Terrain Analysis Tools — Slope, Drainage, Cut/Fill
Measure slopes, draw cross-sections, estimate earthwork volumes, and visualize drainage — all directly on your modeled terrain.
Terrain Analysis Tools — Slope, Drainage, Cut/FillTerrain analysis in Gardenly3D is available from two places in the terrain workspace HUD:
View tab — always-on overlay toggles that render on the terrain surface:
- Contour Lines (with adjustable interval)
- Slope Heatmap (colour-coded gradient)
- Aspect Arrows (compass direction of surface faces)
- Runoff / Drainage Flow (D8 flow direction arrows)
Analyze tab — interactive point and region tools for specific measurements:
- Spot Elevation — click to read a point elevation
- Slope Callout — click to read slope % and angle at a point
- Profile Line — draw a line to see an elevation cross-section graph
- Region Stats — draw a polygon to see area and elevation statistics
- Cut/Fill — draw a region to calculate earthwork volume against a reference plane
- Break Lines — draw lines to constrain the terrain surface to hard edges (separate article)
All analysis tools are indicative — they reflect the terrain surface as modelled and are designed for design decision-making, not engineering certification.
View overlays — enable from the View tab
Click the View tab in the terrain HUD to access the four overlay toggles:
Contour Lines — click to enable. A slider appears for the contour interval (0.1 m to 5 m). Contours update in real time as you adjust the slider. See the Contour Lines article for full details.
Slope Heatmap — click to enable. A semi-transparent colour overlay appears on the surface:
- Green = flat (0–5° slope)
- Yellow = gentle slope (5–15°)
- Orange = moderate slope (15–25°)
- Red = steep (25°+ slope)
Aspect Arrows — click to enable. Small arrows appear on the surface showing the compass direction each face is oriented toward. Blue = north-facing, orange = south-facing.
Runoff / Drainage Flow — click to enable. Arrows indicate the downhill flow direction water would take across each point of the surface, calculated using the D8 algorithm.
All four overlays can be enabled simultaneously and persist per terrain entity — each terrain remembers its own overlay configuration.
Enable the slope heatmap and contour lines simultaneously for a comprehensive view of the terrain's gradient character — the heatmap shows severity at a glance, and the contour lines show where the gradient concentrations are.
Spot Elevation — read a point elevation
Click Spot Elevation in the Analyze tab to activate the tool. Move the cursor over the terrain surface — a small callout label appears showing the elevation at the cursor position in real time (in meters or feet depending on the project unit setting).
Click to place a persistent spot elevation marker — the callout label remains on the canvas as an annotation. You can place multiple spot elevation markers across the terrain.
To remove a spot elevation marker, click it to select it and press Delete.
Place spot elevation markers at key points — the top of a mound, the base of a slope, a terrace level — to document the design intent and communicate elevations to clients and contractors.
Slope Callout — read slope at a point
Click Slope Callout in the Analyze tab. Move the cursor over the terrain — a callout label shows the slope at the cursor position in two formats:
- Percentage (e.g. 12%)
- Angle (e.g. 6.8°)
Click to place a persistent slope callout marker on the canvas. Multiple slope callouts can be placed.
Slope callouts are useful for checking whether ramp slopes meet accessibility requirements (typically max 5% for wheelchair access), for identifying areas too steep for mowing, or for documenting embankment gradients.
A wheelchair-accessible ramp gradient is typically 1:20 (5%). Place a slope callout on any proposed ramp or sloped path to confirm the gradient meets the brief requirement.
Profile Line — elevation cross-section
Click Profile Line in the Analyze tab. Draw a line across the terrain by clicking a start point and an end point (or click and drag for a straight line).
A profile panel opens showing:
- Elevation graph — the terrain cross-section along the drawn line, with elevation on the Y axis and distance on the X axis
- Minimum elevation along the profile
- Maximum elevation along the profile
- Average slope from start to end
- Total length of the profile line
The graph is interactive — hover over the graph to see the elevation and distance at that point highlighted on both the graph and the terrain canvas.
Multiple profile lines can be placed on the terrain simultaneously. Each appears as a labelled line on the canvas. To remove a profile, select its line on the canvas and press Delete.
Profile lines are excellent for client presentations — they make the designed topography immediately understandable to non-technical clients who find contour maps harder to read.
Region Stats — area and elevation statistics
Click Region Stats in the Analyze tab. Draw a closed polygon on the terrain by clicking to place vertices, then clicking the starting vertex to close the polygon.
A statistics panel opens showing:
- Area of the polygon (in m² or ft² per the project unit setting)
- Minimum elevation within the region
- Maximum elevation within the region
- Average elevation within the region
- Average slope across the region
- Maximum slope within the region
Region stats are useful for characterising areas before deciding on planting or surface treatments — a region with an average slope over 15% may be unsuitable for lawn and better suited to ground cover or hard landscaping.
Draw region stats polygons over proposed planting areas to get an early read on slope character — this informs both plant selection (sun/shade, drainage preference) and maintenance access considerations.
Cut/Fill — earthwork volume calculation
Click Cut/Fill in the Analyze tab. Draw a closed polygon on the terrain over the area where earthwork is proposed.
The Cut/Fill panel shows:
- Reference Plane — a target elevation level. Set this to the finished ground level you are designing toward. The default is the average elevation within the polygon.
- Cut Volume — the volume of earth to be removed above the reference plane (in m³ or ft³)
- Fill Volume — the volume of earth to be added below the reference plane
- Net Volume — the difference between cut and fill. A positive net is a net cut (more to remove). A negative net is a net fill (more to bring in).
Adjust the reference plane elevation using the slider or by entering a value — the cut and fill volumes update in real time.
The cut area and fill area are colour-coded on the terrain:
- Red tint = areas above the reference plane (to be cut)
- Blue tint = areas below the reference plane (to be filled)
For balanced earthwork (minimising material removal and import), adjust the reference plane until the net volume is close to zero — this is the plane where cut and fill balance. A balanced cut/fill design reduces construction cost and environmental impact.
Cut/fill volumes are calculated using prismoidal column integration across the terrain's sampling grid — each grid cell contributes a volume proportional to the elevation difference between the existing and proposed surface. Results reflect the surface at its modeled resolution and are intended for design-stage earthwork estimation, not construction-specification quantities.
Aim for a net cut/fill balance near zero where the brief allows. Balancing cut against fill on-site reduces material haulage, cost, and site disturbance — and it is much easier to discover a large net imbalance at concept stage than during construction planning.
The Cut/Fill tool only compares edit layers against the original base terrain. If your base terrain was imported from a survey file, confirm that the import resolution is sufficient for the scale of analysis needed — coarse grid spacing will understate volumes on steeply varied sites.
Frequently Asked Questions
Do the analysis tools update automatically when I edit the terrain?
Slope callouts and region statistics update if you re-run the tool after editing the surface. The Cut/Fill overlay reflects all currently visible edit layers in real time — switch back into Compare mode after any edit to see updated volumes.
Can I restrict the Cut/Fill calculation to a specific area of the site?
Yes. Draw a Region polygon over the area of interest first, then run the Cut/Fill tool — the volume calculation respects the region boundary and only counts cells inside the polygon. This is useful when only part of the site is being regraded.
How accurate are the cut/fill volume figures?
Volumes are calculated using prismoidal integration at the terrain's grid resolution. They give a reliable indication of earthwork scale and cost for design-stage decisions. For construction-level quantities, use survey data at the appropriate resolution and have the figures reviewed by a qualified civil or landscape engineer.
Can I export the terrain surface and contours?
Yes. The terrain Export dialog outputs the surface as GeoTIFF, OBJ, PLY, glTF binary (.glb), or GeoJSON, and the contour lines as a DXF file. Cut/fill volumes are read from the on-screen summary panel while the Cut/Fill comparison is active. Measurements display in your project's unit system.
Do the overlays and tools work on both imported survey terrain and terrain I built from scratch?
Yes. Every analysis tool and visual overlay works on any terrain surface regardless of how it was created — imported from a DEM/GeoTIFF, traced from survey points, or modeled from scratch using the height-point tools.