📝 Overview
The Chainage & Offset feature enables you to calculate and place points based on their distance along a line (chainage) and their offset from that line.
This is typically used to enter data located on the ground as distances along a road centre-line and offsets from that centre-line.
⚙️ Start Snap Dialog Options
Within the Start Snap dialog, two options are available:
Calculate from Snap Point – type in chainage and offset values starting from the snapped point.
Calculate from Start of Line – type in chainage and offset values starting from the beginning of the line.
🔄 As chainage can operate in either direction along a line, you may choose to reverse the direction of the chainage:
From the start point, or
From the snapped point, depending on the selected option.
💡 Tip: If the computed chainage lies offscreen, the map automatically scrolls to show the result.
↔️ Offset Behaviour
Offsets are applied relative to the direction of travel along the snapped line:
➖ Negative offset → Positions the point to the left of the snapped line.
0️⃣ Offset = 0 → Places the point directly on the snapped line.
➕ Positive offset → Positions the point to the right of the snapped line.
🔔 Note: If the resultant offset point is offscreen, the map automatically scrolls to centre on the new position.
📐 Visual Offset: Snap to Guideline
Alternatively, offsets may be defined visually using the Snap to Guideline option:
A temporary perpendicular guideline is generated at the chosen chainage.
Select a point along the guideline to define the offset position.
If the selected point is within tolerance of a map feature, you can:
Snap to the intersection of the guideline with that feature, or
Snap to the chosen position (e.g., a lamp column located near a kerb-line).
⚠️ Warning: Ensure your selected offset point is within tolerance — otherwise snapping may not apply.
⚡ Workflow Efficiency
When offsetting from the beginning of a line:
If you snap to the same line again, the snap dialog remembers your previous selections:
Calculate from Start of Line
Snap to Guideline
This allows you to quickly type in the next chainage and define the offset without reconfiguring the dialog.
🛠️ Typical Use Case
The Chainage & Offset feature is most often used to record ground-level asset data, such as:
Street furniture
Utilities
Survey data
All of which are positioned in relation to a road centre-line using chainage and offset measurements.
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