Introduction
Selecting the correct drone to purchase is an important decision to make and what the drone is to be used for needs to be taken into consideration.
DJI have for many years sold dual sensor drones, therefore not just housing an RGB sensor but both an RGB wide/zoom sensors along with a thermal sensor. The packaging of multi sensors into one drone may seem like one drone can be used for all jobs, however, this is not the case.
This article will explain the limitations of the 3 popular drones available (M3E, M3T and M30T) and the products they can be used for when capturing data for Sitemark analysis.
Can one drone be used for high accuracy RGB operations and also Thermography operations?
In short, no.
When flying high accuracy RGB operations, like the Topography and Solar Construction Monitoring a high level of accuracy is needed in the final deliverables. In order to achieve this the RGB sensor needs to be of a high quality.
If RTK is to be used, then the drone needs to have DJI Time Sync to ensure high accuracy photographic locations.
Let's take a closer look at each drone separately.
Drone Comparison
Matrice 30T
Cost: ~11.000€ depending on package purchased
The Matrice 30 and Matrice 30T drones are not designed for surveying. The M30 family of drones is aimed more at the search and rescue and drone in a box services. The thermal camera is ideal for our thermography products along with the RGB sensor to detect anomalies on solar panels.
However, whilst the RGB sensor can be used for thermography operations, it is not of suitable quality for mapping operations, therefore high accuracy using this camera cannot be guaranteed. Also the M30T does not support DJI Time Sync, the DJI Time Sync is required for high accuracy mapping.
Super high resolution is not currently supported by Sitemark. DJI are still to release the Thermal SDK which will allow the processing of the super resolution imagery. More information on this can be found here.
Sitemark recommends that the M30T is only used for its Thermography and Thermography Pro products.
Mavic 3T
Cost: ~7.000€ depending on package purchased
The M3T is a light weight alternative to the M30T for thermography operations. Weighing in at just aver 1KG, this drone is significantly less than the M30T which weighs 3.8KG.
However, the M3T alone is not suitable for high accuracy RGB mapping operations. The RGB sensor on the M3T is different than that on the M3E. The RGB sensor on the M3T is an electrical shutter, whereas the M3E has a mechanical shutter. A mechanical shutter is preferred when carrying out mapping missions as it will yield a higher accuracy deliverable.
More information on mechanical vs electrical shutters can be found on DJI's website here.
Should the M3T be used for Solar Construction Monitoring/mapping/topography operations the accuracy of the data may be ±20cm, however not even this relatively high error can be guaranteed and it could be much greater.
Sitemark recommends that the M3T is only used for its Thermography and Thermography Pro products.
Mavic 3E
Cost: ~5.000€ depending on package purchased
The M3E is a replacement for the long-trusted Phantom 4 Pro RTK and was designed for high accuracy surveying/mapping operations. With its mechanical shutter and high precision camera the M3E provides centimetre accuracy when combined with an RTK solution.
RTK accuracy can be obtained by either purchasing a base station or NTRIP subscription. The DJI D-RTK 2 base station (~3.000€) needs to be set up on a known point, therefore accurately surveyed points need to be set out before the D-RTK 2 base station is setup. Using RTK/NTRIP should negate the need for GCPs, however it is always advisable to set out a couple of GCPs as a way of quality controlling the RTK accuracy obtained by the drone.
Further information on setting up the drone for RTK operations can be found in out support articles here.
Sitemark recommends that the M3E is only used for its Topography and Solar Construction Monitoring products, as it only has an RGB sensor and no thermal capabilities.
Summary
If you are looking for a drone to carryout just thermography operations then either the M30T or M3T will be ideal for you. The M3E is to be used for operations where high accuracy RGB data acquisition is required, therefore Topography of Solar Construction Monitoring operations.
If you have both RGB high accuracy (Solar Construction Monitoring) and Thermography operations then it is more cost effective to purchase an M3T drone dedicated for thermal operations and the M3E for RGB high accuracy operations.