# indexStart

> The first index from RayTracingGeometryInstanceConfig.indexBuffer that defines this ray tracing geometry instance.

## Definition

* **Type:** Property
* **Namespace:** [UnityEngine.Rendering](/engine/6000.3/script-reference/unityengine/rendering.md)
* **Assembly:** UnityEngine.CoreModule

```csharp
public uint indexStart { readonly get; set; }
```

### Remarks

This value must be a multiple of 3 and together with [RayTracingGeometryInstanceConfig.indexCount](/engine/6000.3/script-reference/unityengine/rendering/raytracinggeometryinstanceconfig/indexcount.md) it must define a valid range into [RayTracingGeometryInstanceConfig.indexBuffer](/engine/6000.3/script-reference/unityengine/rendering/raytracinggeometryinstanceconfig/indexbuffer.md).