Introduction
This practical work intends to develop skills for undertaking a GPS survey and processing the outcomes of the survey with the aid of commercial software. The eventual outcome of the endeavor is to encourage team work skills of thinking critically when looking for problems that might arise in the data as well evaluating the quality of the final results.
Objectives
- Make use of GPS technology in identifying the coordinates of a number of benchmarks which are relative to an established station of reference with the aid of an observation method referred to as the rapid static baseline.
This exercise is concerned with:
- acquiring information regarding procedures of GPS baseline survey
- Learning a skill – “drive” a GPS receiver and the software
- exercise skills of communication such as writing reports
- Education of the self which is important with regard to the principles and practice of surveying GPS.
Methodology
Field Procedure
- Install a 1200 GPS receiver for collecting data on static: Data sampling rate 1Hz (epoch interval: 1 second); Elevation Mask angle: 15 degree; GPS only (do not select GLONASS option).
- At a given position (B335), gather data for observation for a period of 20 minutes with the aid of the receiver and give it the name Stn A. On the roof of the Electrical Engineering (EE) building an operation of a reference receiver will be conducted.
- The above task should be done in a different place such as a physics lawn. Coordination of satellite tracking will be absent since the operation of EE reference receiver will be non-stop.
Observation Session
Recording of the observations has taken place at varied times during the day as indicated in Table 1
Office Procedure
Data preparation
- Data should be downloaded promptly without delay into the computer in EE402.
- Observation data for the reference station should also be downloaded.
Processing
Processing of the data is expected to be conducted using Leica Geo office software which is availed. Two methods which assist in identifying the coordinates of the station are available which were employed in carrying out the practical: Single point positioning method, and baseline method which are able to use both pseudo‐range and carrier‐phase measurements in identifying components of the baseline.
Single Point Positioning (SPP)
Single point positioning (SPP) is the process of determining coordinates of a receiver with regard to the reference frame of the earth (WGS84) by signal intersection from four or more GPS satellites. SPP utilizes code solution type gathering at one station in the course of the specified time period. GPS principle has its basis on some simple physics and geometry concepts. By making use of varying ranges between surface point and satellites distributed in space, a GPS system has the capacity of identifying the location of a ground point. Therefore, making an assumption that the coordinates of a satellite are familiar, the point of intersection of three different satellites can determine the ground point. In geometry, GPS encompasses an identification of the 3-D coordinates and the rectification of the time error- four strange parameters. This implies that determining the position requires measuring four satellites. The problems below must be solved in order to implement the right positioning.
- Locating the satellite coordinates always
- Measuring the range between the satellite and ground point accurately.
Pseudo‐range Baseline Solution
To measure pseudo-range, signals sent by satellites in the skies are timed. All the satellites transmit information including the time the messages were sent, accurate information about the orbit and the general health of the system and the rough orbits of entire GPS satellites.