A complete drone survey deliverable pack contains the orthomosaic, the classified point cloud, the digital terrain and surface models, contours, a CAD drawing of surface features, and an accuracy report that names the datum, the transformation and the independent check-point residuals against the RICS band specified. Before accepting it, check that every file opens on the stated grid and that the report proves the accuracy rather than asserting it.

This guide is written for the person who receives the data: the engineer, project manager or asset owner who has to sign it off. It supports our aerial survey, topographic survey and point cloud survey services.

What should the pack contain?

ItemTypical formatWhat it is forFirst thing to check
OrthomosaicGeoTIFF with world fileBase mapping, GIS overlay, visual recordOpens in the stated grid; no smearing on buildings or lean on tall features (true-ortho)
Classified point cloudLAS or LAZ, E57 for scan dataDesign, clearance, BIM, archive of the raw evidenceClasses present (ground, vegetation, buildings, water); tiled if large
Digital terrain model (DTM)GeoTIFF, ASCII grid, LandXML or TINDrainage, flood modelling, earthworks, design baseBare earth only; no vegetation or vehicles left in it
Digital surface model (DSM)GeoTIFF or ASCII gridLine of sight, visual impact, canopy height, overhead linesFull surface including structures
ContoursDWG, DXF or SHPPlanning drawings, design contextInterval as specified; generated from the DTM, not the DSM
Surface-feature CADDWG and PDFEngineering design and consenting drawing setsLayers to the RICS convention; a layer schedule supplied
SectionsDWG and PDFCorridor design, embankment and platform designChainage interval and scales as specified
Volume reportPDF and spreadsheetEarthworks and stockpile accountingReference surface named and version-controlled
3D mesh or hosted modelOBJ, FBX or browser linkStakeholder review, visualisationGeoreferenced, not just scaled
Accuracy reportPDFProof of fitness for useIndependent check points, RMSE and maximum residual, RICS band, datum statement
Metadata and tile indexXML, SHP, readmeOnward use and audit trailTile index matches the files delivered

Not every project needs every item. A brief should say which are required; our briefing guide covers that.

What must the accuracy report show?

The accuracy report is the only item that tells you whether the rest can be relied on. It should contain:

  • A plan of the ground control points used in the solution and the independent check points withheld from it. If the two are not distinguished, the report is describing internal consistency, not accuracy.
  • The root mean square error in plan and in height across the check points, and the maximum residual. The maximum governs whether the survey is safe to set out from at its worst point.
  • The RICS band the result corresponds to, with the sigma stated. The bands come from Measured Surveys of Land, Buildings and Utilities, 3rd edition (RICS, 2014): Band D is ±10 mm in plan at one sigma, Band E is ±25 mm, Band F is ±50 mm, Band G is ±100 mm. Two-sigma values are double.
  • Hard and soft detail reported separately where the survey includes ground under vegetation.
  • For photogrammetry, the aerial triangulation summary: image count, tie-point statistics, camera calibration and reprojection error. For LiDAR, the trajectory and strip adjustment summary.
  • Flight dates, equipment, processing software and version, and the names of the surveyors responsible.

A report that quotes a single accuracy figure with no check points, no sigma and no band should not be accepted for engineering use.

What should the datum statement say?

Every deliverable should state, in the report and in the drawing title block:

  • Horizontal datum and transformation: OSGB36 National Grid via OSTN15 from GNSS-observed ETRS89
  • Vertical datum and geoid model: Ordnance Datum Newlyn via OSGM15
  • If a site grid is used: its name, origin and scale factor, and how it relates to the National Grid
  • How the control was fixed: OS Net static observation, base station occupation, or existing project control adopted

Our guide on OSGB36, OSTN15 and OSGM15 explains why a survey on the wrong transformation can be metres adrift and still look right.

How do I check each product?

Orthomosaic. Load it over Ordnance Survey mapping or the existing site plan. Kerbs, building outlines and manhole covers should sit on their mapped positions to within the band claimed. Look at tall features: on a true-ortho product the roof and the base of a building coincide; on a standard orthomosaic the building leans.

Point cloud. Open a tile and colour it by classification. Filter to ground only and view it in a hillshade: a good ground class shows terrain, not the outlines of parked plant or hedgerows. Check that the header records the coordinate system.

DTM and DSM. Difference the two. The result should be zero on open hard ground and positive over vegetation and structures; negative values indicate classification errors. Check that DTM contours run smoothly across hedge lines rather than bulging over them.

Contours and CAD. Confirm the contour interval, that levels are in metres to ODN, and that the layer schedule matches the drawing. Spot levels on hard detail should agree with the DTM.

Volumes. Confirm which design or baseline surface the volumes were calculated against, its version and date, and whether bulking or compaction factors have been applied. A volume without a named reference surface is not auditable.

A ten-point acceptance checklist

  1. Every file opens on the stated grid without manual shifting.
  2. The datum statement names OSTN15 and OSGM15, or the site grid and its relationship to them.
  3. The accuracy report separates control from independent check points.
  4. RMSE and maximum residual are stated in plan and height, with the sigma.
  5. The result is expressed as a RICS band that meets or betters the brief.
  6. Soft-detail accuracy is reported separately where vegetation was surveyed.
  7. The point cloud is classified and, if large, tiled with an index.
  8. The DTM is bare earth; the DSM is the full surface; contours come from the DTM.
  9. Volumes name their reference surface and version.
  10. Metadata, flight dates, equipment and software versions are recorded for the archive.

How Angell Surveys does this

Angell Surveys is regulated by RICS and issues every UAV, LiDAR and topographic deliverable with an accuracy report of the form described here, referenced to the RICS band table and the OSGB36 and ODN datum statement. For a water company’s twin reservoir consenting programme the pack ran to a 70 square kilometre classified point cloud and orthomosaic tiled on the 1 km Ordnance Survey grid, with a tile index, ISO 19115 metadata records and a formal accuracy assessment covering the control network, check-point residuals, block adjustment and strip adjustment statistics, so that reservoir designers, hydraulic modellers, ecologists and archaeologists could each load only their tiles. For principal contractors on weekly earthworks programmes the pack is issued within 24 hours of each flight and carries that epoch’s check-point residuals on the front page. Read the Lincs and Fens reservoirs case study and the weekly earthworks monitoring case study.

Sources

  • RICS, Measured Surveys of Land, Buildings and Utilities, 3rd edition, November 2014: accuracy band table and deliverable specification.
  • RICS, Earth Observation and Aerial Surveys, 6th edition, March 2023.
  • Ordnance Survey, A Guide to Coordinate Systems in Great Britain, v3.6, 2020.
  • ISO 19115, Geographic information: Metadata.
  • Angell Surveys guides: UAV survey QA/QC methodologies, OSGB36 drone survey workflows.