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# Measurements using Reference Surfaces

This page describes the concept and how to measure using different Reference Surfaces.

More information related to mobile mapping measurements on Orbit Desktop and Orbit WebClient, see :

- Desktop : 3D Measurements
- WebClient : Measure Sidebar

## DEM Intersection

### Principle of Reference Planes Intersection

A 3D coordinate measured via DEM intersection is the result of the intersection of the reconstructed 3D line through focal point of the camera and measured point in the image and DEM.

### How to measure

DEM Intersection can only be used in an Image View and DEM has to be part of the Run\Project. Open one image and measure a point with one click.

## Reference Planes Intersection

### Principle of Reference Planes Intersection

Result of the measurement with **Reference Planes Intersection** measuring technique is a 3D coordinate derived by intersection of the 3D line (photo position - point measured in the photo) with horizontal or vertical plane. If **Show hover** is enabled in preferences 3D hover will indicate found planes.

- Horizontal plane can be assumed to be ground plane as it is calculated from the photo position 3D coordinates and camera height defined in the project. Used in Mobile Mapping context, not relevant for UAS and Oblique types of data.
- Vertical planes require a 2D/3D line or area vector layer opened. Plane used in measurement is a vertical plane which closest to the measured position line\outline of the area belongs to.

### How to measure

**Horizontal plane**

Open one image and measure a point on the ground with one click. If measurement does not look correct please check that camera height is set correctly in the Orbit Mapping Run.

**Vertical plane**

Add a vector line or area vector layer to datasets list. Open one image and measure a point in a vertical plane.

## Ground Surface Intersection

Result of the measurement with **Ground Surface Intersection** measuring technique is a 3D coordinate derived by intersection of the 3D line (photo position - point measured in the photo) with the horizontal ground surface plane. The ground surface is calculated from the photo position 3D coordinates and camera height defined in the project. Used in Mobile Mapping context, not relevant for UAS and Oblique types of data.

### How to measure

Open one image and measure a point on the ground with one click. If measurement does not look correct please check that camera height is set correctly in the Orbit Mapping Run.