Earthwork Volumetrics with Drones — Beating Truck Counts
Introduction
Truck counts are slow, error-prone, and hard to defend when money’s on the line. Meanwhile, dozers keep moving dirt, stockpiles grow and shrink, and pay apps need real numbers—now. Drone-based volumetrics solve this by turning a short flight into precise, auditable measurements for cut/fill and stockpiles. With the right workflow (RTK/PPK + checkpoints) you get engineering-grade data that aligns with CAD and stands up in meetings with owners.
In this guide, you’ll learn how drone volumetrics work, where they beat traditional methods, and the best practices that separate “good enough” from defensible.
Why Truck Counts Fall Short
Truck counts seem simple—until you ask a few questions:
Variable load factors: Moisture, compaction, and material behavior swing weights and volumes day to day.
Uncertainty in struck vs. heaped loads: What’s “full”? Who decides?
Human error: Missed loads, double-counts, long days, inconsistent recordkeeping.
No spatial context: Even if counts were perfect, you can’t tell where material moved or verify toe lines on stockpiles.
Drone volumetrics sidestep these issues by measuring the material where it sits, comparing accurate surfaces (pre/post), and producing repeatable results with a clear audit trail.
How Drone Volumetrics Work (Plain English)
1) Capture
Fly the site with a mapping drone (RTK/PPK recommended).
Collect nadir images at high overlap (typically 75–80% front/side).
For steep piles or complex shapes, add a quick oblique pass.
2) Reconstruct
Software converts images into a point cloud and surface models (DSM/DTM).
Surfaces are georeferenced in your project coordinate system.
3) Compare Surfaces
Cut/Fill: Subtract current surface from design grade (or from a previous capture) to compute material removed/placed.
Stockpiles: Define the toe (base boundary), then compute volume above that base plane or base surface.
4) Report
Output volumes by area, delta maps, and color-coded cut/fill visualizations.
Export PDF summaries and CAD-ready files for the owner’s package.
Where Drones Win
1) Speed & Cadence
A 20–40 acre site can be flown in under an hour and processed the same day—fast enough to align with weekly pay apps or post-storm checks.
2) Accuracy You Can Defend
With RTK/PPK and a few checkpoints, volumetrics typically reach low single-digit percent error when piles are well-captured and toes are clearly defined. That’s more consistent than “eyeballing” loads.
3) Visual Proof
Colorized cut/fill maps and 3D views end arguments. You’re not debating a clipboard; you’re reviewing measured surfaces.
4) Safety
Fewer folks scrambling up steep piles or trying to read a pile’s shape from the ground. Capture from above, safely.
RTK/PPK, GCPs & Checkpoints — What You Actually Need
RTK/PPK: Use it. It stabilizes absolute positioning and improves vertical accuracy.
GCPs (Ground Control Points): Not always required if RTK is solid, but…
Checkpoints: Always place 1–3 independent checks (AeroPoints or surveyed nails). They verify your accuracy report and give confidence in pay apps.
Coordinate System: Agree on project CRS (e.g., State Plane + GEOID for elevations) before you fly.
Rule of thumb: RTK + checkpoints delivers consistency and a clean RMSE report your owner or engineer can trust.
Best Practices for Stockpile Surveys
1) Plan the Flight for Shape
Altitude: Low enough to hit your GSD target (e.g., 2–3 cm/px), high enough to keep coverage efficient.
Overlap: 80/80% for complex piles; 75/75% for simple terrain.
Obliques: One quick ring around tails and steep sides improves reconstruction substantially.
2) Define the Base Correctly
Toe Lines: Draw tight, accurate toes; volume swings wildly when the base is sloppy.
Base Plane vs. Base Surface:
Plane is fine for clean, flat ground.
Surface is better on uneven subgrade.
3) Avoid Problem Lighting
Harsh shadows and low sun exaggerate pile edges and cause noisy point clouds.
Midday or bright overcast is ideal.
4) Keep People & Equipment Clear
Moving equipment creates ghost geometry. Pause operations for a quick flight if possible.
Best Practices for Cut/Fill
1) Capture Before & After
Compare current surface to design surface (for target completion) or to previous as-built (for incremental progress).
2) Lock Your CRS & Vertical Datum
Misaligned vertical datums = bogus cut/fill. Confirm GEOID with your surveyor.
3) Segment by Area
Break big sites into logical zones (pads, roads, utilities) so PMs can reconcile line items.
4) Sanity Check with Ground Truth
Use checkpoints or quick rover shots to validate elevation residuals.
Workflow: From Flight to Pay App (Step-by-Step)
1) Pre-Flight
Confirm CRS, GEOID, and RTK/PPK method.
Place 1–3 checkpoints.
Check wind, lighting, and airspace (LAANC if needed).
2) Flight
Nadir grid, 75–80% overlap.
Add obliques on steep piles.
Keep altitude consistent; log everything.
3) Processing
Calibrate with RTK/PPK corrections.
Clean point cloud (remove machines/crew if needed).
Generate DSM/DTM, contours, orthomosaic.
4) Volume Computation
Draw toes; choose base method (plane or surface).
Compute volumes and cut/fill by zone.
Export reports and CAD layers.
5) QA/Accuracy
Produce accuracy report with RMSE and checkpoint residuals.
Visual spot-check: do the numbers match site reality?
6) Delivery & Reconciliation
PDF summary for owners.
CAD deliverables for engineers (DXF/DWG/CSV).
Map changes to pay app line items.
Common Pitfalls (and How to Avoid Them)
Loose Toe Lines: Sloppy digitizing = inflated volumes. Slow down and zoom in.
Wrong Vertical Datum: The fastest way to nuke trust. Align on GEOID once—document it.
Shadows & Low Sun: Leads to “lumpy” models. Shift the flight window.
No Checkpoints: You can’t defend the results without independent checks.
Piles Against Walls/Conveyors: Add obliques; if needed, supplement with hand shots or lidar for tight edges.
Expected Accuracy (Realistic, Not Hype)
When flown and processed correctly, stockpile volumes and cut/fill calculations can reach low single-digit percent error on well-defined piles and clear bases. Terrain complexity, vegetation, reflections (snow/water), and poor lighting can widen that margin. The key is to document your workflow and include checkpoints so the story is transparent.
Deliverables Owners Expect
PDF Volume Report: Totals by pile/zone, with date/time stamps.
Cut/Fill Map: Colorized raster with legend; easy for meetings.
Orthomosaic: High-res georeferenced TIFF + a PDF for quick viewing.
Contours & Surfaces: DWG/DXF/SHP, plus CSV if they want raw tables.
Accuracy Report: RMSE, checkpoints, coordinate system notes—non-negotiable for defensibility.
Integrating with Project Platforms (Procore/BIM/Shared Drives)
Store PDFs in Procore under your standard “Survey/Imagery” folder.
Keep naming conventions consistent (e.g.,
YYMMDD_Project_Area_Volumes.pdf).Maintain a version log so teams can trace which surfaces were used for a given pay app.
Mini Case Scenarios
#1: The Mysterious Missing Yards
An owner challenges a pay app citing truck counts. Your drone report shows +/- 2% change in pile volume across three areas, with a clean accuracy report and toe definitions. Dispute resolves in one meeting—no re-measure needed.
#2: Post-Storm Reality Check
A summer storm erodes a roadway subgrade. Next-day flight quantifies material loss along the corridor; crews target only the true deficit. The before/after comparison preserves schedule and focuses labor.
#3: Closeout Confidence
At project closeout, drone surfaces align with as-builts; the owner gets a final cut/fill package and orthos for records. No ambiguity at handoff.
FAQ (Short & Practical)
Do I really need RTK?
If you’re doing volumetrics or elevation-sensitive work, yes—RTK/PPK reduces vertical drift and keeps surfaces aligned to CAD.
How often should we fly?
Earthwork-active sites: weekly or biweekly.
Stockpiles: after major changes or at each pay app cycle.
Stormwater events: post-storm verification flights.
What if piles are near buildings or conveyors?
Add obliques and, if necessary, supplement with ground points. Clear toe lines are everything.
