Satellite Geodesy and GNSS - Concept Map
Global Navigation Satellite Systems (GNSS) as the Primary Tool of Modern Geodesy
Related concepts
GNSS Positioning Principle
Sub concepts
- Trilateration
- Satellite Geometry
- Receiver Position (X, Y, Z)
- Receiver Clock Bias (Δt)
- Minimum 4 Satellites Required
Relationship to central
Foundational method underlying all GNSS operations
GNSS Observables
Sub concepts
- Pseudorange (ρ = c·Δt)
- Carrier Phase
- Integer Ambiguity Resolution
- Measurement Accuracy Levels
- Metre-Level vs Millimetre-Level Precision
Relationship to central
Raw measurements that enable positioning
Error Sources and DOP
Sub concepts
- Satellite Clock Errors
- Orbital Errors
- Ionospheric Delay
- Tropospheric Delay
- Multipath
- Receiver Noise
- Dilution of Precision (DOP)
- PDOP, HDOP, VDOP, GDOP
Relationship to central
Factors that limit positioning accuracy
Differential and RTK Methods
Sub concepts
- DGPS (Differential GPS)
- Static Differential
- Base Station Corrections
- RTK (Real-Time Kinematic)
- Carrier-Phase Differential
- cm-Level Accuracy
- Real-Time Processing
Relationship to central
Techniques for improving positioning accuracy
Reference Frames and Datums
Sub concepts
- WGS84 Datum
- ITRF (International Terrestrial Reference Frame)
- PRS92 (Philippine Reference System)
- Frame Transformation
- Geocentric vs Local Datums
- Datum Conversion Requirements
Relationship to central
Coordinate systems where GNSS positions are expressed
GNSS Constellations
Sub concepts
- GPS (United States)
- GLONASS (Russia)
- Galileo (European Union)
- BeiDou (China)
- Regional Systems
- Constellation Geometry
Relationship to central
Satellite systems providing global navigation signals
Practical Applications in Philippine Geodesy
Sub concepts
- Control Densification
- Stake-Out Operations
- Land Survey Documentation
- Compliance with RA 4374 and RA 8560
- PRS92 Tie-In Requirements
- PPCS/UTM Zone Integration
Relationship to central
Real-world implementation aligned with PRC standards
Concept connections
- GNSS Positioning PrincipleTrilaterationGeometric foundation: solving 4 equations from 4 satellites to find X, Y, Z, Δt
- GNSS Positioning PrinciplePseudorangeObservable used to measure distance from each satellite
- PseudorangeCarrier PhaseAlternative observable with higher precision but requiring ambiguity resolution
- Error Sources and DOPAccuracyDOP multiplies measurement error to determine final positioning accuracy
- Satellite GeometryDilution of PrecisionWell-spread satellites produce low DOP; clustered satellites produce high DOP
- Ionospheric DelayDGPS CorrectionsDifferential methods remove common atmospheric delays at similar locations
- Tropospheric DelayRTK Real-Time KinematicCarrier-phase RTK less sensitive to tropospheric effects than pseudorange
- Carrier PhaseRTK Real-Time KinematicRTK relies on real-time carrier-phase differential measurements
- RTK Real-Time KinematicCentimetre-Level AccuracyRTK achieves cm-level positioning through rapid ambiguity resolution
- WGS84 DatumPRS92 DatumGNSS operates in WGS84; results must be transformed to PRS92 for Philippine surveys
- PRS92 DatumPPCS/UTM ProjectionPRS92 geodetic coordinates are projected to PPCS/UTM for practical survey work
- PPCS/UTM ProjectionSurvey DocumentationFinal survey coordinates reported in PPCS/UTM Grid system per RA 8560
- Static DGPSControl DensificationStatic differential GPS used to establish new control points tied to known bases
- RTK Real-Time KinematicStake-OutRTK enables real-time positioning for setting-out survey points on ground
- GNSS ConstellationsSatellite GeometryMore constellations (GPS + GLONASS + Galileo) improve overall geometry and availability
- Multipath ErrorRTK AccuracyMultipath is a major error source limiting cm-level RTK accuracy in urban areas
- Integer Ambiguity ResolutionCarrier PhaseCore challenge in carrier-phase processing: determining integer wavelength count
- PRC Licensure StandardsPRS92 Mandatory UseRA 8560 requires all Philippine surveys in PRS92; WGS84 is not acceptable
- RA 4374 StandardsMonument EstablishmentLegal requirement for proper marking and documentation of geodetic control points
- Real-Time KinematicNTRIP/Radio CommunicationRTK requires real-time base station corrections via communication link
- Receiver Clock BiasFourth SatelliteClock bias is the fourth unknown requiring a fourth pseudorange equation
- Pseudorange EquationReceiver Clock BiasEach pseudorange includes the receiver clock error Δt as unknown
- DOP AnalysisPre-Survey PlanningEngineers check DOP forecasts to plan optimal survey window for best geometry
- Accuracy = DOP × σError PropagationFundamental equation relating geometry (DOP) to measurement precision (σ) and final accuracy
- Base Station CorrectionsCommon Error RemovalDGPS base computes residual errors that are subtracted from rover measurements
- 7-Parameter Similarity TransformWGS84 to PRS92 ConversionPrecise mathematical transformation accounting for translation, rotation, and scale
- Geoid ModelEllipsoidal to Orthometric HeightGeoid undulation N converts ellipsoidal height h to orthometric H per H = h - N
- Survey Quality AssuranceRA 8560 ComplianceAll surveys must meet RA 8560 accuracy and documentation standards before acceptance
Diagrams
Satellite Geodesy and GNSS - Comprehensive Concept Hierarchy
Hierarchical mind map showing the complete structure of Satellite Geodesy and GNSS, organized from the central concept outward through positioning principles, observables, errors, differential methods, reference frames, and practical Philippine applications. This map connects all major topics and shows how each concept branches into more specific subtopics.
GNSS Positioning Process Flow - From Signal to Final Coordinates
Complete workflow from satellite signal acquisition through final geodetic control point establishment. Shows the decision points (satellite lock, method selection, quality checks), the role of differential corrections, and the critical transformation to PRS92 datum and PPCS/UTM projection required for Philippine survey work. Includes compliance with RA 8560 and RA 4374.
Error Sources and Their Impact on Positioning Accuracy
Systematic breakdown of error sources affecting GNSS positioning: satellite-based errors (clock and orbit), atmospheric delays (ionospheric and tropospheric), and reception errors (multipath and noise). Shows how these combine through the DOP geometry factor to produce the final positioning accuracy, and how differential and RTK methods mitigate these errors to achieve cm-level precision for geodetic applications.
Decision Tree: Selecting GNSS Method for Philippine Geodetic Work
Practical decision tree for Philippine geodetic engineers selecting the appropriate GNSS method based on accuracy requirements. Routes from preliminary surveys (standard GPS) through control densification (static DGPS/post-processing and RTK) to research-grade work (carrier-phase static). Emphasizes mandatory PRS92 transformation, PPCS/UTM conversion, compliance with RA 8560 quality standards, and RA 4374 monument establishment procedures required by PRC for licensed geodetic engineers.
From WGS84 to PRS92: Coordinate Transformation Workflow
Complete workflow for transforming GNSS results from the global WGS84 geocentric frame to the Philippine Reference System (PRS92) and Plate-Motion cassini Projection System (PPCS/UTM). Shows the critical steps: geoid model application for height conversion, 7-parameter similarity transformation with validation, projection to PPCS zones, and final documentation per RA 8560. Emphasizes that Philippine law requires all survey results in the local datum, not WGS84.
Typical Error Budget for Real-Time GNSS Positioning
Breakdown of typical error contributions in RTK positioning achieving 1–3 cm accuracy. Shows that even with differential corrections, residual errors in orbit, clock, ionosphere, and multipath remain; ambiguity uncertainty is significant. Demonstrates why cm-level RTK accuracy requires not just geometry and measurements, but careful error modeling and proper reference-frame transformation to PRS92.
Pseudorange vs Carrier-Phase Comparison and Selection
Detailed comparison of pseudorange (ρ = c·Δt) and carrier-phase observables. Pseudorange provides metre-level accuracy with fast convergence and no ambiguity issues—ideal for basic GPS. Carrier-phase offers millimetre-level precision but requires integer ambiguity resolution and continuous lock—essential for geodetic-quality RTK and precise surveys. Modern practice combines both observables in differential and RTK methods to achieve optimal accuracy and reliability.