Getting height measurements from imagery

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

TipTip:

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

Measuring a structure's height from the structure only

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

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

Using the object only

Steps:
  1. Click the layer in the Image Analysis window.
  2. Click a point at the bottom of the structure.
  3. 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 Base To Shadow Height calculates the height of a structure by measuring from the base of the structure to the top of the structure's shadow on the ground. 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.

In this example, the image has been enhanced to make the shadow more visible. Using this tool, you can find the height of this lamp post by measuring from the base of the lamp to the top of the lamp shadow. This is a better tool to use in this scenario since it would be difficult to pick the top of the lamp.

Measuring the shadow only

Steps:
  1. Click the layer in the Image Analysis window.
  2. Click a point at the bottom of the structure.
  3. 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 Top To Shadow Height calculates the height of a structure by measuring from the top of the structure to the top of the structure's shadow on the ground. 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 cannot 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 shadow, such as the one identified by the blue arrow.

Using Top To Top Shadow

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.

Using Top To Top Shadow

This tool is also useful for obtaining the height of an object on the top of a structure. For example, if there was a smaller room than the dimensions of the building or a tower on the top. You can identify the top point of this feature in the image, then identify the same point in the shadow.

Steps:
  1. Click the layer in the Image Analysis window.
  2. Click a point at the top the structure.
  3. Click the corresponding point at the top of the structure's shadow.

Related Topics

9/10/2014