Considerations for Conducting Separate IR and RGB Flights

Capturing RGB/IR imagery simultaneously with a dual payload is the preferred data capture method. However, it is possible to capture IR and RGB data in separate flights using different drones/sensors rather than using a single drone with a dual (IR/RGB) camera. Raptor Maps requires RGB and IR imagery (inspection level and obliques) to be captured on the same day. If a solar site is too large to capture in a single day, the pilot can break the site up into sections, ensuring that RGB and thermal imagery (including obliques) are captured on the same day for each section.

Altitude will need to be adjusted for each flight to capture the required Ground Sample Distance (GSD) given the specific sensor and inspection level of the flight. GSD requirements for thermal and RGB imagery for each inspection level are listed below. Thermal (IR) imagery must be RJPEG (the Zenmuse XT has an option for RJPEG and JPEG – ensure RJPEG is selected). RGB imagery must be JPEG. All imagery must contain metadata (GPS, relative altitude, gimbal altitude, and timestamp).

Thermal Imagery

Supported Drones and Thermal (IR) Sensors

M210 Compatibility

If using the DJI M210 (or M210 RTK) dual gimbal with separate IR/RGB sensors, DJI Ground Station Pro will only capture imagery from slot 1. GS Pro will not simultaneously capture imagery from sensors in slot 1 and 2. The pilot will have to conduct separate IR/RGB flights and ensure the sensor is mounted in slot 1 for each flight. The following image shows where slot 1 and slot 2 are labeled on the M210 dual gimbal mount.

Visible (RGB) Imagery

Supported Drones & RGB Cameras

Calculating GSD or Flight Altitude from GSD

To calculate GSD or calculate altitude to obtain a certain GSD, you will need to know the following variables.

Sensor height (millimeters)
Sensor width (millimeters)
Image height (pixels)
Image width (pixels)
Focal length of the sensor (millimeters)
Flight altitude (centimeters) – if calculating GSD
GSD (cm/pixel) If calculating altitude for a given GSD

GSD Equations:

GSDh = flight altitude x sensor height / focal length x image height
GSDw = flight altitude x sensor width / focal length x image width

Whichever value is larger (GSD height or width) will be the functional GSD to account for the “worse” resolution of the two.

GSD Calculators

There are several open-source GSD calculators which allow you to select from a preset list of drones/payloads or manually enter the variables necessary to calculate GSD. Here is a non-exhaustive list of GSD Calculators:

Propeller
Handal Selaras
HeliGuy
Pix4D (Downloadable .xlsx/.ods format)