Drone Surveying

This is with reference to a Real World Project (Example Project)

Step 1 – Identify the surveying requirements

• Identify accuracy required
• Confirm if Global or Relative accuracy is required
• Evaluate if Drone Technology is suitable
• If Drone Technology is not suitable – use traditional methods, total station and GPS Rover.

Project Example – Accuracy required in Example project was +/- 50mm.  This determined the most suitable flight height.  Drone was suitable and there were no flight restrictions / approvals required.  Drone used was a Mavic 2 Pro and the site area was c.60Acres – with total flight covering 90 Acres.

Step 2 – Prepare Flight Plan

• Flight plan height to be determined, generally this is between 30m and 120m.
• The lower the height the more detail will be captured on the photos – however more photos will be required.  This results in a longer processing time and longer flight time.
•  The Ground Sampling Distance (GDS) is important here – GSD is measured in centimeters per pixel (cm/px) and is the distance between the centre of 2 pixels on the surface.
• Generally between 1cm and 2cm GSD is sought.
• Horizontal accuracy is generally 2 x GSD and Vertical accuracy is generally 3 x GSD.
• We mostly use Pix4D Capture for flight planning.

Project Example – Flight Plan covered c. 90 Acres, flown at height of 119m (AGL).  Flight time was c.31mins (total time 40mins allowing for 1 battery change) and GDS was 3.01cm.

Step 3 – Fly the Site

• Sometimes IAA approval is required (depending on location and height) – we complete the necessary paperwork & submissions on this.  We have extensive experience in this area.
• Safety – Risk assessments are completed.
• The flight plan is uploaded to the Drone and flown.
• Photos are captured in Nadir (90 Degrees facing down) and angled – depending on requirements.
• Images have between 60% and 80% overlap.

Project Example – No external approvals were required.  454 images were taken and processed and mission was complete in 70mins allowing for set up / risk assessments & 1 battery change.

Step 4 – Process the Images

• The images are loaded into Photogrammetry software – such as Pix4D Mapper
• Ground Control Points (GCPs) are added (if necessary – this depends on the drone used and the accuracy required).
• GCPs are usually surveyed using GPS Rover on points identifiable in the photos.  Black/White markers are generally used for this.
• The images are processed and the outputs generated.
• A Ray Cloud and a Point Cloud is produced.

Project Example – 6 GCPs were used to ensure Global accuracy and 2 Check Points were used to measure accuracy.  These were all surveyed with a Leica GPS Rover.

Step 5 – Outputs

• The following outputs are provided;
  • 2D Orthomosaic Photo (corrected for distortion and measurements can be taken directly from this)
  • AutoCAD digitised drawing (site plan) with spot levels as required.
  • Contours showing elevation in relative or actual elevations
  • A 3D computer generated model of the site.

Project Example – See below Typical outputs for this project