Available with 3D Analyst license.
Measuring 3D straight-line distances between points of interest allows you to perform operations such as finding the shortest distance between two points. This could be the shortest distance between a point on the surface and a 3D feature such as a window on a building. Also, this can be used to find the shortest distance between two points of interest floating independently of the surface, for example, the distance between two windows in separate buildings.
To measure the straight-line distance in 3D, you can use the Measure Direct 3D Line tool 
on the Measure dialog box. Measuring straight-line distances in 3D can be thought of as measuring about a pivotal point using a rope.
- Click the Measure tool
on the Tools toolbar.
- Click the Measure Direct 3D Line tool .
- Click the location where you want to start measuring the 3D distance.
- Move the pointer to the point of interest and click to start measuring the 3D distance. If you want to continue measuring a straight 3D line, simply move the pointer to another location and click to add vertices.
- Double-click where you want to end the line.
- Optionally, while measuring, if you want to navigate around to view the measurement from a different perspective, you can press the ESC key once. This freezes the measurement graphic. You can then press the ALT key to navigate in the scene.
The 3D distance between the last two points of interest, along with the total 3D distance from the starting point, is displayed in the Measure window.