Geocartis carries out drone surveys of road and highway corridors across India: alignment and topographic survey, monthly construction progress capture for NHAI Data Lake submission, earthwork and quantity measurement, and as-built records at handover. Capture is at 5 cm ground sample distance or better, tied to DGPS ground control along the corridor, with an RMSE report supplied against every dataset. We are based in Ahmedabad and mobilise to project stretches nationally.
We are a survey and geospatial services company. We do not build drones and we do not sell software.
The NHAI requirement, and why it changed the market
In June 2021 NHAI made drone video recording mandatory on every National Highway project, monthly, across development, construction, operation and maintenance. That single decision turned drone capture on highways from a marketing exercise into a contractual obligation with a recurring date attached.
The mechanics matter, because most of the disputes we see come from contractors treating it as a video that somebody uploads rather than as a record with consequences.
Contractors and concessionaires carry out the monthly recording in the presence of the Team Leader of the Supervision Consultant. Comparative videos of the current month and the previous month are uploaded to NHAI’s Data Lake portal, capturing what happened on the project during that month. The Supervision Consultant analyses the footage and comments on it in the digital monthly progress report. NHAI officials then use the same videos during physical inspection to check discrepancies and confirm whether earlier observations have been rectified.
Project Directors carry out monthly drone surveys from the date the contract agreement is signed through to the start of construction, and again on completion. Where NHAI is responsible for operation and maintenance on a developed project, NHAI runs the monthly survey itself.
Here is the part that changes how the capture should be planned. The videos are stored permanently on Data Lake, and NHAI has stated they may be used as evidence in dispute resolution before Arbitral Tribunals and Courts.
A monthly record that will sit in a permanent archive and may be produced in arbitration is a different deliverable from a progress video. It needs consistent flight lines month to month so two epochs can actually be compared. It needs chainage referencing so a frame can be located precisely. It needs a defensible capture date. And in most cases it is worth capturing photogrammetric stills alongside the video, because a video proves what a stretch looked like while a georeferenced surface proves how much material was there.
Most contractors buy the minimum: somebody with a drone who produces a file that satisfies the upload. Three years later, in a claim over embankment quantities or a delay attributed to land handover, that file cannot answer the question being asked. Capturing measurable data at the same time costs marginally more per month and produces a record that can.
Where drone survey fits across a highway project
The corridor is the same. What is being measured changes at each stage.
Feasibility and alignment study
Existing terrain, land use along the proposed corridor, built-up areas, water crossings, existing structures and access constraints. At the option-comparison stage, an orthomosaic and a terrain model over two or three candidate alignments answer questions about cut and fill balance and structure count long before anybody walks the ground.
Detailed project report
This is where honesty is more useful than a sales pitch. NHAI and MoRTH tender documents for feasibility study reports and detailed project reports commonly specify LiDAR-based topographic survey, and the deliverable list usually runs to raw DGPS data for the corridor, point cloud including adjoining areas, a topographic map at 1:1000, contours at a specified interval and cross sections in DWG.
Where a tender specifies LiDAR, photogrammetry alone does not satisfy it, and a provider who tells you otherwise is setting you up for a rejection at technical review. Photogrammetry produces excellent surfaces on open ground and cannot see through the roadside tree cover, scrub and plantation strips that most Indian corridors carry. On DPR-grade work we either deploy LiDAR or we tell you the survey needs a LiDAR partner, and we say which before you engage us.
Land acquisition
Corridor mapping against revenue boundaries supports the 3A and 3D process under the National Highways Act, and gives the competent authority and the Bhoomi Rashi filing a current picture of structures, crops, trees and encroachment within the proposed right of way. The survey does not determine the acquisition boundary, which is a legal process, and it does document what is physically standing inside it on a dated basis.
Pre-construction baseline
The single most valuable flight on the whole project, and the one most often skipped. A full corridor capture before the first machine moves establishes original ground level along the entire alignment. Every earthwork quantity for the rest of the project is measured against it. Where a baseline does not exist, quantities get argued from design sections and borrow pit records, which is how quantity disputes start.
Construction monitoring
The monthly NHAI capture, plus whatever measurement the project actually needs: embankment volumes, cut quantities, borrow area depletion, stockpile positions, structure progress at bridges and interchanges, and traffic management layout at diversions.
As-built and handover
Final corridor capture, as-built geometry against design, drainage and cross-drainage positions, signage and furniture inventory, and a complete orthomosaic of the finished stretch. This is the record the O&M contractor inherits.
Operation and maintenance
Periodic corridor capture for right of way encroachment, median and side drain condition, structure condition at bridges and culverts, and vegetation growth into the clear zone.
How we do it
Corridor survey is a different discipline from block survey, and most of what goes wrong on highway projects comes from treating it as a long thin block.
Step 1: Corridor scoping and chainage
We start from your chainage. Every deliverable we produce is referenced to project chainage rather than to arbitrary tile numbers, because that is how your design, your bill of quantities and your monthly progress report are organised. A cross section at chainage 24+350 needs to be findable at chainage 24+350.
Scoping settles the corridor width, which is rarely just the right of way. Earthwork quantities need the borrow areas. Drainage design needs the catchment beyond the ROW. Encroachment mapping needs a strip outside the boundary. A 40 kilometre stretch surveyed at 200 metres width is a very different job from the same stretch at 500 metres, and the difference is entirely in the flight count.
Coordinate system is settled here too. Most highway projects run on UTM WGS84, and the corridor may cross a zone boundary. India spans UTM 42N to 47N, and a corridor running east to west can cross from one to the next. Deciding to hold a single zone across the whole project, or to split at the boundary, is a decision to make before control goes in.
Step 2: Control along the corridor
Corridors accumulate error along their length in a way blocks do not. A block is constrained on all four sides. A corridor is a long strip with control only along its axis, and the bundle adjustment has much less geometric strength to work with. Left unmanaged, a corridor survey drifts, and the drift is invisible in the deliverable until somebody checks a coordinate at the far end.
We manage that with GCP spacing along the corridor at intervals set by the required accuracy rather than by convenience, with points placed in staggered pairs on alternate sides of the alignment rather than in a single line down the centre. A single line of control down the corridor axis leaves the block free to roll about that axis, which produces a cross-slope error that gets straight into your cross sections.
Independent checkpoints go in at intervals along the length, withheld from the adjustment, and they are how we demonstrate that the far end of the corridor is where we say it is. On long stretches we report RMSE by segment as well as overall, because a single aggregate figure across 40 kilometres can hide a bad section.
Permanent control points are worth establishing on any project that will be surveyed monthly for two years. They are the reason month eighteen can be differenced against month one.
Step 3: Airspace along the length
Block surveys sit in one airspace zone. Corridors do not. A 60 kilometre stretch can start in a green zone, pass within 12 kilometres of an airport perimeter and enter a yellow zone with a lower ceiling, run past a defence installation that puts a segment into red, and cross a district or state boundary that changes who the local coordinating authority is.
We map the whole alignment against the Digital Sky airspace map before quoting and return the zone classification chainage by chainage. Where a segment is unflyable, you know at proposal stage and can plan a ground survey for that section rather than discovering the gap after mobilisation.
Our aircraft carry active Unique Identification Numbers and our pilots hold DGCA Remote Pilot Certificates. Corridor work also runs into the visual line of sight limit: an operation beyond visual line of sight needs specific DGCA permission, so a long stretch is flown as a series of segments with the crew relocating along the alignment rather than as one continuous mission.
Step 4: Flight planning
Ground sample distance is pixel pitch multiplied by flying height divided by focal length. A 20 megapixel one-inch sensor with 5472 pixels across 13.2 millimetres has a pixel pitch of about 2.41 micrometres. With an 8.8 millimetre lens at the 120 metre green zone ceiling, that gives roughly 3.3 centimetres GSD, comfortably inside a 5 centimetre requirement.
Corridor geometry then dictates the flight pattern. We plan a minimum of three parallel strips across the corridor width rather than a single line, because a single-strip corridor has no lateral overlap at all and reconstructs poorly. Forward overlap runs at 80 percent, lateral at 70 percent or higher. Cross-strips go in at intervals perpendicular to the alignment, which is the standard control against longitudinal drift, and they are the first thing a cheap provider omits because they add flight time without adding obvious coverage.
On sections with significant vertical variation, ghat sections, high embankments, deep cuttings and flyover approaches, we plan against an existing elevation model with terrain following so GSD stays inside specification from the cut floor to the embankment crest.
Where structure geometry matters, at bridges, viaducts, interchanges and retaining walls, nadir imagery alone will not reconstruct the vertical faces. Those locations get oblique passes as separate small blocks stitched into the corridor.
Step 5: Capture on a live corridor
Most road survey happens over moving traffic and active construction, which introduces problems a greenfield site does not have.
Moving vehicles produce ghosting in the mosaic and spurious points in the cloud. On a live carriageway this is unavoidable, and it is managed by capture timing and by filtering rather than pretended away. Where the deliverable is a pavement surface model, we schedule for the lowest traffic window the project will allow.
Overhead constraints are the safety issue nobody puts in the method statement. Highway corridors run alongside and underneath transmission lines, and the conductor is often invisible against a bright sky. Every corridor flight plan we produce marks line crossings from the imagery or from the utility drawings, and the crew treats those as no-fly bands at operating altitude.
Site access along a corridor is a logistics exercise rather than a formality. Take-off points need to be reachable, safe and clear of the carriageway, and on a 40 kilometre stretch that means eight to twelve locations identified in advance rather than found on the day.
Where the capture is the NHAI monthly submission, the Team Leader of the Supervision Consultant needs to be present. We schedule around their availability rather than turning up and hoping, because a recording made without them does not satisfy the requirement.
Step 6: Processing
Aerial triangulation with tie point extraction and bundle adjustment against the surveyed GCPs, with camera self-calibration. On corridors we pay particular attention to the distortion model, because uncorrected lens distortion on a long strip produces a systematic vertical bow along the alignment, which reads as a false longitudinal gradient in your cross sections.
Dense matching generates the point cloud. Classification separates ground from vegetation, structures, vehicles and plant. On road corridors the hard cases are the roadside plantation strip, crash barriers and median vegetation, all of which sit close enough to ground level that automatic filters treat them inconsistently. These get checked by hand.
The DTM is then gridded, the imagery orthorectified and mosaicked with seamlines routed away from structures, and contours generated at your specified interval.
Step 7: Chainage-referenced outputs
This is the step that separates a survey deliverable from a set of files. Cross sections are cut at your specified interval, typically every 10, 20 or 25 metres, at right angles to the alignment, and labelled by chainage. Longitudinal sections follow the alignment. Feature lines for carriageway edge, kerb, median, drain invert, toe and crest are extracted as separate CAD layers named to your project convention.
Quantities are computed against the design surface or against the previous epoch, reported by chainage segment so they reconcile against your bill of quantities rather than arriving as a single corridor total that nobody can check.
Step 8: Quality control and delivery
Residuals at the withheld checkpoints, RMSE reported horizontally and vertically, by segment on long corridors as well as in aggregate. The report states control layout, checkpoints held back, processing parameters and software.
Delivery is organised the way the project is organised: by package, by chainage range, and by month where the capture is recurring. Every spatial file carries embedded projection metadata.
Accuracy on a corridor
Ground sample distance and accuracy are different quantities. GSD is the ground area one pixel covers. Accuracy is how close a coordinate is to the truth. On corridors the distinction matters more than anywhere else, because the failure mode is systematic rather than random.
For a well-controlled photogrammetric block, horizontal RMSE typically lands between one and two times the GSD, and vertical between two and three times. At 5 cm GSD that suggests roughly 5 to 10 centimetres horizontal and 10 to 15 centimetres vertical. The figures in your report come from your checkpoints, not from that rule.
What corridor work adds is drift. A block with poor control has error that is roughly uniform. A corridor with poor control has error that grows with distance from the constrained sections, and it grows smoothly, which means it looks entirely plausible. A 40 kilometre stretch can be within tolerance at both ends and 40 centimetres out in the middle, and nothing in the deliverable will show it. This is why we report segment RMSE and why cross-strips and staggered control are not optional extras.
Vertical accuracy drives your quantities. Earthwork volume is area multiplied by height difference, so a systematic 15 centimetre vertical bias over a 40 kilometre corridor at 60 metres formation width represents around 360,000 cubic metres of apparent material. On any project where the survey feeds a payment certificate, that is the number that needs defending.
Two conditions degrade corridor results specifically. Roadside tree cover and plantation strips prevent the ground being seen, so the DTM there is interpolation, and we mark those areas rather than presenting them as measured. Fresh black bituminous surfacing is dark and low in texture, which weakens tie point matching, so newly laid stretches sometimes need additional targets or a lower flying height.
Deliverables and output file formats
| Deliverable | What it is | Format |
|---|---|---|
| Corridor orthomosaic | Georeferenced image of the full stretch, tiled by chainage range | TIFF (GeoTIFF), JPEG |
| Digital terrain model | Bare earth surface for design and earthwork computation | TIFF |
| Digital surface model | Everything captured, including structures, vegetation and plant | TIFF |
| Contours | Generated from the DTM at your specified interval | DXF, SHP |
| Cross sections | Cut perpendicular to alignment at your interval, labelled by chainage | DXF, DWG, PDF, XLSX |
| Longitudinal section | Existing ground profile along the alignment | DXF, DWG, PDF |
| 3D point cloud | Classified, RGB attributed, for design software import | LAS, LAZ |
| Object marking and feature extraction | Carriageway edges, kerbs, median, lane markings, manholes, drains, culvert positions, signage, poles, trees, boundary walls | DXF, TIFF |
| Topographic map | Layered drawing at your specified scale with levels and features | DWG, DXF, PDF |
| Earthwork and quantity report | Cut and fill by chainage segment, against design or previous epoch, base surface stated | PDF, XLSX |
| Change detection surface | Difference between two months, mapped as raster with cut and fill | TIFF, PDF |
| Monthly progress video | Corridor flythrough for NHAI Data Lake upload, comparative with previous month | MP4 |
| Progress photo set | Dated, georeferenced stills at structures and work fronts | JPEG |
| Right of way and encroachment layer | Structures, crops, trees and occupation mapped against the ROW boundary | SHP, DXF, PDF |
| Thermal orthomosaic | Pavement and structure thermal survey where specified | TIFF, JPEG |
| RMSE and quality report | Residuals overall and by segment, control layout, parameters | |
| Flight log and survey record | Flights, heights, times, drone UIN, pilot licence number |
Raw imagery is handed over with the deliverables. On projects where the record may be produced in arbitration years later, holding the raw data yourself matters.
Quantities, billing and the dispute record
The commercial case for drone survey on a road project is not the survey cost. It is the quantity measurement.
Earthwork on a highway package is measured, certified and paid. The traditional method is cross sections at intervals, surveyed by a ground crew, interpolated between. Interpolation between sections at 25 metre spacing on undulating ground introduces error in both directions, and the error is invisible because there is no data between the sections to contradict it.
A surveyed surface removes the interpolation. Cut and fill are computed from measured ground rather than assumed ground, and the figures can be recomputed at any section spacing after the fact because the underlying surface exists.
Three things follow. Borrow area depletion can be tracked directly, which reconciles against material brought to site. Embankment volumes can be measured in layers as they are placed. And where a quantity is challenged, there is a dated surface to point at rather than a set of section sheets and a signature.
The same logic runs through the NHAI monthly capture. A video shows that a stretch was at subgrade level in March. A georeferenced surface shows how much material was in it. When the question in front of an Arbitral Tribunal is which of those two things, having both is materially better than having one.
Beyond national highways
The NHAI requirement drives the market, and most of our road work sits elsewhere.
State highways and PWD roads. Widening and strengthening projects, alignment surveys, and condition mapping for state road development corporations. Requirements vary by state, and we work to the specification in the tender rather than assuming NHAI practice applies.
Rural roads. PMGSY alignment and progress work, where the corridors are short, numerous and often in terrain that makes ground survey slow.
Urban roads and municipal work. Road inventory for municipal corporations, junction improvement design, storm water drainage catchment mapping, road widening against property lines, and utility corridor mapping. Ahmedabad, Surat, Vadodara and Rajkot corporations all run programmes of this kind.
Industrial and private roads. Plant internal roads, port access roads, mine haul roads and township road networks.
Expressway and access-controlled corridors. Greenfield alignments where there is no existing road to survey from and the terrain model is the starting point for everything.
Where we work
We are based in Ahmedabad and mobilise to project stretches nationally. Corridor work means travelling along the alignment rather than to a single site, and our crews are equipped for that.
Gujarat. The Delhi-Mumbai Expressway sections through Vadodara and Bharuch, the Ahmedabad-Dholera Expressway, the Amritsar-Jamnagar Economic Corridor through Kutch and Saurashtra, the Ahmedabad-Rajkot and Ahmedabad-Vadodara corridors, and state highway work across Mehsana, Bhavnagar, Junagadh and Surat. Ahmedabad and Gandhinagar are our base.
Rajasthan and the north-west. Expressway packages through Jaipur, Dausa, Kota, Alwar and Jodhpur, plus corridor work around Udaipur and Bikaner.
Delhi NCR and the north. Ring road and expressway packages around Gurugram, Noida, Faridabad and Ghaziabad, plus corridors through Chandigarh, Ludhiana, Amritsar, Dehradun, Meerut, Lucknow, Kanpur, Varanasi, Prayagraj and Patna.
Maharashtra and the west. Expressway and national highway packages around Mumbai, Pune, Nashik, Chhatrapati Sambhajinagar, Nagpur and Solapur, and coastal highway work through Goa and the Konkan.
Central India. Corridors through Indore, Bhopal, Jabalpur, Gwalior, Raipur and Bilaspur.
Eastern India. Highway and expressway work around Kolkata, Bhubaneswar, Cuttack, Rourkela, Ranchi, Jamshedpur, Dhanbad and Guwahati.
Southern India. Corridors through Hyderabad, Bengaluru, Chennai, Coimbatore, Madurai, Vijayawada, Visakhapatnam, Kochi, Mangaluru and Thiruvananthapuram.
What we do not do
Saying this before you engage us is better than saying it after.
Where a tender specifies LiDAR for DPR-grade topographic survey, photogrammetry does not substitute for it. Roadside tree cover on most Indian corridors makes this a technical limit rather than a procurement preference. We either bring LiDAR to the job or we tell you the survey needs a LiDAR partner.
Network Survey Vehicle work is a vehicle-mounted service and outside what a drone does. Pavement roughness, rutting, texture depth and automated distress classification at traffic speed need an NSV, and NHAI accepts NSV data for exactly that reason. Drone survey and NSV answer different questions and neither replaces the other.
Traffic counting and classification under IRC:SP:19 is a separate discipline with its own duration and station requirements. We do not provide ATCC surveys.
Beyond visual line of sight operation needs specific DGCA permission. Long corridors are flown as segments with the crew relocating, and any provider quoting a 60 kilometre continuous mission without a BVLOS approval is quoting something they cannot legally do.
Setting out and stake-out remain total station work. We survey what exists. We do not mark where things should go.
Frequently asked questions
Is drone survey mandatory on NHAI projects?
Monthly drone video recording is mandatory on National Highway projects across development, construction, operation and maintenance. Contractors and concessionaires carry it out in the presence of the Team Leader of the Supervision Consultant and upload comparative current and previous month videos to NHAI’s Data Lake portal.
What happens to the footage after it is uploaded?
It is stored permanently on Data Lake. The Supervision Consultant comments on it in the digital monthly progress report, NHAI officials refer to it during physical inspection, and NHAI has stated it may be used as evidence in dispute resolution before Arbitral Tribunals and Courts.
Can you do the monthly capture and the measurement in one visit?
Yes, and it is the sensible way to buy it. The video satisfies the upload requirement and the photogrammetric stills produce a measurable surface for quantities. Flying both on the same day costs less than two separate mobilisations and gives you a matched record.
How accurate is a drone road survey?
With correctly spaced and staggered ground control, expect horizontal RMSE around one to two times the ground sample distance and vertical around two to three times. At 5 cm GSD that is roughly 5 to 10 centimetres horizontal and 10 to 15 centimetres vertical. We report measured figures from withheld checkpoints, by segment as well as overall on long corridors.
How much corridor can you cover in a day?
It depends on corridor width, required GSD, airspace and access. A 200 metre wide corridor at 5 cm GSD in a green zone with good take-off access is typically several kilometres a day. Restricted airspace, difficult access and wider corridors reduce that, and we give a chainage-by-chainage plan rather than a single rate.
Can you survey a live highway without closing it?
Yes. Nothing goes on the carriageway. Take-off points sit off the road, and the survey happens overhead. Moving traffic does introduce artefacts, which we manage through capture timing and filtering.
What file formats do you deliver?
Orthomosaic as GeoTIFF and JPEG. DTM and DSM as GeoTIFF. Contours as DXF and SHP. Cross sections and topographic maps as DWG, DXF, PDF and XLSX. Point cloud as LAS and LAZ. Object marking as DXF and TIFF. Quantity reports as PDF and XLSX. Progress video as MP4.
Will your output satisfy a DPR tender?
Where the tender specifies LiDAR, photogrammetry alone will not. Where it specifies drone photogrammetry or leaves the method open, our deliverable set is built to the usual DPR list including 1:1000 topographic mapping, contours, cross sections in DWG and DGPS control data. Send us the tender clause and we will tell you plainly either way.
Do you handle DGCA permissions along the corridor?
Yes. We map the alignment against the airspace map and return the zone classification by chainage, then obtain the permissions each segment needs. Where a segment falls in a red zone, no permission is available and you will know before mobilisation.
Can this month be compared against last month?
Yes, provided both epochs are registered to the same control. On projects running monthly capture we establish permanent control at the outset, which is what allows month eighteen to be differenced against month one and the difference to mean something.
Get a quote for your stretch
Send us the chainage range, the corridor width you need surveyed, the alignment as a KML or shapefile, the deliverables and the frequency. We will return the airspace classification by chainage, the control plan, the delivery schedule and a fixed price.
If the requirement is the NHAI monthly capture, tell us the package name and the Supervision Consultant’s contact, and we will build the schedule around their availability.