# fsMapViewSetAltitudeReference<no value>
This function can be used to select which point of reference will be used to compute altitude. This function is only valid when the `fsMapViewSetViewMode` is set to "Altitude" view mode.

 

 

##### Syntax

``` wasm
bool fsMapViewSetAltitudeReference(
    FsContext ctx,
    FsTextureId id,
    FsMapViewAltitudeReference eRef
    )
```

 

##### Members

{{< table-wrapper >}}

| Parameters | Description                                                                                             |
|------------|---------------------------------------------------------------------------------------------------------|
| `ctx`      | A value of type `FsContext` provided as an argument of the gauge callback.                              |
| `id`       | The MapView render ID as returned by the function `fsMapViewCreate`.                                    |
| `eRef`     | Set the altitude reference to be used for the MapView. See the [Remarks](#remarks) for possible values. |

{{< /table-wrapper >}}


 

##### Return Values

Returns false

-   if no texture matches the given MapView ID
-   the `ctx` is invalid
-   the given `eRef` is invalid

Otherwise it will return true.

 

 

##### Remarks

The table below shows the available references for the MapView altitude:

{{< table-wrapper >}}

| eModes                                 | Description                                                                                                          |
|----------------------------------------|----------------------------------------------------------------------------------------------------------------------|
| `FS_MAP_VIEW_ALTITUDE_REFERENCE_GEOID` | Altitude colours will be applied with reference to the height from the Geoid ({{< glossterm >}}msl{{< /glossterm >}}) |
| `FS_MAP_VIEW_ALTITUDE_REFERENCE_PLANE` | Altitude colours will be applied with reference to the current aircraft altitude.                                    |

{{< /table-wrapper >}}


{{< image-center
    src="images/6_Programming/WASM/map_view_3_reference.png"
    alt="Example Of The Difference Between Aircraft And Geoid Reference" >}}