# NED or “Compass” vs. ENU or “Math” Angles

For historical and common practice reasons, we use two different coordinate conventions in this manual: North-East-Down (NED) and East-North-Up (ENU).  Sailors and pilots often use a NED coordinate system, while mathematicians and some IMUs use an ENU coordinate system.

The Cerulean ROVL coordinate system is described below and essentially passes the East-North-Up coordinate frame used by the internal IMU through with no transformations. For convenience we sometimes call this the “Math” coordinate frame. In this coordinate frame, the yaw (heading) angle is zero when the vehicle X-axis points due east, and the angle increases as the vehicle rotates counterclockwise (i.e., turns to port).

Sailors prefer a North-East-Down coordinate frame compatible with ordinary compasses, with the heading (yaw) angle zero when the vehicle X-axis points north, and the angle increasing as the vehicle rotates clockwise (turns to starboard).


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.ceruleansonar.com/c/rov-locator/rovl-coordinate-systems-and-angles/ned-or-compass-vs.-enu-or-math-angles.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.