7.2 Data
There are three main types of data that we need to collect in any GNSS survey:
- Metadata – Data about our survey
- Position – GNSS Positional information about points or locations
- Attributes – location intelligence
Metadata
Our understanding where data is coming from, why it has been created, who collected it, what errors might be impacting it and how accurate it is are all critical in ensuring it is used appropriately. The creation of all this information about data is an important part of any GNSS survey. This “data about data” is referred to as metadata, and should be recorded for every GNSS survey.
Metadata allows any person to look at any dataset and understand how it was created, by whom and a whole bunch of other information. There are a number of international standards about what metadata needs to be created for spatial datasets.
In GNSS surveying, standards like SP1 and a concept called legal traceability provide a combined framework for what metadata might need to be collected for a GNSS survey. Legal traceability is the concept that there is a way to link a physical measurement to a standard.
More generally, metadata can most easily be understood as being the WHERE, WHEN, WHY, HOW, WHO and WHAT of a dataset:
- Where was the data collected?
- the physical location
- which datum or projection the data was collected in
- When was the data collected?
- Why was the data collected?
- Was it for a high accuracy survey, or just to locate the footpaths in a park?
- The WHY will give an indication of the accuracy and quality of a dataset
- How was the data collected?
- What kind of technique was used?
- What kind of equipment was used?
- What were the serial numbers, brand and model of the equipment?
- Was redundancy of measurements considered, and how was it undertaken?
- Who collected the data?
- What were the names of the people involved in the collection?
- What were their qualifications or experience in undertaking this kind of data collection?
- Who did they work for?
- Who was the client?
- Who owns the data?
- What was the data?
- What format was it collected in?
- What file types were used and what translations or transformation between file types occurred?
- Are there supporting files, like scans of field notes or photos?
- How large are the files?
- Where is the data stored?
An example of basic metadata that could be collected for a GNSS project is shown in Table 7.1(a).
Table 7.1(a): Survey metadata
| Survey site: | USQ Springfield | Name of surveyor/s: | Jane Smith |
| Date: | 01/05/2054 | Project name: | SVY1110 Tut 1 |
| GNSS antenna type: | SVMax | GNSS antenna serial number | 123456 |
| GNSS Receiver type: | SVRX | GNSS receiver serial number | 789456123 |
| Datum: | GDA2054 | Weather conditions: | Fine, 30, Slight wind |
| PM used for datum: | PM123456 | Raw data file name: | 20540501_1110.ab |
Position information
As previously discussed, the most important component of positional information is understanding the