Data Acquisition, Remote Sensing and Metadata

• One of the most expensive GIS activities
• Many diverse sources (source integration, data fusion)
• Different methods needed for different variables
• Two broad types of collection
  • Data capture (direct collection)
  • Data transfer
• Two broad types of data
  • ​Primary
  • Secondary

Data Capture/Transfer Methods: Digitiser - Manually digitising existing paper maps Surveying - record data directly in the field

• Theodolite, GPS (Global Positioning System)

3D Scanner - scan the objects and generate vast point clouds

Several possible methods:

• Remote sensing image
• Aerial photo
• Scanning existing sources

Resolution is key consideration

• Spatial: pixel size and range
• Spectral: range/frequency of electromagnetic radiation
• Temporal

Digitizer uses a digitizing tablet to trace the points, lines and polygons of a hard copy map Digitizing is very time consuming and labour-intensive. It was a main approach for vector data capture

• This is a device that analyses a real world object or environment to collect data on its shape and possibly its appearance

• It measures distance by illuminating a target with a laser and analysing the reflected light.

LiDAR: Light Detection And Ranging Vast point clouds which require careful processing.

GPS: a satellite navigation system that provides location information anywhere on the Earth. How GPS works:

• The GPS satellites circle the Earth in an extremely precise and predefined orbit;
• Each satellite continuously transmits a time signal to the Earth (microwave);
• GPS receivers get these time signals from 3+ satellites and use triangulation mathematics to calculate the exact location.

GPS data capture: easier, cheaper, quicker but slightly less accurate, differential GPS used to improve accuracy.