| **Icon** | **Descriptions** |
| [](https://wiki.app.gridit.nl/uploads/images/gallery/2026-02/calculate-raster.png) | [Calculate raster](#bkmrk-calculate-raster) Calculate the difference between a raster layer and a reference |
| [](https://wiki.app.gridit.nl/uploads/images/gallery/2026-02/calculate-volume.png) | [Calculate Volume](#bkmrk-calculate-volume) Calculate the volume difference between bathymetry layers or against a reference level within defined polygon areas |
The Calculations menu is only available when you have at least one bathymetry layer in your project.
#### 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 current situation |
| Bathymetry layer B | If mode = “layers" this is the reference layer/design |
| 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 |
The Calculations menu is only available when you have at least one bathymetry layer in your project.
**Modes***:*| **Mode** | **Use When** | **Example** |
| Reference Layer | Comparing two bathymetry surveys to detect changes over time or want to calculate volume to meet requirements after erosion | Comparing pre-installation seabed scan with current conditions around monopile foundation. |
| Reference Level | Calculating volume relative to a fixed elevation | Calculating rock dump volume from a fixed level to the top of the rock dump. |
| Layer | How to use |
| Model Layer | This is the baseline to which you will be comparing a design or DTM (digital terrain model) |
| Reference layer | This is normally the design that you will be comparing to the model layer (baseline) |
| Reference level | The depth level in relation to vertical reference that you will compare to the model layer (baseline) |
| **Metric** | **Description** |
|---|---|
| **Model Name** | The model layer that is being used to calculate volume for |
| **Reference Name** | The layer that is being used as the reference for the calculation |
| **Polygon Name** | The area for which volume will be calculated |
| **Volume Above Reference (m³)** | Volume where the model layer is higher than the reference (material addition or accumulation) |
| **Volume Below Reference (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 Reference (m²)** | Surface area where the model layer is above the reference |
| **Area Below Reference (m²)** | Surface area where the model layer is below the reference |
| **Polygon Area (m²)** | The area of the polygon (regardless of whether there is area with or without data) |
| **Area without Data (m²)** | Area inside the polygon which is not covered by the model layer (required to be able to calculate the average layer thickness) |
| **Area without Reference (m²)** | Area inside the polygon which is not covered by the reference layer (required to be able to calculate the average layer thickness) |
| **Average Layer Thickness (m)** | Average heights of the layer that falls withing the polygon (and coverage with data and reference) |
All values are rounded to two decimal places in the output.
**Tips and Best Practices** - **Plan your polygon areas carefully**: Create polygon layers that match your analysis needs before starting calculations. Well-defined areas of interest will make your workflow more efficient. - **Use meaningful layer names**: Name your bathymetry layers with dates or survey identifiers to easily track which data you're comparing. - **Monitor calculation time**: Calculations on large areas or high-resolution data may take some time. The tool displays a loading indicator during processing. - **Export both formats**: Consider exporting both CSV and PDF formats—CSV for detailed analysis and PDF for documentation and reporting. - **Interpret Volume Difference carefully**: Positive values indicate net accumulation; negative values indicate net loss. This metric is particularly useful for quick assessment of material changes. - **Use map highlighting**: Selected polygons are highlighted on the map and automatically centered in the view, making it easy to verify you're analyzing the correct areas. - **Keep data organized**: Maintain a clear naming convention for your surveys and regularly export calculation results to track changes over time. #### Detailed guide The Calculate Volume tool enables you to calculate 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 that define the areas where you want to calculate volumes. - **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?** |
| Reference layer | Use this mode when you want to compare two bathymetric surveys to calculate changes over time or want to calculate volume to meet requirements after erosion. This is ideal for: - Monitoring scour protection settlement or erosion - Comparing pre-installation and post-installation seabed conditions - Tracking sediment accumulation or loss between survey dates - Assessing the effectiveness of remedial work |
| Reference level (m) | Use this mode when you want to calculate volume relative to a fixed elevation value. This is useful for: - Estimating material volume in a rock dump or scour protection layer without requiring a pre-rock dump bathymetry layer - Calculating volume from vertical reference to a specified depth. - Measuring fill or cut volumes against a design elevation |
Important: Once you select a model layer, the tool automatically filters the available reference layers and polygon layers to show only those that are compatible (matching projection and overlapping geographic extent).
**3. Reference Selection** The reference defines what your model layer will be compared against. The reference selection depends on your chosen mode: *For Layers Mode:* Select a **reference layer** from the dropdown. This should be your baseline bathymetry survey, typically an earlier survey that you want to compare against.Only bathymetry layers that have overlapping coverage will appear in this list.
*For Reference Level Mode*: Enter a reference level value in meters. This value represents the elevation you want to use as your comparison baseline. - Positive values: Measure upward from the seabed (e.g., +2.0 meters above the seabed surface) - Negative values: Measure downward from the seabed (e.g., -10.0 meters below the seabed surface) Example: For a scour protection mound where you want to calculate the volume from the top down to 10 meters below the peak, you would enter -10.0 as your reference level. **4. Polygon Layer Selection** Select the feature layer that contains the polygons defining your areas of interest. These polygons specify the area for which the volume calculations will be performed. Only layers containing polygon or closed line string features that overlap with your model layer will be available in the **Polygon layer** dropdown. **5. Polygon Selection** After selecting a polygon layer, choose which specific polygons you want to include in the calculation: - Click the Polygons dropdown to see all available polygons from the selected layer - Select one or more polygons (multi-select is supported) - Use the Select All option to quickly select all available polygons Selected polygons will be highlighted on the map, and the map view will automatically zoom to show all selected areas. do we need to explain what could be the problem if they do not see any polygons (again)? I'm assuming they did not read above. ##### Exporting the results The Calculate Volume tool offers two export formats: **CSV Export** Exports calculation results as a comma-separated values file suitable for: - Import into spreadsheet applications (Excel, Google Sheets) - Further data analysis and processing - Integration with other software tools - Creating custom reports or visualizations **PDF Export** Generates a PDF report with one page per selected polygon, each containing: - A table with all calculation metrics for that polygon - A map view centered on the polygon area with bathymetry data The PDF format is ideal for documentation, presentations, and sharing results with stakeholders who don't need to manipulate the data. **To export:** 1. Click the main export button to use the currently selected format (default is CSV) 2. Or click the dropdown arrow to choose between CSV and PDF formats 3. The file will be automatically downloaded with a filename based on your model layer name ### Common Use Cases