How to choose stockpile surveys in Canada: inventory evidence

Choose a stockpile survey proposal that documents pile coverage, control checks, boundaries and base surfaces—not simply a cubic-metre result. Accepting tonnes also requires independently supported density evidence. [3][4]

Confirm you are procuring a field survey

Ontario Drone Survey describes UAV-based volume calculations; SGS Canada describes laser-based Total Station measurement. These are field-measurement services, distinct from tools for processing or reconciling survey data. [1][2]

• SpeedyDrone Canada: equipment and workflow guidance, rather than an offer to survey your site. [3]
• Birdi: reporting software for calculating, exporting and sharing stockpile volumes. [4]
• Propeller: a measurement and reconciliation platform, rather than a field-survey contractor on its reconciliation page. [5]

SGS supplies a Mississauga, Ontario contact; Ontario Drone Survey’s cited page does not state its service boundary. [1][2] Ask who will attend the site and obtain written confirmation that the field service covers your Canadian location.

Identify every pile and the inventory cutoff

State the intended decision—operations, inventory close, reconciliation or payment—alongside the reviewer and an agreed acceptance tolerance. A drone volume alone does not establish an audited balance, legal boundary or accepted payment quantity. [3]

• Identify the scope: require persistent pile IDs, material, location and responsible contact. Distinguish loose stockpiles, bunker contents and earthwork between dated surfaces. [3]
• Set the inventory moment: specify a cutoff time, not merely a date. Agree how movements will be paused or recorded, with recapture or explicit report restrictions if material moves during capture. [3]
• Align reconciliation records: agree the reporting period and survey, production and sales/dispatch cutoffs so timing gaps are accounted for rather than mistaken for inventory variance. [5]

Check measurement coverage and validation

Drone reconstruction captures visible surface geometry; SGS’s stated Total Station workflow requires the entire pile surface to be visible. Both need documented visibility limits. [2][3]

Ontario Drone Survey describes volume calculations using points in a UAV elevation model for aggregate and other materials. SGS describes calculated stockpile volumes and Civil CAD contour maps, but does not publish a quantified validation result. [2] Request project-specific coverage, visibility exclusions and validation evidence in the proposal. [1]

SGS records laser measurements in a data logger, calculates volume on a PC and generates a contour map using Civil CAD software. Its page describes rapid calculations, including daily provisional reports; that service claim is not an accuracy result for your site. [2]

Ask the surveyor to document equipment, control basis, coordinate and height references, units, independent checkpoints and tolerance. Points used to fit the model are not independent validation of it. [3] Birdi’s accuracy percentages come from third-party material, not validation of a proposed survey. [4]

Require evidence for the base beneath each pile

Volume depends on the measured surface, pile boundary and base beneath it. Require a saved toe polygon tracing where material meets the ground, a named base method and supporting floor evidence. [3]

Ask whether that evidence is accepted empty-pad data, surveyed floor geometry or an approved fitted-surface workflow. A fitted mean plane follows selected measurement points; a lowest-point plane is horizontal through the lowest selected point. Neither recovers an unknown irregular floor. On a sloping pad, the horizontal plane can include space below the pad and overstate material. Require justification against the actual floor, not a method chosen by label. [3]

For merged piles or hidden toes, require documented shared-edge conventions, uncertainty, exclusions and reviewer approval. Request cut and fill separately, with the inventory quantity identified; investigate unexpected fill rather than silently netting it against cut. [3]

Separate cubic metres from supported tonnes

A volume measurement does not establish density: tonnes = cubic metres × loose bulk density in t/m³. The conversion needs independently supported density evidence. [3][4]

Require the density value, material represented, source, test date and any swell or shrink factors. Check whether the evidence represents the material’s relevant condition: moisture, particle size, loading and recompaction can affect density assumptions. [3][4][5]

SGS’s field-service page expressly offers physical density determination using drilling and density-sensing equipment, then uses those data to calculate tonnage. Confirm whether this work is included in the proposal rather than assuming it accompanies the volume survey. [2]

Keep repeat measurements consistent

Retain the same pile-boundary rules, base definition, processing method and density assumptions between periods. Document the reason and expected effect of changes. [3][5] Preserve dated surface models and polygons so reviewers can inspect toe movement and boundary changes. [4][5]

Propeller’s reconciliation starts with surveyed opening inventory, adds production, subtracts dispatches, rehandles and waste, then compares expected closing inventory with surveyed closing inventory. Transfers also belong in the supporting movement records. [5]

Investigate differences separately: reporting cutoffs, density and conversion factors, unrecorded movements, changed boundaries or bases, and processing or sign conventions. Tie each explanation to its supporting record rather than treating the entire variance as material loss. [5]

What to confirm with each provider

Ask Ontario Drone Survey and SGS Canada to confirm prices, minimum terms, cancellation deadlines and refund terms in writing. [1][2] Request a written quote separating included work, optional work and exclusions:

• Scope and charges: site coverage, mobilisation, piles included, control work, density work, deliverable formats, prices and applicable taxes.
• Delivery and changes: turnaround, included revisions, extra processing, return visits and recapture charges.
• Engagement terms: booking lead time, weather postponements, deposits, cancellation and refunds, insurance and personnel qualifications.

Specify who authorises additional work and how costs will be approved before it proceeds.

Accept the evidence pack, not just the number

Make the evidence pack a written acceptance condition. [3] Require:

• Pile/site IDs, capture date, inventory cutoff, measurement method and units. [3][4]
• Surface model or contour evidence, supporting visuals and saved pile boundaries. [3][4]
• Base method, supporting floor evidence and visibility exclusions. [3]
• Control and independent-check results, plus preparer and reviewer identification. [3][4]

Specify handover files: capture and positioning records, coordinate metadata, processing/software version, agreed model exports and review history. [3][4] For reconciliation, add sourced density and conversion factors, book-data records and export dates, cutoff confirmation, and second-person review. [5]

Agree how surface/toe coverage, model quality, independent checks and base evidence will be assessed against the project tolerance. Record the outcome as accepted, provisional or withheld, identifying missing evidence and corrective action. [3] Assign reconciliation actions an owner and due date. [5] A provisional operational estimate should not become a payment or accounting quantity without the missing acceptance evidence. [3]

References

1. Volume Calculations – Ontario Drone Survey (ontariodronesurvey.ca)
2. Stockpile Inventory Measurement | SGS Canada (sgs.com)
3. Stockpile Volume with Matrice 4E & DJI Terra | Canada | SpeedyDrone Canada (speedydrone.ca)
4. Birdi Blog: How to create a stockpile volume report (birdi.io, 2026)
5. Stockpile Reconciliation: Understanding the Basics – Propeller (propelleraero.com)