10.1.3 GPS and Quality Issues

MANAGING QUALITY : TRACKING THE GPS SURVEYING PROCESS

Although the analogy cannot be carried too far, it is nevertheless useful to consider a GPS surveying "job" as in the case of any other product or service, and to therefore study the project life cycle :

Customer request

Feasibility study

Analysis

Design

Production

Delivery

For each of the above, the inputs and outputs (or outcomes) may be identified. Take for example a GPS survey project.

Customer Request can be considered to be the process of defining the Project Objectives :

• Document the instructions.
• Determine if the required outputs can be: (a) produced, (b) verified, and (c) controlled.

The Feasibility study phase is concerned with the Project Definition (section 5.2.1):

• Identify the inputs, including: (a) reason for survey, (b) accuracy requirements, (c) completion date, (d) item to be delivered, (e) budget allocation, and (f) project authorisation/definition documentation.

   

• Assign responsibilities, such as: (a) project director, (b) technical manager, (c) design personnel, and (d) survey personnel.

   

• Generate definitive technical data for, for example: (a) procurement, (b) execution of the job, and (c) verification that products and processes conform to specifications.

   

• Prepare the (output) specifications, including: (a) stations and network geometry, (b) equipment and observation technique, (c) computation and adjustment, (d) project management, and (e) acceptance and rejection criteria.

The Analysis and Design phases is synonymous with Mission Planning and Reconnaissance (section 5.2.2 and section 5.3.1):

• Assemble the inputs, including: (a) project definition documentation, (b) planning and design materials, (c) information regarding existing survey marks, and (d) liaison with public utilities, etc.

   

• Define the station selection criteria, for example: (a) suitability, (b) site access, (c) sky visibility, (d) multipath sources, (e) need for eccentric stations, and (f) azimuth mark.

   

• Perform the reconnaissance to: (a) review proposed use of existing stations, (b) check suitability of new stations, and (c) finalise station selection.

   

• Carry out the network design task, taking into account such factors as: (a) accuracy specifications, (b) connections to existing stations, (c) observation techniques, (d) number of station revisits, (e) independent baselines, (f) access and travel times, and (g) data processing considerations.

   

• Generate the necessary documentation, including: (a) map showing all stations and independent baselines, (b) sky plots, (c) observing schedule, and (d) reconnaissance forms, recovery and access sketches, photographs, etc.

   

• Prepare mission planning outputs, for example: (a) schedule of baselines to be observed each day, for each field party, (b) observing technique for each baseline (dependent on such things as baseline length, number of visible satellites, PDOP range, whether modern or conventional static GPS technique is to be used), (c) proposed start and end times, (d) numbering and naming conventions for stations and data files, and (e) personnel to be used.

The Production phase is concerned with the Data Acquisition and Primary Data Processing (section 5.4.3, section 5.5.1, Chapter 7 and Chapter 8):

• Carry out the necessary onsite activities, including: (a) site checks and field documentation (verify site, etc.), (b) instrument setup and initialisation (antenna centring and height measurement, cable connections and power supply, enter appropriate receiver parameters, etc.), (c) instrument operation and data collection monitoring, and (d) data download, demount of hardware and travel to next site.

   

• Process baselines: (a) setup data processing software parameters, (b) data pre-processing, initial solutions and archiving, (c) process double-differenced data (dual-frequency? conventional static or modern technique? independent baselines and approximate coordinates?), and (d) apply QC procedures.

The Delivery stage is concerned with the Network Adjustment and Result Transformation (Chapter 9 and Chapter 11):

• Secondary network adjustment activities, including: (a) minimally constrained solutions, (b) check output, note inconsistencies and determine whether there is a need for reobservation, and then (c) refine adjustment.

   

• Project completion activities, for example: (a) generate full documentation, (b) highlight statistical information on accuracy and reliability, (c) constrain solution to existing control, (d) determine class and order of survey, (e) datum transformation, (f) orthometric height determination, and (g) assessment of total process and communicate with client.

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© Chris Rizos, SNAP-UNSW, 1999