Disclaimer: Nearmap provides the volume estimation tools as a general reference source only. Before relying on any volume estimation information, you should independently verify its accuracy, currency, completeness and relevance, and obtain any appropriate professional advice relevant to your particular circumstances and purpose.

The volume estimation information provided is current as at the publication date only, and as a Product under the Nearmap Agreement is subject to the limitations of liability and other terms set out in the Nearmap Agreement.

# Using the Nearmap Volume Tools

The Nearmap MapBrowser has three tools for estimating volume:

- Pit tool - estimates the volume of a user-defined pit.
- Mound tool - estimates the volume of a user-defined mound.
- Excavation tool - estimates the volume that would be excavated from a user-defined excavation site.

This guide includes the following sections:

The tools are available from the **Volume** icon on the Nearmap toolbar:

All three of these tools use our elevation data to make volume estimates.

Heights are given in elevation above sea level.

Volume is given in units cubed. You can select which units to use.

For each tool, an accuracy estimate is given. Accuracy depends on a comparison between Nearmap elevation data and LIDAR data.

See How Volume Estimation Works for more information on these parameters.

# Estimating the Volume of a Pit

- Click the
**Volume**tool from the Nearmap toolbar. The**Pit**tab is selected. - Click
**Define Area**. A polygon appears on the map. - Adjust the polygon to match the boundary of the pit. The closer your polygon matches the boundary of the pit, the more accurate the estimate will be.
- Select your preferred units from one of the measurement unit dropdown boxes. The units will be updated to reflect your selection.

The Pit volume estimation tool highlights the deepest areas in the darkest shade of blue.

# Estimate the Volume of a Mound

- Click the
**Volume**tool from the Nearmap toolbar. - Click the
**Mound**tab. - Click
**Define Area**. A polygon appears on the map. - Adjust the polygon to match the boundary of the mound. The closer your polygon matches the boundary of the mound, the more accurate the estimate will be.
- Select your preferred units from one of the measurement unit dropdown boxes. The units will be updated to reflect your selection.

The Mound volume estimation tool highlights the highest areas in the darkest shade of red.

# Estimating the Volume of a Proposed Excavation

- Click the
**Volume**tool from the Nearmap toolbar. - Click the
**Excavation**tab. - Click
**Define Area**. A polygon appears on the map. - Adjust the polygon to match the boundary of your excavation site. The closer your polygon matches the boundary of the excavation site, the more accurate the estimate will be.
- Select your preferred units from one of the measurement unit dropdown boxes. The units will be updated to reflect your selection.
- Specify the
**excavation depth**. This figure will be subtracted from the elevation of the lowest vertex of the polygon to determine the elevation of the bottom of the excavation. The lowest vertex of the polygon is displayed at**Measured from lowest point at**.

The estimated volume of the excavation is displayed at **Volume**.

# How Volume Estimation Works

All three volume estimation tools use Nearmap elevation data to calculate volume. Nearmap elevation data is extrapolated from our imagery. Volume estimation calculations generate a virtual surface, and then work out volumes above and below that surface.

## Creating the Virtual Surface

A virtual surface is generated when the user defines a polygon for a pit, mound or excavation site.

Each vertex on the polygon forms one vertex of the virtual surface. The height of each vertex on the virtual surface is the elevation at that point.

The surface may or may not be planar.

The virtual surface is the best-fit surface for the vertices you define, like a soap bubble. This means it is smooth, and ignores any irregularities in the terrain.

## Generating a Virtual Surface from an Actual Surface

- The Nearmap user selects a site.
- The Nearmap user draws a polygon.
- The MapBrowser calculates the elevation at each vertex of the polygon, and a virtual surface is "stretched" between each elevated vertex.

## Calculating Pit Volume

The pit volume is the volume below the virtual surface and above the actual surface.

## Calculating Mound Volume

The mound volume is the volume above the virtual surface and below the actual surface.

## Calculating Excavation Volume

The excavation volume is:

The volume under the virtual surface, to a specified excavation depth

Plus the volume of mounds above the virtual surface

Minus the volume of pits below the virtual surface

The excavation depth is a user-specified number of metres below the lowest vertex on the polygon that forms the boundary for the virtual surface.

# Limitations and Accuracy

Nearmap elevation data is a Digital Surface Model (DSM). It includes all surface features, such as buildings and vegetation. Nearmap does not have a Digital Terrain Model (DTM). As such, volume calculations in urban areas are likely to be inaccurate.

## Error

Nearmap elevation data is not as accurate as LIDAR data, but it can be sufficient for approximate estimations to support high-level assessments or preliminary planning.

Each volume estimation is accompanied by an estimated error to help you to assess the volume estimation's applicability. This error is based on a comparison with an existing high-quality LIDAR survey.

In general, the error will be significantly higher in built-up urban areas.

## Data Availability

Some older surveys will not have elevation data available. In these cases, you will see a "No data" error message.