Chainage Markers

Chainage is the distance along an alignment from a defined start point, and it is the primary way construction teams reference locations on a road, rail, or corridor project. SiteView displays chainage markers along alignment centrelines on the 3D globe, with configurable intervals and automatic zoom-level density adjustment to keep the map readable at every scale.

What Is Chainage?

Chainage is the cumulative distance measured along the centreline of an alignment from its starting point. It is the standard referencing system used on linear construction projects — roads, railways, pipelines, tunnels, and corridors.

Chainage is formatted as N+MMM, where N is the number of whole kilometres and MMM is the remaining metres within that kilometre, padded to three digits. For example:

• 0+000 — the start of the alignment (zero metres)
• 0+100 — 100 metres from the start
• 0+850 — 850 metres from the start
• 1+200 — 1,200 metres from the start
• 3+045 — 3,045 metres from the start

This notation is universal across the construction industry. When someone says "the defect is at chainage 2+350", everyone on the project knows exactly where that is — 2,350 metres along the centreline from the defined start point.

ℹ️ Did you know?

Chainage always follows the centreline path, including through curves and spirals. It is not a straight-line distance — it accounts for the full geometry of the alignment. On a road with a 500-metre radius curve, the chainage increases along the arc of the curve, not along the chord.

Chainage Markers on the Map

When you toggle an alignment's visibility on in the layer control panel, SiteView renders the centreline as a red polyline on the CesiumJS globe and places chainage markers at regular intervals along it.

Each marker consists of:

• A small red dot positioned on the centreline at the marker's chainage location
• A text label showing the chainage value in N+MMM format (for example, "0+200")
• Labels are rendered with a white fill and black outline for readability against any terrain background

Markers are clamped to the ground surface, so they follow the terrain elevation. Labels scale down and fade out as you zoom further away, keeping the map clean at higher altitudes.

Interval Options

You can configure the chainage marker interval for each alignment independently. The interval determines how frequently markers are placed along the centreline. The available options are:

• 10 metres — the densest option, useful for detailed inspection at close zoom
• 20 metres — the default, a good balance for most road construction projects
• 50 metres — suitable for longer alignments or when you need a less cluttered view
• 100 metres — the sparsest option, useful for very long corridors or overview inspection

To change the interval, use the alignment settings in the layer control panel. The markers regenerate automatically when you change the interval.

💡 Tip

Start with the default 20-metre interval. If you find the markers too dense when zoomed in on a short section, switch to 50 metres. If you need more granularity for precise location referencing, switch to 10 metres.

Zoom-Level Density Adjustment

SiteView automatically adjusts which markers are visible based on how far the camera is from the terrain. This prevents the map from becoming an unreadable wall of labels when you are zoomed out to see a long alignment.

The density rules are:

For example, if you have configured 20-metre markers and you zoom out to a camera height of 3 kilometres, SiteView will only display every 50th metre marker (0+000, 0+050, 0+100, ...) rather than every 20th. When you zoom back in below 500 metres, all 20-metre markers become visible again.

This adjustment happens in real time as you navigate the 3D globe. The camera change listener fires whenever the camera moves by more than 10%, updating marker visibility efficiently.

Marker Interaction

When the alignment is visible on the map, you can interact with chainage markers:

• Visual reference — use the chainage labels to identify locations along the alignment. This is especially useful when discussing defects, progress, or survey points with your team.
• Cross-section at chainage — select an alignment and enter a chainage value in the cross-section tool to generate a cross-section at that location. The chainage markers help you choose meaningful chainages for inspection.
• Conformance reference — when running a conformance check, you specify the chainages to check. The markers on the map help you visualise which chainages have been checked and where the results apply.

ℹ️ Did you know?

Chainage markers are purely visual — they do not affect the underlying alignment data. Changing the marker interval or toggling markers off does not alter the alignment geometry. You can generate cross-sections and run conformance checks at any chainage, whether or not a marker is displayed at that chainage.

Chainage and Elevation

For alignments imported from LandXML files with a vertical profile, the chainage markers carry elevation context. The alignment's vertical geometry allows SiteView to compute the design elevation and design grade at any chainage along the centreline.

This information is used by:

• The cross-section tool — to plot the design elevation profile across the alignment at a given chainage
• The conformance checker — to compare the survey (as-built) elevation against the design elevation at specified chainages
• The alignment polyline — to render the centreline at the correct elevation on the 3D globe

For DXF-derived alignments without a vertical profile, elevation data is limited to any Z values present in the original polyline vertices.

Multiple Alignments

A site can have multiple alignments — for example, a mainline road and several side roads, or a rail corridor with parallel tracks. Each alignment has its own set of chainage markers with independently configurable intervals.

You can toggle individual alignments on and off in the layer control panel to focus on the one you are currently inspecting. The chainage markers for hidden alignments are automatically hidden as well.

⚠️ Watch out!

When multiple alignments overlap or run parallel to each other, their chainage markers can become difficult to distinguish. Toggle off the alignments you are not currently working with, or increase the marker interval on the less important alignment to reduce visual clutter.

What's Next?

• Generate cross-sections at specific chainages to compare survey and design profiles
• Run conformance checks at multiple chainages to verify as-built accuracy
• Learn about LandXML import for full-precision alignment geometry
• Use DXF layer alignments when LandXML files are not available