Cross-Sections

Cross-sections let you slice through the terrain at any chainage along an alignment and see the elevation profile from left to right across the centreline. SiteView generates an SVG chart showing the survey surface and design surface side by side, making it easy to identify cut and fill areas and verify earthworks progress.

What Is a Cross-Section?

A cross-section is a vertical slice through the terrain, taken perpendicular to the alignment centreline at a specific chainage. It shows the ground elevation profile from one side of the corridor to the other — typically a set distance left and right of the centreline.

In construction, cross-sections are a fundamental tool for earthworks quality assurance. They show exactly where the ground is above the design (material to be cut) and where it is below the design (material to be filled). By comparing cross-sections at multiple chainages along an alignment, engineers can track earthworks progress, calculate volumes, and verify that the finished surface meets the design within specification.

Generating a Cross-Section

To generate a cross-section in SiteView:

1. Activate the Alignment Cross-Section tool from the measurement toolbar.
2. Select an Alignment from the dropdown — this lists all alignments loaded for the current site.
3. Optionally select a Survey — if a completed survey with a DEM is available, the survey elevation will be plotted alongside the design.
4. Enter the Chainage value in metres — the point along the alignment where the cross-section will be cut.
5. Set the Half-Width — how far left and right of the centreline to sample (in metres). The default is 15 metres, giving a 30-metre total cross-section width.
6. Click Generate to compute the cross-section.

SiteView sends the chainage and half-width to the server, which computes the perpendicular cross-section line at that chainage using the alignment's horizontal geometry, samples both the survey DEM and the design surface along that line, and returns the elevation data for charting.

💡 Tip

The chainage value does not need to match an existing chainage marker. You can enter any chainage within the alignment's range — for example, 0+137.5 — and SiteView will compute the cross-section at that exact location. Use the chainage markers on the map as a visual guide for choosing meaningful chainages.

The Cross-Section Chart

The cross-section is displayed as an inline SVG chart within the tool panel. The chart shows:

Survey Profile (Amber Line)

The solid amber line represents the as-built ground surface from the survey DEM. This is the actual terrain elevation sampled at points along the cross-section line. If no survey is selected, this line is not shown.

Design Profile (Dashed Blue Line)

The dashed blue line represents the intended design elevation from the alignment's vertical geometry and any associated design surface. For LandXML alignments with a vertical profile, the design elevation at the centreline comes from the vertical geometry. For the full cross-section width, elevations are sampled from the design surface if one is available.

Centreline Marker

A vertical dashed grey line labelled "CL" marks the centreline position in the chart. The horizontal axis extends from negative half-width (left of centreline) to positive half-width (right of centreline).

Elevation Axis

The vertical axis shows the elevation range in metres, auto-scaled to fit the data. The minimum and maximum elevation values are labelled on the axis.

Cut and Fill

The relationship between the survey profile and the design profile reveals where earthworks are needed:

• Cut — where the survey (amber) is above the design (blue). Material needs to be removed to reach the design level. In the chart, this appears as the amber line sitting above the blue dashed line.
• Fill — where the survey (amber) is below the design (blue). Material needs to be added to reach the design level. This appears as the amber line sitting below the blue dashed line.

The statistics panel below the chart shows the Design RL (reduced level — the design elevation at the centreline) and the Max Cut value, which is the greatest vertical distance where the survey surface exceeds the design surface across the cross-section.

ℹ️ Did you know?

Cross-sections are a snapshot at a point in time. As earthworks progress and new surveys are flown, you can regenerate cross-sections with the latest survey data to track how the ground is progressing towards the design. Compare early surveys to later ones to verify that cut and fill operations are being carried out correctly.

Navigating Between Chainages

The cross-section tool includes Prev and Next buttons for stepping through chainages along the alignment. Each click moves the chainage forward or backward by the step interval (20 metres by default) and automatically regenerates the cross-section.

This makes it easy to walk through the alignment chainage by chainage, inspecting the survey-to-design relationship at each point without manually entering values.

The chainage is clamped to the alignment's range — you cannot step before the start chainage or beyond the end chainage.

💡 Tip

Use the Prev/Next buttons to quickly scan through an alignment looking for areas with significant cut or fill. When you spot a section that needs attention, note the chainage for follow-up in the field. You can also reference these chainages when running a full conformance check.

Half-Width Configuration

The half-width setting controls how far the cross-section extends on each side of the centreline. The value is in metres, and it applies equally to both sides.

Adjust the half-width to match the width of your construction corridor. If the cross-section is too narrow, you will miss the batter slopes on either side. If it is too wide, the vertical scale will be compressed and small differences between survey and design will be hard to see.

Requirements

To generate a cross-section, you need:

1. An alignment — either a LandXML import or a DXF layer alignment.
2. A completed survey with a DEM (optional but recommended) — the survey provides the as-built ground surface. Without a survey, only the design profile is shown.
3. A design surface (optional) — for cross-section elevations away from the centreline, a design surface DXF or TIN is needed. The alignment's vertical profile provides the centreline design elevation, but lateral design elevations require a separate design surface.

⚠️ Watch out!

If neither a survey nor a design surface is available, the cross-section tool has no elevation data to display. Ensure you have at least one data source — a survey DEM for the as-built profile, a design surface for the design profile, or ideally both for comparison.

Using Cross-Sections for Earthworks QA

Cross-sections are a core tool in the earthworks QA workflow:

1. Before earthworks begin — generate cross-sections from the initial survey to understand the existing ground conditions and estimate cut/fill quantities.
2. During earthworks — fly regular drone surveys and regenerate cross-sections to track progress. Verify that the contractor is cutting and filling to the correct levels.
3. On completion — generate final cross-sections from the as-built survey and compare against the design. Use these alongside conformance checks to confirm the finished surface is within specification.

What's Next?

• Run conformance checks at multiple chainages to verify pass/fail status against tolerance
• Review chainage markers on the map for visual alignment reference
• Import alignments from LandXML or DXF layers