A UAV topographic or corridor survey brief needs ten things: the extent as a digital boundary, the purpose, the datum and grid, the RICS accuracy band, the deliverables and formats, the resolution, any existing control or data, access and dates, site constraints, and the reporting cycle. It does not need to specify the aircraft or sensor; the surveyor chooses those to meet the band.
This guide supports our topographic survey and aerial survey services and is the client-side companion to our guide on what a deliverable pack contains.
Why does the brief matter?
The RICS specification Measured Surveys of Land, Buildings and Utilities (RICS, 2014) exists because the brief is where most survey problems begin. A survey scoped to the wrong extent, the wrong band or the wrong grid is not wrong on the day it is delivered; it is wrong on the day the design meets the ground. Ten minutes on the brief saves a re-survey.
What are the ten things?
| # | Item | Why it matters | Example wording |
|---|---|---|---|
| 1 | Extent | Sets the flight envelope, control layout and price; a red-line boundary is rarely enough | ”Survey boundary as attached DWG/SHP on OSGB36, plus a 25 m buffer; include the access road to the public highway” |
| 2 | Purpose | Drives method, band and products | ”Existing-ground base for drainage design and cut-and-fill; DTM under hedgerows required” |
| 3 | Datum and grid | Everything downstream must line up | ”OSGB36 National Grid via OSTN15; levels to ODN via OSGM15” or “Project grid XYZ; grid definition attached” |
| 4 | Accuracy band | The measurable acceptance criterion | ”RICS Band D on hard detail; bare-earth DTM under vegetation reported separately against check points” |
| 5 | Deliverables and formats | Avoids conversion loss and re-issue | ”Orthomosaic GeoTIFF, classified LAS, DTM GeoTIFF and LandXML, 0.25 m contours DWG, surface-feature DWG, accuracy report PDF” |
| 6 | Resolution | Sets flying height and density | ”Orthomosaic ground sample distance not coarser than 3 cm; DTM cell not coarser than 5 cm; contour interval 0.25 m” |
| 7 | Existing control and data | Saves cost and keeps the survey consistent with earlier work | ”Project control schedule attached; previous topographic DWG attached for reconciliation” |
| 8 | Access and dates | Flight windows, possessions and seasons | ”Site available Monday to Friday 08:00 to 16:00; leaf-off capture required for the woodland block; deliverable by [date]“ |
| 9 | Constraints | Known hazards and sensitivities the surveyor must plan around | ”Live 33 kV overhead line along the eastern boundary; public right of way across the south; site is a National Highways scheme” |
| 10 | Reporting cycle | For repeat programmes | ”Weekly epochs for 18 months; volume report within 24 hours of each flight; check points re-observed each epoch” |
1. Extent: what exactly is to be surveyed?
Send the boundary as a digital file (DWG, DXF, SHP or KML), not a screenshot. Say what lies beyond the red line that must still be captured: access junctions and visibility splays, drainage outfalls, grid connection corridors, watercourses to bank top on both sides. On a corridor, state the width either side of the centreline and any spurs. Our DCO-scale survey guide shows how much an envelope grows once every consenting workstream is counted.
2. Purpose: what will the data be used for?
The purpose decides the method. A visual record needs an orthomosaic; a drainage design needs a bare-earth DTM, which under hedgerows means LiDAR; a facade study needs oblique imagery or terrestrial scanning. Say who will use the data and in what software. Our guide on LiDAR versus photogrammetry by ground type explains the trade-offs.
3. Datum and grid: which coordinate system?
For most UK work the answer is OSGB36 National Grid via OSTN15 and Ordnance Datum Newlyn via OSGM15. Large rail and highway schemes often use a project grid with a unitary scale factor so that plan distances are true to the ground. If the project has a grid, attach its definition. If it does not, say so and let the surveyor deliver on the National Grid with the relationship documented. Our OSGB36, OSTN15 and OSGM15 guide covers the choice.
4. Accuracy band: how accurate does it need to be?
State the RICS band, not a bare millimetre figure, because the band carries its own definition of sigma and of hard versus soft detail. Topographic and corridor UAV surveys are normally specified at Band D (±10 mm plan at one sigma) or Band E (±25 mm). Ask for the achieved accuracy to be reported against independent check points. If a tighter band is needed on specific structures, say which, so that terrestrial scanning can be planned for them.
5. Deliverables and formats: what files, in what software?
List the products and name the formats and software versions that will consume them: Civil 3D, MX, OpenRoads, Revit, ArcGIS, QGIS. Ask for a classified point cloud if anyone will model from the data later. Ask for the accuracy report and datum statement as separate items so that they cannot be omitted.
6. Resolution: how fine?
Ground sample distance for the orthomosaic, DTM cell size, contour interval and section chainage interval. On a 250 hectare solar site we delivered a 3 cm orthomosaic, a 5 cm DTM and contours at 0.25 m for planning and 0.5 m for earthworks; on an eroding coastal frontage the monitoring specification was a 10 mm ground sample distance repeated at every epoch. The right numbers come from the purpose.
7. Existing control and data: what is already there?
Attach any project control schedule, benchmarks, earlier surveys, as-built drawings and utility records. Existing control lets the new survey inherit the project datum exactly; earlier surveys let it be reconciled and change reported. If an earlier survey is to be compared with the new one, say so, because the control must then be re-validated rather than simply adopted.
8. Access and dates: when can it be done?
State site hours, escort requirements, induction needs, possession or closure windows and the delivery deadline. State seasonal constraints: leaf-off capture for woodland, low water for a foreshore, outside nesting season where ecology dictates. A fixed-wing platform can capture a large envelope in a short window, but the control network usually has to be established in the same window; the corridor mapping guide explains why.
9. Constraints: what must the surveyor plan around?
List known hazards and sensitivities: live overhead lines, public rights of way, livestock, adjacent aerodromes, a licensed or secured site, a National Highways scheme, plant movements, blasting windows on a quarry. You do not need to explain the approvals these attract; the surveyor manages airspace, site and scheme approvals and will tell you what lead time they carry. What the brief must do is disclose the constraint early enough for that lead time to be planned in.
10. Reporting cycle: is this one survey or a programme?
For monitoring, state the cadence, the report turnaround, the reference surface for volumes and who signs off each epoch. State that check points are to be re-observed every epoch and that any epoch outside tolerance is re-flown before release. Our guide on weekly earthworks monitoring by UAV sets out a working programme.
What should the brief not specify?
The aircraft, the sensor, the number of flights or the flying height. A brief that mandates a multirotor on a 300 hectare site pays for days of unnecessary flying; one that mandates fixed-wing on a building facade asks for something the platform cannot do. Specify the outcome and the band; the surveyor selects the method. Our guide on fixed-wing versus multirotor economics explains the crossover.
How Angell Surveys does this
Angell Surveys is regulated by RICS. We respond to a brief with a proposal that restates the ten items above as we have understood them, names the RICS band we will deliver and verify, lists the deliverables and formats, and sets out the control design and check-point plan before any flying. For a renewable energy developer’s 250 hectare consenting survey, that process produced a single dataset accepted by the Planning Inspectorate, the distribution network operator, the drainage board and the highway authority. For a government client’s coastal monitoring programme, it produced five epochs over three years flown to an identical design so that every surface was directly comparable. Where a brief is incomplete we will say what is missing rather than guess.
Related services
Sources
- RICS, Measured Surveys of Land, Buildings and Utilities, 3rd edition, November 2014: specification template and accuracy band table.
- RICS, Earth Observation and Aerial Surveys, 6th edition, March 2023.
- Ordnance Survey, A Guide to Coordinate Systems in Great Britain, v3.6, 2020.
- Angell Surveys case studies: 250 ha solar farm and BESS, Kirk Michael coastal erosion monitoring, weekly UAV earthworks monitoring.