Getting height measurements from imagery

Height measurements can be obtained when a sensor model exists. Sun angle information is required to make measurements using shadows.

Tip:

The units for these measurements can be changed in the Mensuration Results window.

Measuring a structure's height

The Base To Top Height tool calculates the height of a feature by measuring from the base of the feature to the top of the feature. Measurements are assumed to be perpendicular to the base; therefore, the building is not tapered or built at an angle. The line being measured along the building must have its top endpoint vertically above the base start point.

In the example below, there are many points along each of these buildings where you can easily identify the base of the building and the location directly on the top.

1. Click the layer in the Image Analysis window.
2. Activate the Base To Top Height tool.
3. Click a point at the base of the structure.
4. Click the corresponding point at the top of the structure.

Measuring a structure's height from the shadow only

The Base To Shadow Height tool calculates the height of a structure by measuring from the base of the structure to the top of the structure's shadow. The point in the shadow must represent a point on the structure that is perpendicular to the base.

When Measure in 3D is checked, it will use the DEM to refine the calculation. The elevation layer as well as the image layer must be selected in the Image Analysis window in order for the Measure in 3D check box to be enabled.

In this example, the image has been enhanced to make the shadow more visible. Using the Base To Shadow Height tool, you can find the height of this lamppost by measuring from the base of the lamp to the top of the lamp's shadow. This is a better tool to use than the Base To Top Height tool because it would be difficult to pick the top of the lamp in this scenario.

1. Click the layer in the Image Analysis window.
2. Activate the Base To Shadow Height tool.
3. Click a point at the bottom of the structure.
4. Click the corresponding point at the top of the structure's shadow.

Measuring a structure's height from the structure and shadow

The Top To Shadow Height tool calculates the height of a structure by measuring from the top of the structure to the top of the structure's shadow. The points on the structure and its shadow must represent the same point.

When Measure in 3D is checked, it will use the DEM to refine the calculation.

In the example below, the point where the shadow intersects with the building (bottom of the shadow) is blocked by a tree; therefore, it should not be used. The correct way to identify the height of this building is to identify a point on the top of the building that can be identified in the top of the shadow, such as the one identified by the blue arrow.

You may also use this tool if you need to measure the height of a part of the structure or the height of a structure that is not a rectangle. For example, below, the height of this pointed roof can only be measured from the top of the roof point to the top of the shadow, because there is no way to easily pick the base point, which would be directly below the roof's peak.

This tool is also useful for obtaining the height of an object on the top of a structure. For example, if there is a utility room you want to measure on the roof of the building, you can identify the top point of this feature in the image, and then identify the same point in the shadow.