---
title: Ray casts in Defold
brief: Ray casts are used to read the physics world along a linear ray. This manual explains how this works.
---

## Ray casts

Ray casts are used to read the physics world along a linear ray. To cast a ray into the physics world, you provide a start and end position as well as [a set of collision groups](/manuals/physics-groups) to test against.

If the ray hits a physics object you will get information about the object it hit. Rays intersect with dynamic, kinematic and static objects. They do not interact with triggers.

```lua
function update(self, dt)
  -- request ray cast
  local my_start = vmath.vector3(0, 0, 0)
  local my_end = vmath.vector3(100, 1000, 1000)
  local my_groups = { hash("my_group1"), hash("my_group2") }

  local result = physics.raycast(my_start, my_end, my_groups)
  if result then
      -- act on the hit (see 'ray_cast_response' message for all values)
      print(result.id)
  end
end
```

::: sidenote
Ray casts will ignore collision objects that contain the starting point of the ray. This is a limitation in Box2D.
:::