Conformance Checking

Conformance checking compares the as-built survey surface against the design surface at specified chainages and lateral offsets along an alignment. SiteView evaluates each point against a configurable tolerance and reports the results with pass, marginal, and fail colour coding — giving you a clear picture of whether your construction meets the design specification.

What Is Conformance Checking?

In road and rail construction, the finished surface must match the design within a specified tolerance. This tolerance is typically defined in the project specification — for example, plus or minus 20 millimetres for a final pavement surface, or plus or minus 50 millimetres for subgrade.

Conformance checking is the process of measuring the as-built surface at defined points and comparing each measurement to the design elevation at the same location. If the difference is within tolerance, the point passes. If it exceeds the tolerance, the point fails and remedial work may be required.

SiteView automates this process by:

1. Computing the design elevation at each check point from the alignment's vertical geometry.
2. Sampling the survey DEM to get the as-built elevation at the same location.
3. Calculating the difference in millimetres.
4. Classifying each point as pass, marginal, or fail based on the tolerance.

ℹ️ Did you know?

Conformance checking in SiteView works with drone survey data (DEMs from photogrammetric processing). For the highest accuracy, ensure your drone surveys are tied to ground control points and processed to a known coordinate system. The accuracy of the conformance results depends directly on the accuracy of the survey DEM.

Running a Conformance Check

To run a conformance check, SiteView needs the following inputs:

Alignment

The alignment defines the centreline and provides the design elevations. Select from the alignments loaded for the current site. LandXML alignments with vertical profiles provide the most accurate design elevations.

Survey

A completed survey with a processed DEM (digital elevation model). The survey provides the as-built ground elevations. The conformance check samples the DEM at each check point to get the survey elevation.

Chainages

The list of chainage values to check. You can specify individual chainages or a regular interval (for example, every 20 metres from 0+000 to 1+500). Each chainage defines a cross-section line perpendicular to the alignment.

Offsets

The lateral offsets from the centreline to check at each chainage. For example, offsets of -6, -3, 0, 3, and 6 metres would check five points across the road width at each chainage — the centreline plus three metres and six metres to the left and right.

Tolerance

The maximum acceptable difference between survey and design elevations, specified in millimetres. Common tolerances include:

• 20 mm — final pavement surface, wearing course
• 30 mm — base course, subbase
• 50 mm — subgrade, general earthworks
• 100 mm — bulk earthworks, rough grading

The default tolerance is 50 mm.

Pass, Marginal, and Fail

SiteView classifies each conformance point into one of three statuses based on the absolute difference between the survey and design elevations:

Pass (Green)

The absolute difference is within the specified tolerance. The as-built surface at this point meets the design specification.

For example, with a 50 mm tolerance, a difference of +32 mm (survey 32 mm above design) would be a pass.

Marginal (Amber)

The absolute difference exceeds the tolerance but is within 1.5 times the tolerance. The point is outside specification but close to the boundary — it may warrant re-measurement or closer inspection.

For example, with a 50 mm tolerance, a difference of -62 mm (survey 62 mm below design) would be marginal (between 50 mm and 75 mm).

Fail (Red)

The absolute difference exceeds 1.5 times the tolerance. The as-built surface at this point is clearly outside specification and remedial work is likely required.

For example, with a 50 mm tolerance, a difference of +95 mm (survey 95 mm above design) would be a fail (beyond 75 mm).

⚠️ Watch out!

A "marginal" result does not mean the point is within specification — it has exceeded the tolerance. The marginal band (1.0x to 1.5x tolerance) is a visual aid to help you distinguish between points that are just outside tolerance and points that are significantly outside tolerance. Always refer to your project specification for the definitive pass/fail criteria.

Results Table

The conformance check returns a results table with one row per chainage/offset combination. Each row shows:

A no data status means the survey DEM did not have coverage at that point — typically because the point is outside the surveyed area.

Click-to-Fly

Each row in the results table includes a position (longitude and latitude) for the check point. Clicking a row flies the CesiumJS camera to that location on the 3D globe, allowing you to visually inspect the area around a failing or marginal point.

This is especially useful for identifying the cause of a conformance failure. Fly to the point, inspect the terrain, check if there is an obvious reason for the discrepancy (a stockpile, an unfinished area, a drainage structure), and decide whether remedial action is needed.

💡 Tip

Start your review by sorting the results table by status to group all fail and marginal points together. Click each one to fly to its location and assess the situation on the ground. This is more efficient than scrolling through hundreds of pass results.

Summary Statistics

At the top of the conformance results, SiteView shows a summary including the alignment name, the tolerance used, the total number of points checked, and the count of pass, marginal, fail, and no-data results. These numbers give you an immediate overview of conformance status for the section of alignment you checked.

Use Case: Road Construction QA

A typical conformance checking workflow for road construction:

1. Define the check parameters — identify the alignment, chainage range, offsets, and tolerance from the project specification.
2. Fly the drone survey — capture aerial imagery over the completed section and process it into a DEM.
3. Run the conformance check — enter the chainages, offsets, tolerance, and select the latest survey.
4. Review the results — if all points pass, the section is compliant. If there are failures, click each failing point to inspect the location.
5. Re-check after remedial work — fly a new survey after corrections and re-run the check to verify compliance.

ℹ️ Did you know?

Conformance checking is complementary to cross-sections. Cross-sections give you a visual profile at a single chainage — useful for understanding the shape of the cut or fill. Conformance checking gives you a systematic pass/fail assessment across many chainages and offsets — useful for formal QA reporting. Use both tools together for a thorough earthworks verification.

Requirements

To run a conformance check, you need an alignment with vertical geometry (from LandXML, or a DXF polyline with Z values), a completed survey with a DEM covering the chainage range being checked, and an appropriate tolerance that matches your project specification.

What's Next?

• Generate cross-sections at specific chainages for visual cut/fill inspection
• Learn about chainage markers for visual alignment reference on the map
• Import alignments from LandXML for full-precision geometry
• Use DXF layer alignments as a quick alternative when LandXML is unavailable