GNSS Positioning Modes for Land Surveys

GNSS Positioning Modes

• GNSS positioning methods include static, rapid static, stop-and-go, kinematic, RTK, and real-time DGNSS
• These methods differ in the way they are employed and the accuracy they provide

GNSS Positioning Modes for Land Surveys

• Guidelines and specifications for land surveys are governed by DAO 2007-29
• Control Survey Accuracy Specifications are based on DMC 2010-13
• LMC No. 2015-01 establishes guidelines for RTK GNSS in lot surveys demanding tertiary accuracy

Two Ways of GNSS Positioning

• Point Positioning:
  • This method uses a single receiver to calculate the user's position.
  • It provides relatively low accuracy
  • Common in handheld GNSS receivers and mobile phones
• Relative Positioning:
  • This method employs two or more receivers simultaneously tracking the same satellites.
  • It provides higher accuracy
  • Used for applications such as surveying, mapping, and precise navigation
  • Techniques include DGNSS and RTK.

Static GNSS Surveying

• The observation time varies from 20 minutes to several hours, depending on the baseline length and the number of visible satellites.
• Measurements are typically taken every 10, 15, or 20 seconds.
• Instrument height must be recorded
• Post-processing of GNSS raw data is necessary for applying differential corrections and precise positioning calculations
• Raw GNSS files often need conversion to the RINEX format for further processing.

Fast (Rapid) Static GNSS Surveying

• The base receiver remains stationary throughout the observation session.
• The rover receiver remains stationary for a short interval, then moves to another point for recording.

Stop-and-Go GNSS Surveying

• Two or more receivers are used.
• A base receiver remains stationary.
• Rover receivers move between unknown points, pausing at each to collect data.

Kinematic GNSS Surveying

• Receivers continuously track satellites without stopping at each point.
• The base receiver remains stationary over the known point.
• The rover receiver moves over the unknown points without stopping.
• Requires post processing to calculate coordinates of unknown points.

RTK GNSS Surveying

• Similar to kinematic surveying, but it uses a higher data rate (at least 1Hz).
• Base receiver measurements and coordinates are transmitted to the rover receiver via a radio link for real-time position calculations.
• Best for large numbers of unknown points in close vicinity to a known point.
• Allows for precise, real time positioning in the order of centimeters.

PPK Surveying

• Used for mapping and surveying requiring centimeter accuracy.
• Data is collected using two receivers; one is a fixed base station; and one or more rovers.
• Post-processing of the data is required.
• Two types: Topo Point Surveys and Continuous Survey.

Real-Time DGNSS

• A code based relative positioning method employing two or more receivers to track the same satellites in real time.
• Ideal when a near submeter positioning is required within few hundred kilometers.

Control Point Establishment Using GNSS Method in the Philippines

• Specifications and procedures for CP establishment are governed by DAO 2007-29 and DMC 2010-13
• These rules address accuracy specifications for various control survey orders.

Control Survey Accuracy Specifications

• Geodetic control surveys have different orders of accuracy (first, second, third, and fourth) varying with relative error, linear error, and vertical accuracy dependent on the survey area.

LMC No. 2015-01

• Provides guidelines on using RTK GNSS for all lot surveys with tertiary accuracy.

Section 1: Registration of Receivers

• RTK GNSS receivers must be registered before use.

Section 2: Procedures and Conditions for the Use of RTK GNSS

• Only Dual Frequency receivers are permissible.
• Use one GNSS receiver as a base station along with at least one rover receiver.
• Ensure the base station has an unobstructed 15-degree horizon clearance.
• The Rover receivers are mounted on range poles supported by bipods.
• All survey areas must have a horizon clearance of at least 15 degrees at all corners.
• ETS is used to supplement the RTK in situations where the 15-degree horizon clearance isn't met.

Other Important Guidelines

• Root Mean Square during RTK GNSS observation should be 35 or lower.
• RTK observation time for each lot corner shouldn't be less than 2 minutes.
• Ensure at least 5 satellites are tracked with good geometry (good DOP value).
• RTK Rover receiver must be initialized before data collection.
• Minimum baseline length of 200 meters but maximum of 1 Km is recommended.
• Distance between RTK observation should be compared to ETS distance.

Annex XX

• Provides a template for GNSS field sheets (GPS Station Field Sheet)

Section 24:

• Contains guidelines to determine GNSS observation time (duration) for Static and Rapid Static surveys relative to different types of receivers and baseline lengths.

DMC 2010-13 Provisions

• Covers various aspects, from control point establishment to data processing procedures to ensure the accuracy and reliability of GNSS surveys in the Philippines.
• Provides detailed instructions on aspects such as survey area geometry, station visibility, instrument setup, observation period, and more for precise measurements.