Calculator Reference

This page documents every Calculator class available for the Bulk Propagation API.

Each calculator represents an output that can be computed in WASM. You pick only the calculators you need: less work means faster runs. Calculators have dependencies - if a calculator requires another one, both must be present in the calculators array passed to BulkPropagator.

tip

Outputs are packed in TypedArray buffers, and indices are always sorted satellite-first, date-second: index = satelliteIndex * datesCount + dateIndex.

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EciBaseCalculator

Runs SGP4 propagation and produces ECI position and velocity vectors. This is the WASM equivalent of the pure JS propagate(). As the base of calculations, it must be always present.

Property	Value
Key in the output	eci
Dependencies	none
Run parameters	none
Formatted output	{ position: EciVec3<Kilometer>, velocity: EciVec3<KilometerPerSecond>, error: SatRecError }
Raw output	{ position: Float64Array, velocity: Float64Array, error: Int8Array }

Raw data layout:

• position - [x₀, y₀, z₀, x₁, y₁, z₁, …] for each satellite/date pair
• velocity - [vx₀, vy₀, vz₀, vx₁, vy₁, vz₁, …] for each satellite/date pair
• error - [err₀, err₁, …] - SatRecError value for each pair

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GmstCalculator

Calculates Greenwich Mean Sidereal Time, needed by coordinate-transform calculators. WASM equivalent of gstime().

Property	Value
Key in the output	gmst
Dependencies	none
Run parameters	none
Formatted output	GMSTime
Raw output	Float64Array

Raw data layout: [gmst₀, gmst₁, …] - one value per date (not duplicated per satellite).

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EcfPositionCalculator

ECF (Earth-Centered Fixed) position. WASM equivalent of eciToEcf() applied to position.

Property	Value
Key in the output	ecfPosition
Dependencies	eci, gmst
Run parameters	none
Formatted output	EcfVec3<Kilometer>
Raw output	Float64Array

Raw data layout: [x₀, y₀, z₀, x₁, y₁, z₁, …] for each satellite/date pair.

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EcfVelocityCalculator

ECF velocity. WASM equivalent of eciToEcf() applied to velocity.

Property	Value
Key in the output	ecfVelocity
Dependencies	eci, gmst
Run parameters	none
Formatted output	EcfVec3<KilometerPerSecond>
Raw output	Float64Array

Raw data layout: [vx₀, vy₀, vz₀, vx₁, vy₁, vz₁, …] for each satellite/date pair.

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GeodeticPositionCalculator

Geodetic position (latitude, longitude, height). WASM equivalent of eciToGeodetic().

Property	Value
Key in the output	geodeticPosition
Dependencies	eci, gmst
Run parameters	none
Formatted output	GeodeticLocation object: { latitude, longitude, height }
Raw output	Float64Array

Raw data layout: [lat₀, lon₀, h₀, lat₁, lon₁, h₁, …] for each satellite/date pair.

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LookAnglesCalculator

Look Angles (azimuth, elevation, range). WASM equivalent of ecfToLookAngles().

Requires observer geodetic coordinates at run time.

Property	Value
Key in the output	lookAngles
Dependencies	ecfPosition
Run parameters	{ observer: GeodeticLocation } - { latitude, longitude, height } in radians and km
Formatted output	LookAngles object: { azimuth, elevation, rangeSat }
Raw output	Float64Array

Raw data layout: [az₀, el₀, range₀, az₁, el₁, range₁, …] for each satellite/date pair.

Run-time usage:

bulkPropagator.run({
  dates,
  lookAngles: {
    observer: {
      latitude: degreesToRadians(41),
      longitude: degreesToRadians(-71),
      height: 0.1,
    },
  },
});

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DopplerFactorCalculator

Doppler factor. WASM equivalent of dopplerFactor().

Requires observer ECF coordinates at run time.

Property	Value
Key in the output	dopplerFactor
Dependencies	ecfPosition, ecfVelocity
Run parameters	{ observer: EcfVec3<Kilometer> } - { x, y, z } in km
Formatted output	number
Raw output	Float64Array

Raw data layout: [df₀, df₁, …] for each satellite/date pair.

Run-time usage:

const observerGeodetic = {
  latitude: degreesToRadians(41),
  longitude: degreesToRadians(-71),
  height: 0.1,
};

bulkPropagator.run({
  dates,
  dopplerFactor: {
    observer: geodeticToEcf(observerGeodetic),
  },
});

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SunPositionCalculator

Sun position in the equatorial ECI frame, in AU. WASM equivalent of sunPos().

Property	Value
Key in the output	sunPosition
Dependencies	none
Run parameters	none
Formatted output	EciVec3<AU>
Raw output	Float64Array

Raw data layout: [x₀, y₀, z₀, x₁, y₁, z₁, …] - one vector per date (not duplicated per satellite).

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ShadowFractionCalculator

Fraction of the Sun's disc obscured by the Earth. WASM equivalent of shadowFraction().

Property	Value
Key in the output	shadowFraction
Dependencies	eci, sunPosition
Run parameters	none
Formatted output	number - 0 = fully lit, 1 = umbra, 0–1 = penumbra
Raw output	Float64Array

Raw data layout: [sf₀, sf₁, …] for each satellite/date pair.