GELE Geodesy — Satellite Geodesy and GNSSCheat Sheet

Formula

ρ = c × Δt

Meaning

ρ = pseudorange (m); c = speed of light (299,792,458 m/s); Δt = signal travel time (s)

Watch Out

Δt is in SECONDS, not milliseconds. Common error: forgetting c is ~3×10⁸ m/s exactly (use 299,792,458 m/s for precision)

When To Use

Calculate pseudorange from satellite signal travel time; fundamental to all GNSS positioning

Formula

X = X_sat + c × (Δt_sat - Δt_receiver)

Meaning

Solve receiver position (X, Y, Z) and clock bias using satellite ephemeris and pseudorange measurements

Watch Out

Four unknowns (X, Y, Z, Δt_receiver) require MINIMUM 4 satellites; three satellites cannot solve a 3-D fix

When To Use

Conceptual formulation of trilateration with clock bias correction

Formula

n_min = 4

Meaning

Minimum number of satellites for 3-D positioning with clock bias correction

Watch Out

Three satellites give only 2-D fix (height constrained). The fourth unknown is RECEIVER CLOCK BIAS, not a satellite

When To Use

Any exam question asking 'how many satellites do you need for a 3-D fix?'

Value

299,792,458 m/s (≈ 3×10⁸ m/s)

Symbol

c

Quantity

Speed of light

Value

~20,200 km (semi-major axis a ≈ 26,560 km)

Symbol

h_GPS

Quantity

GPS orbital altitude

Value

~0.067 s (to ground from geosynchronous altitude)

Symbol

Δt_GPS

Quantity

Signal travel time (GPS)

Value

4

Symbol

n_min

Quantity

Minimum satellites for 3-D fix

Term

Pseudorange

Example

If signal takes 0.067 s, pseudorange ≈ 20,086 km (consistent with GPS orbital altitude ~20,200 km)

Definition

Range measured by multiplying receiver clock time difference by the speed of light; called 'pseudo' because receiver clock is not synchronized with satellite atomic clock.

Term

Trilateration

Example

In 2-D: three circles intersect at a point; in 3-D with clock bias: four spheres intersect at a unique point

Definition

Geometric method of determining position by measuring distances from three or more known reference points (satellites).

Term

Receiver Clock Bias (Δt_receiver)

Example

Even with inexpensive quartz clocks, this bias (typically microseconds) translates to hundreds of metres of range error without correction

Definition

The systematic error in the receiver's internal clock relative to satellite atomic time; solved as a fourth unknown in GNSS positioning.

Term

Ephemeris

Example

GPS satellites broadcast their own ephemeris data every 2 hours; used to compute X_sat, Y_sat, Z_sat

Definition

Precise 3-D position and velocity of each satellite at a given time; broadcast by the satellite and must be known for positioning calculations.

Formula

ρ_pseudorange = c × Δt

Meaning

Pseudorange (m); speed of light c; signal travel time Δt (s)

Watch Out

Pseudorange is COARSE (~1 m noise) because it depends on receiver clock accuracy; not suitable for precise work alone

When To Use

Single-frequency pseudorange positioning; DGPS and standard GPS receivers

Formula

Φ_carrier = (f/c) × ρ + N × λ + errors

Meaning

Φ = carrier phase (cycles); f = frequency; ρ = true range; N = integer ambiguity (cycles); λ = wavelength (m)

Watch Out

Ambiguity N is UNKNOWN integer; must be resolved (fixed) to use carrier phase. This is the bottleneck of precise GNSS

When To Use

Precise GNSS positioning (geodetic surveys, RTK); carrier-phase observables

Formula

λ = c / f

Meaning

Wavelength (m); c = speed of light; f = frequency (Hz)

Watch Out

GPS L1 = 1575.42 MHz → λ_L1 ≈ 0.19 m; L2 = 1227.60 MHz → λ_L2 ≈ 0.24 m

When To Use

Relate frequency to wavelength for L-band GNSS frequencies

Formula

Precision = λ / N_observable

Meaning

Carrier phase precision (m); wavelength λ; cycling ambiguity N

Watch Out

Carrier phase is PRECISE but AMBIGUOUS; pseudorange is COARSE but UNAMBIGUOUS

When To Use

Compare pseudorange (~1 m) vs carrier phase (~mm) accuracy

Value

1575.42 MHz

Symbol

f_L1

Quantity

GPS L1 frequency

Value

0.1905 m ≈ 19.05 cm

Symbol

λ_L1

Quantity

GPS L1 wavelength

Value

1227.60 MHz

Symbol

f_L2

Quantity

GPS L2 frequency

Value

0.2442 m ≈ 24.42 cm

Symbol

λ_L2

Quantity

GPS L2 wavelength

Value

1–5 m (1-σ)

Symbol

σ_pseudorange

Quantity

Pseudorange noise (typical)

Value

2–5 mm (1-σ)

Symbol

σ_phase

Quantity

Carrier phase noise (typical)

Term

Carrier Phase Observable

Example

GPS L1 carrier phase at 1575.42 MHz (λ ≈ 0.19 m); one cycle = 0.19 m of range

Definition

Count of whole wavelengths plus fractional phase from satellite to receiver; precision ~mm but requires integer ambiguity resolution.

Term

Integer Ambiguity (N)

Example

With 4 satellites × 2 frequencies, solve 8 ambiguities; fixing these reduces error from metres to centimetres

Definition

Unknown number of complete wavelengths between satellite and receiver at the start of tracking; resolved in post-processing or real-time via RTK.

Term

Dual-Frequency GNSS

Example

Single-frequency: ambiguity fixing takes minutes; dual-frequency: seconds to minutes

Definition

Receiver tracking two frequencies (e.g., GPS L1 and L2) to remove ionospheric delay and resolve ambiguities faster.

Formula

Total Error = Clock Error + Orbit Error + Iono Delay + Tropo Delay + Multipath + Receiver Noise

Meaning

All systematic and random errors contribute to pseudorange/phase bias

Watch Out

Errors are NOT always additive; correlations (especially between iono and tropo) exist

When To Use

Understand error budget and why differential GNSS removes common errors

Formula

Iono Delay = 40.3 × (TEC / f²)

Meaning

TEC = Total Electron Content (electrons/m²); f = frequency (Hz); delay in metres

Watch Out

Single-frequency receivers see ~5–50 m error on L1 alone; dual-frequency reduces this to ~0.1 m

When To Use

Explain why dual-frequency receivers form ionosphere-free combinations

Formula

Tropo Delay ≈ 2.5 m at zenith (dry component)

Meaning

Depends on temperature, pressure, humidity; increases with lower elevation angle

Watch Out

Tropo is FREQUENCY-INDEPENDENT (same for L1 and L2); cannot remove by dual-frequency like iono

When To Use

Estimate systematic delay for low-elevation satellites; corrected using models (Hopfield, Saastamoinen)

Value

~1 m

Symbol

δt_sat

Quantity

Satellite clock error (uncorrected)

Value

2–5 m

Symbol

δr_orbit

Quantity

Orbit error (broadcast ephemeris)

Value

5–50 m (varies by time of day, solar activity)

Symbol

δ_iono

Quantity

Ionospheric delay (L1, zenith)

Value

2.5 m (dry) + 0.1–0.5 m (wet)

Symbol

δ_tropo

Quantity

Tropospheric delay (zenith)

Value

1–3 m

Symbol

δ_MP_code

Quantity

Multipath (pseudorange)

Value

5–50 mm

Symbol

δ_MP_phase

Quantity

Multipath (carrier phase)

Term

Ionospheric Delay

Example

L1 (1575 MHz) sees more delay than L2 (1227 MHz); difference used to estimate and remove iono effects

Definition

Propagation delay caused by free electrons in the ionosphere; frequency-dependent, causing code/phase distortion on different frequencies.

Term

Tropospheric Delay

Example

~2.5 m at zenith; increases to ~20 m for 5° elevation angle

Definition

Propagation delay in the neutral atmosphere (troposphere); frequency-independent, caused by dry gases and water vapor.

Term

Multipath

Example

GPS receiver near building or water surface sees multipath; solution: use choke-ring antenna or move away from reflectors

Definition

Signal reflected off nearby objects before reaching antenna; creates phase distortion and range bias.

Term

Cycle Slip

Example

Typical during low elevation, obstructed sky, or receiver motion; must be detected and repaired

Definition

Loss of phase lock on satellite signal, causing discontinuity in carrier-phase count (integer ambiguity jumps by N cycles).

Term

Satellite Geometry (DOP)

Example

Satellites spread across sky → low DOP → high accuracy; satellites clustered overhead → high DOP → poor accuracy

Definition

Quality of spatial distribution of satellites; quantified by Dilution of Precision (DOP); lower DOP = better geometry.

Formula

Accuracy ≈ DOP × σ_measurement

Meaning

Accuracy (m); DOP = dimensionless geometry factor; σ = user-equivalent range error (UERE) or noise (m)

Watch Out

DOP is GEOMETRIC ONLY; does not include systematic errors (iono, tropo, orbit); this formula gives PRECISION, not ACCURACY

When To Use

Estimate positioning uncertainty from satellite geometry and receiver noise

Formula

PDOP = √(σ_X² + σ_Y² + σ_Z²)

Meaning

Position DOP; combines 3-D position uncertainty

Watch Out

PDOP includes clock uncertainty; cannot isolate horizontal/vertical separately

When To Use

Overall accuracy estimate including all coordinates

Formula

HDOP = √(σ_X² + σ_Y²)

Meaning

Horizontal DOP; includes only X and Y (horizontal plane)

Watch Out

HDOP alone does NOT tell you Z error; use VDOP for vertical or PDOP for total

When To Use

Estimate horizontal accuracy (useful for navigation, surveying horizontal control)

Formula

VDOP = σ_Z

Meaning

Vertical DOP; includes only Z (height)

Watch Out

VDOP is typically 1.5–3 times larger than HDOP due to poor vertical satellite geometry

When To Use

Estimate vertical (height) accuracy

Formula

UERE ≈ 5 m (typical single-frequency GPS, standard code)

Meaning

User Equivalent Range Error; combined pseudorange noise including all unmodelled errors

Watch Out

Can increase to 10+ m in poor conditions (low elevation, high humidity, solar activity)

When To Use

Default estimate if no other information given; scales with elevation mask and atmospheric conditions

Value

< 4

Symbol

PDOP_excellent

Quantity

Excellent PDOP

Value

4–8

Symbol

PDOP_good

Quantity

Good PDOP

Value

8–16

Symbol

PDOP_moderate

Quantity

Moderate PDOP

Value

> 16

Symbol

PDOP_poor

Quantity

Poor PDOP

Value

1–2

Symbol

HDOP_typical

Quantity

Typical HDOP (open sky)

Value

2–4

Symbol

VDOP_typical

Quantity

Typical VDOP (open sky)

Value

5 m (1-σ)

Symbol

UERE

Quantity

Standard UERE (GPS code)

Term

Dilution of Precision (DOP)

Example

PDOP = 2.5 with σ = 3 m gives ~7.5 m accuracy; same σ with PDOP = 5 gives ~15 m accuracy

Definition

Dimensionless factor describing how satellite geometry affects positioning accuracy; lower DOP = better accuracy for same measurement precision.

Term

PDOP (Position DOP)

Example

Excellent: PDOP < 4; Good: PDOP 4–8; Moderate: PDOP 8–16; Poor: PDOP > 16

Definition

3-D position dilution of precision; affects accuracy of X, Y, Z, and clock bias simultaneously.

Term

HDOP (Horizontal DOP)

Example

Typically 0.8–2.5 for open sky; HDOP < 2 is considered good for surveying

Definition

Horizontal dilution of precision; affects accuracy of X and Y only (latitude and longitude).

Term

VDOP (Vertical DOP)

Example

Typically 1.5–3× larger than HDOP due to poor satellite elevation distribution (satellites overhead, not at horizon)

Definition

Vertical dilution of precision; affects accuracy of Z (height/ellipsoid height) only.

Term

UERE (User Equivalent Range Error)

Example

UERE = 5 m typical; UERE = 3 m with dual-frequency and correction models

Definition

Pseudo-range noise equivalent, combining all unmodelled systematic and random errors; typical 3–10 m for standard GPS.

Formula

Correction = ρ_true_reference - ρ_observed_reference

Meaning

ρ_true = known pseudorange to reference station; ρ_observed = measured pseudorange at reference; difference = error to broadcast

Watch Out

Assumes errors are CORRELATED between base and rover (true for iono/tropo/orbit within ~20–30 km); multipath is NOT correlated

When To Use

Compute correction at a base station on known point; apply to rover to remove common errors

Formula

Accuracy_rover ≈ 0.5–1 m (DGPS, static differential)

Meaning

Horizontal accuracy after differential correction; depends on baseline length and correction model

Watch Out

Accuracy DEGRADES with longer baselines (>50 km); iono/tropo decorrelation; use precise ephemeris for longer lines

When To Use

Planning survey accuracy with DGPS (Code-based differential)

Value

5–10 m

Symbol

σ_standalone

Quantity

Standalone GPS accuracy

Value

0.5–1 m

Symbol

σ_DGPS_5km

Quantity

DGPS accuracy (5 km baseline)

Value

1–2 m

Symbol

σ_DGPS_50km

Quantity

DGPS accuracy (50 km baseline)

Value

~100 km (accuracy degrades beyond)

Symbol

L_DGPS_max

Quantity

Max practical DGPS baseline

Value

1–10 Hz

Symbol

f_corr

Quantity

Correction update rate (typical)

Term

Differential GNSS (DGPS)

Example

Reference on monument broadcasts corrections; rover 20 km away applies them → accuracy improves from ~5 m to ~0.5–1 m

Definition

Technique where corrections computed at a known-position reference station are transmitted to rover receiver to remove common systematic errors.

Term

Base Station (Reference Station)

Example

Coast Guard DGPS network uses fixed reference stations to broadcast 50 Hz corrections over radio

Definition

Receiver on a point of known coordinates (from prior survey or high-order control); computes and broadcasts corrections to rovers.

Term

Rover

Example

Survey crew with rover receiver receives DGPS corrections from base on monument; position improves in real-time

Definition

Mobile receiver that applies corrections from base station to improve its own position estimate.

Term

Baseline

Example

5 km baseline: 90% error correlation; 50 km: ~70%; 100 km: ~50%

Definition

Vector distance between base and rover; errors decorrelate at longer baselines (typically >50 km for DGPS)

Formula

RTK Accuracy ≈ 2–5 cm horizontal + 3–10 cm vertical (fixed integers)

Meaning

Centimetre-level accuracy for real-time positioning with carrier-phase differential and resolved ambiguities

Watch Out

Accuracy valid ONLY after ambiguity fixing (status = FIXED); before fix (FLOAT), accuracy is similar to DGPS (0.5–1 m)

When To Use

Machine guidance, stake-out, rapid control densification; only when fix status is FIXED

Formula

Ambiguity Search Space = N_sat × N_freq × (2 × max_cycle_slip + 1)

Meaning

Total integer combinations to test; N_sat = satellites, N_freq = frequencies; cycle slip ≈ 1–3 cycles typical

Watch Out

Fixing is PROBABILISTIC; low PDOP, weak signals, or multipath cause false fix (wrong integer); always validate before use

When To Use

Understand why RTK initialization takes seconds (with dual-frequency) vs minutes (single-frequency)

Formula

Time-to-Fix (s) ≈ N_ambiguities / (f_update × SNR)

Meaning

Rough estimate of convergence time; depends on receiver update rate, signal strength, and geometry

Watch Out

Poor geometry (high PDOP) or obstructed sky significantly increases time-to-fix; can exceed 5 minutes in bad conditions

When To Use

Field planning: how long to wait after initializing RTK?

Value

2–5 cm

Symbol

σ_RTK_H

Quantity

RTK horizontal accuracy (FIXED)

Value

3–10 cm

Symbol

σ_RTK_V

Quantity

RTK vertical accuracy (FIXED)

Value

0.5–1 m

Symbol

σ_RTK_float

Quantity

RTK accuracy (FLOAT, before fix)

Value

10–30 s

Symbol

t_fix_dual

Quantity

Typical time-to-fix (dual-freq)

Value

1–5 minutes

Symbol

t_fix_single

Quantity

Typical time-to-fix (single-freq)

Value

20–50 km (standard); ~100 km with network

Symbol

L_RTK

Quantity

RTK baseline limit

Value

1–2 s

Symbol

Δt_link

Quantity

Correction link latency (max)

Term

Real-Time Kinematic (RTK)

Example

Construction equipment or survey drone uses RTK for autonomous stake-out; position updates 1–20 Hz at cm accuracy

Definition

Real-time carrier-phase differential GNSS with integer ambiguity resolution, providing cm-level positioning without post-processing.

Term

Fixed Solution (Fix)

Example

After initialization, receiver enters FIXED mode; accuracy typically 2–5 cm if geometry and signal strength remain good

Definition

Integer ambiguities are resolved to integers with high confidence; solution has cm-level accuracy.

Term

Float Solution (Float)

Example

During RTK initialization, receiver shows FLOAT status with ~0.5 m accuracy; once fixed, jumps to 2–5 cm

Definition

Ambiguities solved as real numbers (not integers) via least-squares; accuracy similar to DGPS (0.5–1 m); lower than FIXED.

Term

Ambiguity Initialization / Time-to-Fix

Example

Dual-frequency: 10–30 s typical; single-frequency: 1–5 minutes or longer

Definition

Time required to resolve integer ambiguities from FLOAT to FIXED status; depends on geometry, satellite count, and baseline.

Term

RTK Network (RTN)

Example

Philippines: PRISM (PRS-based RTN) provides coverage; single rover connects to nearest base instead of owning base station

Definition

Regional network of fixed base stations (e.g., CORS) that compute and transmit real-time corrections via wireless link.

Term

NTRIP (Network Transport of RTCM via Internet Protocol)

Example

Receiver connects via cellular/WiFi to NTRIP server; receives RTK corrections and achieves cm accuracy

Definition

Standard protocol for distributing GNSS correction data (RTCM) over internet to mobile receivers; enables internet-based RTK.

Formula

Accuracy ≈ 5 mm + 1 ppm × baseline

Meaning

Typical accuracy after post-processing static survey with dual-frequency carrier phase; 5 mm fixed error + 1 ppm of baseline length

Watch Out

Assumes good geometry, minimal multipath, and convergence; poor conditions can degrade to 1–2 cm

When To Use

Estimate precision of baseline after post-processing (e.g., survey network, control densification)

Formula

Session Duration ≥ (10 + baseline_km) minutes

Meaning

Rough rule-of-thumb for static observation duration to achieve ambiguity resolution and stable solution

Watch Out

Modern dual-freq receivers with good sky view can fix faster (5–10 min for 20 km); poor geometry requires longer

When To Use

Plan field sessions: 5 km line needs ~15 min; 50 km needs ~60 min

Value

5 mm + 1 ppm baseline

Symbol

σ_static

Quantity

Static survey accuracy (dual-freq)

Value

1–2 cm + 1 ppm

Symbol

σ_rapidstatic

Quantity

Rapid-static accuracy

Value

30 min (10 km baseline); 2–4 h (100 km)

Symbol

t_session

Quantity

Typical static session duration

Value

5–10 min (dual-freq, good sky)

Symbol

t_min_fix

Quantity

Minimum session for ambiguity fix

Term

Static Survey

Example

Survey crew occupies point A for 30 minutes (carrier phase), then point B for 30 minutes; baseline A–B computed with 5–10 mm accuracy

Definition

Both receiver and surveyor remain stationary during session; processed in post-processing mode; highest accuracy (~5 mm + 1 ppm).

Term

Rapid-Static

Example

Quick control densification: occupy each point 10 min with modern receiver → 1–2 cm accuracy, much faster than traditional static

Definition

Shortened static session (5–10 min) with dual-frequency receiver and resolved ambiguities; accuracy ~1–2 cm.

Term

Kinematic Survey

Example

Drone surveys: fly trajectory while tracking; post-process to get cm-level orthophoto/DTM

Definition

Rover moves along trajectory while tracking satellites; processed in post-processing; intermediate accuracy (few cm) if well-initialized.

Term

Post-Processing

Example

Collect 2-hour static session on 100 km baseline; download precise ephemeris; post-process offline; achieve 5–10 mm accuracy

Definition

GNSS data processing done after field session complete; uses stored raw observations and precise ephemeris; no real-time correction link needed.

Formula

WGS84 (World Geodetic System 1984)

Meaning

Geocentric reference frame fixed to Earth's center of mass; origin at Earth's centre; Z-axis toward North Pole; X-axis toward 0° meridian/equator

Watch Out

WGS84 ≠ PRS92; difference up to ~1 m in Philippines; must apply transformation to comply with RA 8560

When To Use

All GPS/GNSS measurements are computed in WGS84; must transform to local datum (PRS92) for Philippine surveys

Formula

PRS92 (Philippine Reference System 1992) based on Clarke 1866 ellipsoid

Meaning

Local datum for Philippines; uses Clarke 1866 ellipsoid (a = 6378206.4 m, e² ≈ 0.00674); fixed to monument constellation

Watch Out

Never use WGS84 directly for Philippine property or engineering surveys; VIOLATION of RA 8560 and RA 4374

When To Use

All Philippine land surveys, property deeds, engineering projects must use PRS92 coordinates and monuments

Formula

WGS84 to PRS92 transformation: Δ E ≈ −127.5 m, Δ N ≈ −116 m (rough, Luzon region)

Meaning

Approximate shift between WGS84 and PRS92 in Philippines; varies by region (Visayas, Mindanao differ)

Watch Out

Official PRS92–WGS84 transformation uses 7-parameter Helmert or region-specific grids (BX files); do NOT use simple shift

When To Use

Quick sanity check: if WGS84 and PRS92 differ by >2 m, check transformation parameters

Value

6378137 m

Symbol

a_WGS84

Quantity

WGS84 semi-major axis

Value

1/298.257

Symbol

f_WGS84

Quantity

WGS84 flattening

Value

6378206.4 m

Symbol

a_Clarke

Quantity

Clarke 1866 (PRS92) semi-major axis

Value

ΔE ≈ −127.5 m, ΔN ≈ −116 m

Symbol

δ_LuzonShift

Quantity

WGS84–PRS92 shift (Luzon, approx)

Value

1992 (frozen; no plate motion updates)

Symbol

t_PRS92

Quantity

PRS92 epoch

Value

5–10 cm/year

Symbol

v_plate

Quantity

Typical plate motion (Philippines)

Term

WGS84 (World Geodetic System 1984)

Example

GPS satellite ephemeris in WGS84; raw receiver coordinates in WGS84; must transform to PRS92 for Philippine use

Definition

Geocentric reference frame (origin at Earth's centre); global standard for GNSS. Uses WGS84 ellipsoid (a = 6378137 m; f = 1/298.257).

Term

PRS92 (Philippine Reference System 1992)

Example

Property deed coordinates in PRS92; survey monuments in PRS92; engineering design in PRS92

Definition

Local datum for Philippines; fixed to monuments (NAMRIA control points); uses Clarke 1866 ellipsoid; required by law (RA 8560, RA 4374).

Term

ITRF (International Terrestrial Reference Frame)

Example

IGS precise ephemeris and station coordinates in ITRF; permanent monitoring stations track plate tectonics

Definition

Global, high-precision geocentric frame; multiple realizations (ITRF2000, 2005, 2008, 2014, 2020); supercedes WGS84 for geodetic work.

Term

Datum Transformation / Shift

Example

WGS84 → PRS92: apply 7-param transform or NAMRIA grid; PRS92 → WGS84: inverse transform

Definition

Mathematical conversion between two reference frames; 7-parameter (Helmert) transform or region-specific grid shift (BX file).

Term

Plate Tectonics & Frame Realization

Example

PRS92 coordinates valid for 1992 epoch; Philippine monument at 0° has drifted ~1 m by 2024; modern surveys use dynamic WGS84 or PRS92/2015 variant

Definition

Earth's crust moves ~5–10 cm/year; ITRF realizations updated every ~3–5 years; PRS92 fixed to historical epoch (1992) → accumulates ~1 m drift.

Value

24–30 (typically 31–33 active)

Symbol

n_GPS

Quantity

GPS satellites

Value

24 (3 orbital planes × 8 satellites)

Symbol

n_GLONASS

Quantity

GLONASS satellites

Value

30 (24 active + 6 backup)

Symbol

n_Galileo

Quantity

Galileo satellites

Value

30+ (MEO + GEO + IGSO)

Symbol

n_BeiDou

Quantity

BeiDou satellites

Value

20,200 km

Symbol

h_GPS

Quantity

GPS orbital altitude

Value

19,100 km

Symbol

h_GLONASS

Quantity

GLONASS orbital altitude

Value

23,200 km

Symbol

h_Galileo

Quantity

Galileo orbital altitude

Term

GPS (Global Positioning System / NAVSTAR)

Example

GPS alone provides 4–12 satellite visibility at any time; minimum 4 for 3-D fix

Definition

U.S. space-based GNSS constellation; 24–30 satellites in 6 orbital planes at ~20,200 km altitude; all-in-view within 5 min typical.

Term

GLONASS (Globalnaya Navigazionnaya Sputnikovaya Sistema)

Example

Combined GPS + GLONASS improves satellite availability in obstructed areas (urban canyons, forests)

Definition

Russian GNSS constellation; 24 satellites in 3 orbital planes at ~19,100 km; same dual-frequency architecture as GPS.

Term

Galileo (Galileo System)

Example

Full operational constellation as of 2024; improving accuracy and redundancy

Definition

European GNSS constellation; 30 satellites (24 active + 6 backup) at ~23,200 km; newer frequencies (E1, E5a, E5b, E6) with civilian access.

Term

BeiDou (BDS / Compass)

Example

Strongest coverage in Asia-Pacific region (Philippines included); improving rapid growth

Definition

Chinese GNSS constellation; 30+ satellites (MEO + GEO + IGSO orbits) at various altitudes; dual-frequency for civilians.

Term

Multi-GNSS / Multi-Constellation Receiver

Example

Modern survey receivers track all 4 constellations; fixes ambiguities 2–3× faster than GPS-only

Definition

Receiver tracking GPS + GLONASS + Galileo + BeiDou simultaneously; improves satellite count, geometry, and convergence speed.

Value

1998

Symbol

yr_RA8560

Quantity

RA 8560 enactment year

Value

1965 (RA 4374)

Symbol

yr_PRS92

Quantity

PRS92 adoption year

Value

4 zones (Luzon, Visayas, Mindanao, Palawan with PCS)

Symbol

n_zones

Quantity

PPCS standard zones

Term

RA 8560 (Geodetic Engineer License Law, 1998)

Example

Only licensed Geodetic Engineers (PRC certified) can conduct surveys for property deeds, cadastral records in Philippines

Definition

Philippine law defining professional qualification and scope of geodetic engineers; mandates PRS92 for all surveys; governs cadastral/property surveys.

Term

RA 4374 (PRS92 Adoption & Standardization, 1965)

Example

All Philippine government maps, coordinates, property records must use PRS92; non-compliance invalidates legal documents

Definition

Philippine law adopting Clarke 1866 ellipsoid and PRS92 datum as official reference system; established NAMRIA as official mapping agency.

Term

PD 1529 (Surveyors License Decree, 1978; repealed by RA 8560 but principles remain)

Example

Historical context for evolution of surveying profession in Philippines; RA 8560 supersedes

Definition

Historical decree on surveyor licensing; modern surveying (GNSS-based) regulated under RA 8560 instead.

Term

CA 141 (Commonwealth Act 141 / Public Land Act, 1936)

Example

Surveys under CA 141 must follow RA 8560 standards; GNSS surveys tied to PRS92 monuments

Definition

Philippine land ownership and cadastral survey law; defines free patents, homesteads, and survey requirements for public lands.

Term

NAMRIA (National Mapping and Resource Information Authority)

Example

NAMRIA publishes transformation parameters (PRS92 ↔ WGS84); maintains PRISM (PRS92-based RTN) for real-time GNSS

Definition

Philippine government agency maintaining official geodetic control network (PRS92 monuments), maps, and reference systems.

Term

PPCS (Philippine Plane Coordinate System)

Example

Survey blueprints, engineering designs, cadastral maps use PPCS coordinates (Easting, Northing in metres)

Definition

Projected (plane) coordinate system based on PRS92 and UTM projection (Transverse Mercator); coordinates in metres.

Values

• ~1 m (coarse)
• ~2–5 mm (precise)

Property

Precision

Values

• UNAMBIGUOUS (direct range)
• AMBIGUOUS (integer N unknown)

Property

Ambiguity

Values

• Fast (~1 s)
• Slow (minutes+ for fixing N)

Property

Speed of measurement

Values

• High (1–3 m error)
• Low (5–50 mm error)

Property

Multipath sensitivity

Values

• Navigation, DGPS, rapid positioning
• Precise geodetic surveys, RTK, control

Property

Typical use

Values

• NO (inherently unambiguous)
• YES (critical; time-consuming)

Property

Integer ambiguity resolution needed?

Values

• None
• YES; must detect & repair

Property

Cycle slip problem

Values

• Real-time or post
• 0.5–1 m
• 1–2 min
• Navigation, rapid surveys, <50 km baseline

Property

DGPS (Pseudorange Diff)

Values

• Real-time (FIXED)
• 2–5 cm (FIXED); 0.5–1 m (FLOAT)
• 10 s–5 min
• Stake-out, machine guidance, 20–50 km baseline

Property

RTK (Carrier Phase Diff)

Values

• Real-time (unfixed)
• 0.5–1 m
• Immediate
• Same as DGPS; no benefit until fixed

Property

RTK (FLOAT, not fixed)

Values

• Post-processing (offline)
• 5 mm + 1 ppm baseline
• Hours–days
• Precise control surveys, long baselines 50+ km

Property

Static Post-Processing

Values

• Post-processing
• 1–2 cm + 1 ppm
• 10 min + post-proc
• Quick control densification, 5–20 km

Property

Rapid-Static

Values

• USA
• 24–30
• 20,200
• 6
• L1 (1575.42 MHz), L2 (1227.60 MHz)
• Global

Property

GPS

Values

• Russia
• 24
• 19,100
• 3
• L1 (1602+N×562.5 kHz), L2
• Global

Property

GLONASS

Values

• Europe
• 30
• 23,200
• 3
• E1, E5a, E5b, E6
• Global (full 2024)

Property

Galileo

Values

• China
• 30+
• Various (MEO/GEO/IGSO)
• Mixed
• B1, B2, B3
• Strong Asia-Pacific

Property

BeiDou

Values

• Excellent
• ~5–10 m
• ~7–15 m
• Ideal (rare without augmentation)

Property

< 2

Values

• Good
• ~10–20 m
• ~15–30 m
• Recommended for surveys; good geometry

Property

2–4

Values

• Moderate
• ~20–40 m
• ~30–60 m
• Acceptable; caution on critical work

Property

4–8

Values

• Poor
• ~40–80 m
• ~60–120 m
• Avoid if possible; degraded solution

Property

8–16

Values

• Very Poor
• > 80 m
• > 120 m
• REJECT; do not use for surveys

Property

> 16

Values

• Earth's centre
• WGS84 (a=6378137 m)
• Geocentric, global
• Global (GPS)
• NOT acceptable for final legal/property surveys

Property

WGS84

Values

• Earth's centre (fixed 1992)
• Clarke 1866 (a=6378206.4 m)
• Local Philippine datum, frozen epoch
• Philippines
• MANDATORY for all Philippine surveys by law (RA 8560)

Property

PRS92

Values

• Earth's centre (continuously updated)
• GRS80 (nearly WGS84)
• Geocentric, high-precision global
• Global (geodetic community)
• Optional; more accurate than WGS84 but requires transformation to PRS92

Property

ITRF