Design Comparison
Cross-Section vs Design
The Cross-Section vs Design tool draws a survey profile line and overlays the design profile on the same chart, showing you exactly where cut and fill occur along any section line through your site. It is especially useful for visualising earthworks progress at specific locations.
![[Screenshot: Cross-section chart showing a survey profile line (solid) and design profile line (dashed) with red shading for cut areas and blue shading for fill areas, plus an area statistics summary]](/images/placeholder.png)
How It Works
The cross-section tool samples elevation data along a line you draw on the map. When a design surface is selected, the tool samples both:
- Survey profile — elevations from the DEM along the section line
- Design profile — elevations from the design surface along the same line
Both profiles are plotted on an SVG chart so you can visually compare them side by side.
Drawing a Section Line
- Open the Cross-Section measurement tool from the toolbar.
- Select a design surface from the dropdown to enable the design overlay.
- Click a start point on the CesiumJS map.
- Click an end point to complete the section line.
The section line appears on the map as a straight line between your two clicked points, and the profile chart opens in the panel.
💡 Tip
For the most useful cross-sections, draw your line perpendicular to the direction of earthworks. On a road project, draw sections across the road corridor. On a dam or embankment, draw sections across the fill profile.
Reading the Profile Chart
The SVG chart displays elevation on the vertical axis and distance along the section line on the horizontal axis.
Profile Lines
| Line | Style | Represents |
|---|---|---|
| Survey profile | Solid line | Current terrain elevation from the DEM |
| Design profile | Dashed line | Target finished level from the design surface |
Cut and Fill Shading
Where the two profiles differ, the area between them is shaded:
- Red shading — cut areas where the survey surface is above the design surface (material needs to be removed)
- Blue shading — fill areas where the survey surface is below the design surface (material needs to be added)
The shading makes it immediately obvious where work is required and how much material needs to move.
Area Statistics
Below the chart, the tool displays area statistics for the cross-section:
| Statistic | Description |
|---|---|
| Cut area | Total cross-sectional area of red (cut) zones, in square metres |
| Fill area | Total cross-sectional area of blue (fill) zones, in square metres |
| Net area | Cut area minus fill area |
| Section length | Total length of the section line |
ℹ️ Did you know?
Cross-section areas are two-dimensional (square metres), not volumes. To estimate a volume from cross-sections, you would take multiple parallel sections and use the average end-area method. For direct volumetric calculations, use Compare to Design Volume instead.
Chart Interaction
The profile chart supports several interactions:
- Hover — move your cursor along the chart to see the exact elevation values for both survey and design at any point, plus the difference
- Zoom — scroll to zoom into a portion of the chart for closer inspection
- Pan — click and drag to move the visible area when zoomed in
- Reset — double-click to reset the chart to its full extent
Vertical Exaggeration
By default, the chart uses vertical exaggeration to make elevation differences more visible. The exaggeration factor is shown on the chart and can be adjusted. At 1:1 scale, the chart shows true proportions, which can make subtle grade differences difficult to see.
Multiple Sections
You can draw additional section lines without clearing previous ones. Each section generates its own profile chart. Use this to build up a set of cross-sections at regular intervals along a corridor or across an earthworks area.
💡 Tip
On road projects, take cross-sections at regular chainage intervals (e.g., every 20 metres) to build a comprehensive picture of earthworks progress. If your site has alignments loaded, you can also use the Cross-Sections at Chainage tool to generate sections automatically along an alignment.
Saving and Exporting
Cross-section measurements are saved to the site's Measurements tab with the profile data and area statistics. You can:
- View on Map to return to the section line and profile chart
- Export as PDF with the profile chart and statistics — see PDF Reports
- Export as CSV with the profile data points — see CSV Export
What's Next?
- Compare to Design Volume — calculate cut and fill volumes within a polygon boundary
- Grade Check vs Design — check individual point elevations against the design
- Cut/Fill Heat Map — generate a colour-coded overview of earthworks across the site
- Cross-Section (Measurement Tool) — the standalone cross-section tool without a design overlay