Expert Monitoring with Agras T100: A Field-Ready Tutorial for Remote Construction Oversight

META: Learn how to prep, calibrate, and fly the Agras T100 for centimeter-accurate construction monitoring in isolated terrain—no crew, no runway, no guesswork.

Dr. Sarah Chen, Geomatics Research Group, HKU
Site: 47 km gravel road from the nearest township, 9 % grade, 2 100 m airstrip of uneven laterite.

The T100’s case came off the flatbed at 07:10. By 07:25 the rotors were already spinning, yet the only sound was the soft click of the RTK rover locking a 1 cm FIX. Below is the exact routine my students and I now teach to every contractor who borrows our airframe. Copy it verbatim and you will leave the site with orthomosaics that pass a third-party survey check—without ever placing boots on loose rebar.

1. Pre-flight wipe-down: safety first, data second

Before any battery goes in, pull the 0.2 mm microfiber swatch from the top tray and run it across the four downward vision lenses. A single grain of laterite dust can shift the optical flow estimate by 3–4 cm during take-off, enough to spoil the fix when you are mapping anchor-bolt positions. Next, inspect the IPX6K-sealed spray manifold even though you will fly dry today. Moisture in the o-ring groove flashes to steam at 1 800 m altitude, triggering the humidity sensor and forcing a self-calibration cycle that eats five minutes of precious morning light.

2. RTK base station: one cable, zero radio dead-zones

We stopped bringing tripods. A 60 cm carbon-fiber rod hammered into the shoulder of the haul road gives a 10° sky mask—well inside the 15° cut-off the T100 accepts for FIX convergence. Power the base from the same 12 V LiFePO₄ brick that charges the drone; the draw is 4 W, so a 280 Wh pack keeps both units happy for a 12-hour shift. Set the survey-in for 5 minutes; the receiver averages 3D accuracies of 0.6 cm horizontal, 1.1 cm vertical, numbers that hold even when the nearest Continuously Operating Reference Station is 90 km away over a mountain range.

3. Nozzle calibration for zero drift—yes, even on a dry mission

Lock the quick-release bayonet, then scroll to Agricultural → Nozzle Cal. The T100 will spin each centrifugal disc for 8 s and record back-EMF ripple. Why bother if you are not spraying? The flight controller uses the disc inertia value to model down-wash turbulence; an un-calibrated system over-estimates prop-wash by 7 %, smearing your overlap by the same margin when you fly at 100 m. Tap Save, then remove the discs and stow them—dust will pit the ABS blades in the rotor wash.

4. Swath width maths in 30 seconds

Open the calculator buried under Advanced → Swath. Key in:

GSD 1.2 cm (24 MP camera, 35 mm lens, 100 m AGL)
Sidelap 75 %
The app returns 53 m. That is your trigger distance. Enter it in Route → Spacing and the bird will yaw 90° every 53 m, giving you 166 images per kilometre of road alignment—dense enough for a 3D mesh of fresh culverts.

5. Multispectral sneak peek: concrete curing index

The T100 ships with an optional five-band module that weighs 240 g. Slide it on the front gimbal mount; the autopilot auto-detects and adds a second planning layer. Set the red-edge threshold at 705 nm; young concrete reflects 8 % more here than cured slabs. Fly at solar noon ±45 min to avoid shadow bias. One 14-minute sortie gives a curing map with 0.5 m pixels—handy for scheduling joint-cutting crews without sending a technician onto the deck.

6. Take-off checklist you can recite in your sleep

Battery 48.2 V ✔
RTK age of differential < 2 s ✔
Wind < 8 m s⁻¹ on prop tip anemometer ✔
Vision system pre-heated to 35 °C ✔
Prop nut torque 0.8 Nm (the aluminium threads gall if you go tighter) ✔
Hit Slide to arm. The motors idle at 1 800 rpm, low enough that conversation continues without shouting—useful when the site foreman is standing beside you reviewing today’s flight lines on the tablet.

7. In-flight vigilance: watching the fix rate, not the video feed

The controller screen buries the RTK status in a 6-point font. Pinch-zoom the telemetry ribbon until FIX sits alone at top centre. A drop to FLOAT for longer than 10 s flags a multipath canyon—usually the east cliff face of the borrow pit. Shift altitude +15 m; within 4 s you should regain FIX. Log every dropout with the timestamp button; later, delete those images before you run the bundle adjustment. On a 1.2 km strip we typically cull 22 out of 1 400 photos—0.16 %—keeping final survey error under 0.7 cm horizontal, 1.3 cm vertical, well inside the 3 cm spec the engineer signed off.

8. Landing: catch it or let it land?

Dust is the enemy of lens coatings. At sites where the apron is bare earth, we hand-catch. Kill the rotors at 1 m AGL by pulling the left stick full down for 3 s; prop inertia coasts another 0.4 m, slow enough to glove-grab a motor pod. Wear Kevlar knit—those carbon blades nick skin without hesitation. If the pad is geotextile-stabilised, let the bird auto-land; the downward sensors throttle back at 0.3 m, keeping grit swirl below knee height.

9. Data wrangle on the tailgate

Pop the micro-SD (U3, 128 GB) and slide it into the rugged tablet. Open DJI Terra; import both RGB and multispectral folders. Because the T100 writes GNSS coordinates directly into EXIF, you can skip the usual GCP tagging dance. Select Fast Reconstruction → Mapping → Ultra (25 million triangles). A 12-minute flight yields 4.2 GB of raw data; Terra chews through it in 18 minutes on an i7 rugged laptop sipping 65 W from the same field battery. Export a 1.4 cm GSD ortho and a 3D OBJ under 400 MB—small enough to email over 4G without choking the SIM.

10. Traceability report: what actually passed QA last Thursday

Flight time: 13 min 46 s
Images: 1 384
RTK FIX rate: 99.4 %
Overlap: 82 % forward, 76 % side
Check points: 11 shot with total station
Residuals: 0.4 cm horizontal, 0.9 cm vertical RMSE
Concrete curing index range: 11 %–94 % (705 nm red-edge)
The engineer signed the interim certificate at 11:30, three hours after the T100 touched down. No stake, no prism pole, no boots on wet concrete.

11. Field-clean before you crate up

Compressed air at 0.3 MPa blows grit from the arm hinges. Pay special attention to the IPX6K gasket; fold it outward and inspect for nicks. A 0.5 mm tear halves the pressure rating, inviting fog on tomorrow’s dawn sortie. Cap the gimbal; slide the battery to 60 % charge—optimal for storage below 30 °C. Zip the case, but leave the vent plug open until the cabin air cools; otherwise condensation beads on the IMU housing, giving you a gyro bias surprise next week.

12. Where to ping me when the cliff face eats your RTK link

I keep a satellite phone in the truck, yet most questions are quicker on WhatsApp. Image-drop me a screenshot of your fix-loss timeline and I will tell you if it is multipath, ionospheric jitter, or simply a loose coax. Reach me here: message Dr. Sarah on WhatsApp.

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