPy accepts values in
[-180, 180] degrees and never wraps invalid parser input.
NMEA coordinate fields¶
Fixed-width latitude and longitude fields accompanied by required direction fields. NautiPy reads coordinate-field pairs, not complete NMEA sentences. NMEA 0183 standard page.
Objective¶
The sum of squared standardized residuals in a fitted position fix.
Position¶
NautiPy’s immutable validated value containing finite latitude and longitude in decimal degrees, plus optional identifier and description metadata.
Precision¶
The fineness of a representation or repeatability of measurements. NautiPy can infer lexical angular resolution, but it does not treat displayed digits as measurement accuracy.
Range observation¶
A shortest WGS84 surface distance between the unknown position and a known reference, in metres. Its required uncertainty is one standard deviation in metres.
Rank¶
The number of independent local dimensions constrained by the observation Jacobian. A successful two-dimensional fix requires rank 2.
Residual¶
Prediction minus observation. Bearings use a wrapped degree difference; ranges use metres.
RMS¶
Root mean square. FixResult.rms summarizes standardized residuals and is
dimensionless; bearing and range RMS fields retain their natural units.
Standard deviation¶
A scale for uncertainty or spread. Fix observations require a positive one-standard-deviation uncertainty in degrees or metres. Background.
Standardized residual¶
A natural residual divided by its observation uncertainty. Standardization lets degree and metre observations contribute on a meaningful common scale.
True north¶
Direction along the local meridian toward the geographic North Pole, as distinct from magnetic north. NautiPy does not apply magnetic variation.
WGS84¶
The World Geodetic System 1984 reference system used by NautiPy navigation, GeoJSON point interchange, and position fixing. NGA reference material.