Calculate tools
Overview of Tools
| Icon | Descriptions |
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Calculate the difference between a raster layer and a reference |
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Calculate the volume difference between bathymetry layers or against a reference level within defined polygon areas. |
Calculate Raster
The Calculate Raster tool allows calculations to be made, either between two overlapping bathymetry layers, or between one bathymetry layer and a fixed value. This has many useful purposes, including allowing users to compare original plans with the reality on the seabed.
When a calculation is made, a new layer is created.
All the basic arithmetic operations (add/subtract/divide/multiply/average) are supported.
Options
| Option | Description |
|---|---|
| Mode | Layers Makes mathematical calculations between two bathymetry layers. Fixed value Makes mathematical calculations between a bathymetry layer and a fixed value. |
| Bathymetry layer A | The first bathymetry layer. |
| Bathymetry layer B | If mode = “layers" this is the second layer. |
| Fixed value | If mode = “fixed value" then this is the second parameter in the calculation operation. |
| Operation | Add A + <layer B/value> Subtract A - <layer B/value> Divide A / <layer B/value> Multiply A * <layer B/value> Average (A + <layer B/value>) / 2 |
| Layer | The name of the layer to be created. |
| Personal layer | Only possible for those with a contributor role. Select “Yes" visible to you. |
| Layer group | Place the new layer in this layer group. |
Instruction Video
Calculate Volume
The Calculate Volume tool measures the volume difference between bathymetry layers or against a reference level within defined polygon areas. This is commonly used for monitoring scour protection around monopiles and determining material volume/dredging requirements. The tool outputs into PDF or CSV format.
Quick Start
Prerequisites:
- At least one bathymetry layer loaded in your project.
- One or more polygon features defining calculation area(s).
The Calculations menu is only available when you have at least one bathymetry layer in your project.
Modes:
| Mode | Use When | Example |
| Layers | Comparing two bathymetry surveys to detect changes over time | Comparing pre-installation seabed scan with current conditions around monopile foundation |
| Reference Level | Measuring volume relative to a fixed elevation | Calculating rock dump volume from top surface to 10 meters below the peak |
Basic workflow:
- Select a model layer (the bathymetry layer to analyze)
- Choose calculation mode (Layers or Reference Level)
- Select reference layer (Layers mode) or enter reference level in meters (Reference Level mode)
- Select polygon layer containing your areas of interest
- Choose one or more polygons to calculate volume for
- Click Export to CSV or Export to PDF
Understanding Results:
The volume calculation produces the following metrics for each selected polygon:
| Metric | Description |
|---|---|
| Volume Above (m³) | Volume where the model layer is higher than the reference (material addition or accumulation) |
| Volume Below (m³) | Volume where the model layer is lower than the reference (material loss or erosion) |
| Volume Difference (m³) | Net volume change (Volume Above minus Volume Below). Positive values indicate net accumulation; negative values indicate net loss. |
| Area Above (m²) | Surface area where the model layer is above the reference |
| Area Below (m²) | Surface area where the model layer is below the reference |
| Total Area (m²) | Combined area of all calculated regions (Area Above plus Area Below) |
| Average Layer Thickness (m) | Average depth of change across the total area (calculated as Volume Difference divided by Total Area) |
Detailed guide
The Calculate Volume tool enables you to measure volumetric differences in bathymetric data (bathymetric layers) within specified areas (polygons). This functionality is essential for monitoring seafloor changes, particularly for offshore wind farm applications where scour protection monitoring around monopile foundations is critical.
The tool calculates volumes in cubic meters and areas in square meters, providing detailed metrics including volume above, volume below, and net volume difference for each selected polygon.
Prerequisites
Before using the Calculate Volume tool, ensure you have:
- Bathymetry layers: At least one bathymetry layer loaded in your project. To Layers mode, you need at least two compatible bathymetry layers.
- Polygon layer: A feature layer containing polygons or closed line strings that define the areas where you want to calculate volumes.
- Compatible projections: When using Layers mode, both bathymetry layers must use the same coordinate reference system (projection).
- Overlapping data: The model layer and reference (layer or polygons) must have overlapping geographic extents.
The Calculations menu is only available when you have at least one bathymetry layer in your project.
Configuration
1. Mode selection
| Mode | When to use? |
| Layers Mode |
Use this mode when you want to compare two bathymetric surveys to measure changes over time. This is ideal for:
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| Reference Level Mode |
Use this mode when you want to calculate volume relative to a fixed elevation value. This is useful for:
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2. Model Layer Selection
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3. Reference Selection
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4. Polygon Layer Selection
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5. Polygon Selection