Mapping & Modelling – Aerial Mapping​

Remember:​

Role Equipment is the equipment required to perform a role!​

RGB Cameras (normal cameras)​

Typical images (can be used to survey/reconstruct objects)

Multi-/Hyper-spectral Cameras​

“Images” but in different bands that we can’t see (infrared, ultraviolet, etc.; Can be used to identify plants, check plant health, see stress fractures in buildings, etc.)​

Radar/Lidar​

Collect distance measurements (radar: long range, but large “sample area”; lidar: short range, “point sample”; can be used to create highly accurate 3D reconstructions)

Cameras are the most common types of mapping payload.

Features of a camera:​

• Image Sensor:​

• Image Sensor:​
  • Resolution (pixels height & width: e.g. 6000×4000, example: flower (high/low))​
  • Size (size of sensor in mm)​
• Shutter Speed (stills) / Frame Rate (film): the faster cruise speed, the quicker the shutter must be (other wise you will get blurring, example: waterfall (quick/slow))​
• Focal length: determines the amount of zoom (in combination with sensor size)

There’s (technically) no such thing as “zoom”!​ Increasing focal length has the “effect” of zooming in​.

You can’t get a x16 zoom lens, as it depends on your camera’s sensor size!​ The reason there is no such thing as “zoom” is because there’s no standard “1x” zoom. You can have a zoom factor, which is:

[zoom factor] = [focal max] / [focal min]​

Field of View:​

​For A6000 with 16mm lens:​

• FOV (W) = 2 x arctan(23.50/(2×16)) = ~73°​
• FOV (H) = 2 x arctan(15.6/(2×16)) = ~52°​

Ground resolution determines how much detail is captured during a survey or mapping mission:

• R_G: Ground resolution (meters / pixel)
• θ: Field of View
• h: Altitude (meters)
• n: number of pixels

R_G will be the same for height and width…
… Because pixels are square, check the math!

“Photogrammetry is the science and technology of obtaining reliable information about physical objects and the environment through the process of recording, measuring, and interpreting photographic images.”

This means we can collect images, then actually do something useful with them!

• Survey ground levels…
• Check crop growth…
• Perform building inspections…
• …and so much more!

Area scanning typically uses a survey grid:

• Usually referred to as a “lawnmower pattern”
• During planning, it’s good to start at the opposite end from your take-off…
• Why do you think this is the case?

The total flight time for any survey depends on the:

• Total number of passes
• Aircraft cruise speed
• Size of the area surveyed

The camera parameters we use have a big impact on the flight plan we create!

• Focal length and Ground Resolution give use the altitude to fly at
• Overlap and Sidelap is required to match features in photos
  • Usually 50-80% is required
  • More Overlap means more photos
  • More Sidelap means more passes
• Depending on the object surveyed, we also might need multiple angles!

On the left (could be):

• Lower altitude
• Longer focal length
• More overlap/sidelap

On the right (could be):

• Higher altitude
• Shorter focal length
• Less overlap/sidelap

We must follow all previously discussed regulations!

§Privacy Act 1988 (Privacy Act):

• Get consent: Tell anyone that you plan to photograph that their image will be captured before it is captured.
• Store securely: Make sure recorded personal information is secure and destroyed or de-identified when it is no longer needed.

The Privacy Act does not apply to individuals acting in a private capacity (non-commercially)