Perform measurements

ArcGIS Drone2Map provides tools to identify points and measure the area of polygons, the length of features, and the volume of objects in images. All measurements are calculated in 3D, which uses the digital surface model (DSM) as the default. Alternatively, you can use the digital terrain model (DTM) for the calculation of 3D measurements. You can change the default units of measurement in the Mensuration Results window before or after performing measurements.

Note:

Keep the following in mind when measuring:

• The quality of the measurement results depends on the quality of the ground control points used when processing the images. See the Manage Control topic for best practices using ground control in your projects.
• Measurements are calculated using the DSM. To activate the mensuration tools, process a DSM and add it to the map.

Make a measurement

The subsections below provide workflows for measuring a point, distance, area, or volume of features in images.

Identify a point

The Point tool identifies the location of a point.

To identify a point feature, complete the following steps:

1. On the Analysis tab, in the Measure gallery, click the Point tool.
2. Click a point on the image.

Measure distance

The Distance tool measures the distance between two or more points.

To measure distance or length of features on a map, complete the following steps:

1. On the Analysis tab, in the Measure gallery, click the Distance tool.
2. Click two or more points along the feature you're measuring.
3. Double-click the last point to stop measuring.

Measure an area

The Area tool calculates the surface area and perimeter of a feature.

To measure an area on the map, complete the following steps:

1. On the Analysis tab, in the Measure gallery, click the Area tool.
2. Click three or more points along the feature you're measuring.
3. Double-click the last point to stop measuring.

Volume

The volume of features can be measured from any georeferenced raster dataset, mosaic dataset, or image service composed of an elevation surface such as a DSM or DTM. Draw a polygon around the feature to calculate and display cut and fill volumes on the map, in the Results pane, and in the mensuration report.

You can measure the volume of objects in a DSM or DTM using the Volume tool . If you have a choice of elevation surface types for an area of interest, it is recommended that you use a DSM, which best represents the elevation of features above the ground.

Base surface

The volume measurement is calculated from a reference surface determined by the polygon delineating the object you want to measure. The reference surface—called the base surface—can be created using any of the following Base Surface options:

• Constant—A user defined value that defines a flat base surface

• Interpolate—Uses the z-value at each vertex in your sketch to interpolate a base surface for the volume calculation.

• Minimum—Uses the minimum z-value found in the sketch vertices to define a flat base surface at the minimum elevation.

• Maximum—Uses the maximum z-value found in the sketch vertices to define a flat base surface at the maximum elevation

• Mean—Uses the mean z-value from the sketch vertices to define a flat base surface at the mean elevation.

Cut and fill volumes are calculated from the difference between the digitized feature and the defined base surface. Ground features below the base surface result in fill values, and above ground features result in cut values. The total volume measurement is cut value + fill value.

Note:

The raster layer used as a backdrop for digitizing features of interest can be a multispectral image, a thematic image, an elevation surface, or other type of supported raster dataset. The only requirement is that features and objects digitized in the layer must be represented in the elevation dataset to obtain accurate volume measurements. This is because the volume measurement is calculated using the elevation surface dataset defined in the Mensuration Options pane.

Collect a volume measurement

To collect a volume measurement of a feature in an image, complete the following steps:

1. On the Analysis tab, in the Measure gallery, click the Volume tool.
2. Digitize a polygon around the feature of interest by clicking vertices and double-clicking to close the polygon.

   This polygon is used to define the base surface and the object for volumetric measurement.

Copy a measurement

Measurements can be copied and used to measure either the DSM and DTM at the same location by modifying mensuration settings.

To copy and measure on another elevation surface, complete the following steps:

1. In the Mensuration Results pane, click the mensuration options button .
2. In the Elevation section, choose the elevation surface to be used for mensuration.

   The DSM and DTM must be processed in the project before both choices will appear.

3. Click OK.
4. Select the measurement from the Mensuration Results pane.
5. Click the copy measurement button .

   The selected feature is copied and measured to the newly defined elevation surface.

Export measurements

Point, line and polygon measurement features can be exported for use in other projects. This allows the measurement of the same area across different times. Measurements that are exported maintain their original measurement value fields.

To export a measurement, complete the following steps:

1. On the Analysis tab, in the Measure group, click the Export button .
2. If exporting to a file geodatabase, click the browse button and browse to and choose an existing geodatabase, or click the Create file geodatabase button to create a new file geodatabase.

   To add the measurements to a feature dataset, check the Output to Feature Dataset check box and provide a name.

3. If exporting as a shapefile, use the browse button to define the output location.
4. Check the layers that you want to export in the Measurements to Export section.
5. Click Export to export the measurements.

Import measurements

Point, line, and polygon measurement features can be imported from feature classes or shapefiles. This allows the measurement of the same area across different times. Measurements that are imported maintain their original measurement value fields.

To import a measurement, complete the following steps:

1. On the Analysis tab, in the Measure group, click the Import button.
2. Click the Browse button to open the Browse to Feature Class window.
3. Browse to the measurement feature class, feature dataset, or shapefile and select it.
4. Click Open to add the selection to the Import Measurements window.
5. Check the layers that you want to import in the Detected Measurement Types section.
6. Click Import to import the measurements.

Mensuration Results pane

The results from each measurement are listed in the Mensuration Results pane. To open the pane, on the Analysis tab, in the Measure group, click Results. The following properties are included for each measurement:

• Type—The type of measurement can be point, distance, area, or volume.
• Name—Defaults are sequential for each type of measurement.
• Description—You can add a text description for each measurement.
• Sensor Name—This shows the name of the camera maker for the specific drone.
• Sensor Model—This shows the specific model of sensor the drone used.
• Time of measurement—The time of the volume measurement is defined as month/day/year h:mm:ss AM/PM.

Each type of measurement includes the following unique information about the respective type when selected in the Mensuration Results pane:

• Point—The x,y coordinates of the point measurement
• 3D Point—The x,y,z coordinates of the point measurement
• Distance—The total distance of the measurement and the distance of each segment in multisegment measurements
  • Sun Azimuth—Sun azimuth angle measured in decimal degrees clockwise from north
  • Sun Angle Elevation (3D Distance)—Angular height of the sun above the horizon in decimal degrees
• Area
  • Area—2D surface area of the polygon, in the units selected, such as square meters
  • Perimeter—Linear measurement of the polygon, in the units selected, such as meters
• Volume
  • Volume—Calculated as cut + fill, in the units selected, such as cubic meters
  • Cut—Cut volume of above base surface features, in the units selected, such as cubic meters
  • Fill—Fill volume of below base surface features, in the units selected, such as cubic meters
  • Area—2D surface area of the polygon, in the units selected, such as square meters
  • Perimeter—Linear measurement of the polygon, in the units selected, such as meters

Note:

If you make volume measurements in Drone2Map, the error of the calculation is also reported. The error is calculated as follows:

• Cut Volume error = <number of cut cells> * 1.5 * Ground Sample Distance³

• Fill Volume error = <number of fill cells> * 1.5 * GSD³

• Total Volume error = Cut Volume error + Fill Volume error

Mensuration options

To choose the units for each measurement type , click the Mensuration Options button in the upper right corner of the Mensuration Results pane. Additionally, you can edit symbols and colors for the measurement types.

The Level of Precision value determines the number of decimal places for the specified units; the default value is four decimal places. Select a value between 1–12.

If you create both a DSM and a DTM, you can set the Elevation surface dataset to calculate the volume measurement.

The Base Surface option allows you to specify a method for determining the base surface reference. Click the drop-down arrow to select from the following options:

• Constant—A user-defined value that defines a flat base surface is used.
• Interpolate—The z-value at each vertex in a sketch is used to interpolate a base surface for the volume calculation.
• Minimum—The minimum z-value from the sketch vertices is used to define a flat base surface at the minimum elevation.
• Maximum—The maximum z-value from the sketch vertices is used to define a flat base surface at the maximum elevation.
• Mean—The mean z-value from the sketch vertices is used to define a flat base surface at the mean elevation.

Save the measurements

The measurement types are saved in the project's geodatabase as the appropriate feature classes. For example, point measurements are saved as a point feature class, distance measurements are saved as a polyline feature class, and area and volume measurements are saved as a polygon feature class. The location and feature class type is handled in the project file, so there is no need to locate or manage these files.

Measurements are saved when you save or exit the project. When the project file is loaded, the saved measurements are also loaded and available for viewing or editing in the Mensuration Results pane. The measurements are linked with the attribute table of the feature class to the appropriate source file.

Note:

Changing the default location of the project's geodatabase file may cause existing measurements to disappear from the Mensuration Results pane.

Mensuration report

You can generate and save a report listing the measurements. Click the Generate Report button in the Mensuration Results pane, and name and save the report. All selected measurements in the Mensuration Results pane are written to a text file. If no results are selected, all measurements for the map are written to the report.

The following information is recorded for each measurement:

• Measurement name—The name of the measurement in the map
• Type of measurement—The identification of the measurement as a point, distance, area, or volume measurement
• Measurement result—The results of the measurement in the map, in the units specified
• Description—The description you added to the measurement data
• Time of measurement—The time the measurement was collected