---
title: Atlantis
---

# Atlantis

```{figure} ../../_static/videos/atari/atlantis.gif
:width: 120px
:name: Atlantis
```

This environment is part of the <a href='..'>Atari environments</a>. Please read that page first for general information.

## Description

Your job is to defend the submerged city of Atlantis. Your enemies slowly descend towards the city and you must destroy them before they reach striking distance. To this end, you control three defense posts.You lose if your enemies manage to destroy all seven of Atlantis' installations. You may rebuild installations after you have fought of a wave of enemies and scored a sufficient number of points.

For a more detailed documentation, see [the AtariAge page](https://atariage.com/manual_html_page.php?SoftwareID=835)

## Actions

Atlantis has the action space `Discrete(4)` with the table below lists the meaning of each action's meanings.
As Atlantis uses a reduced set of actions for `v0`, `v4` and `v5` versions of the environment.
To enable all 18 possible actions that can be performed on an Atari 2600, specify `full_action_space=True` during
initialization or by passing `full_action_space=True` to `gymnasium.make`.

| Value   | Meaning     |
|---------|-------------|
| `0`     | `NOOP`      |
| `1`     | `FIRE`      |
| `2`     | `RIGHTFIRE` |
| `3`     | `LEFTFIRE`  |

## Observations

Atari environment have two possible observation types, the observation space is listed below.
See variants section for the type of observation used by each environment id.

- `obs_type="rgb" -> observation_space=Box(0, 255, (210, 160, 3), np.uint8)`
- `obs_type="ram" -> observation_space=Box(0, 255, (128,), np.uint8)`

Additionally, `obs_type="grayscale"` cause the environment return a grayscale version of the rgb array for observations with the observation space being `Box(0, 255, (210, 160), np.uint8)`
### Rewards

You score points for destroying enemies, keeping installations protected during attack waves. You score more points
if you manage to destroy your enemies with one of the outer defense posts.
For a more detailed documentation, see [the AtariAge page](https://atariage.com/manual_html_page.php?SoftwareID=835).

## Variants

Atlantis has the following variants of the environment id which have the following differences in observation,
the number of frame-skips and the repeat action probability.

| Env-id                       | obs_type=   | frameskip=   | repeat_action_probability=   |
|------------------------------|-------------|--------------|------------------------------|
| Atlantis-v0                  | `"rgb"`     | `(2, 5)`     | `0.25`                       |
| Atlantis-ram-v0              | `"ram"`     | `(2, 5)`     | `0.25`                       |
| Atlantis-ramDeterministic-v0 | `"ram"`     | `4`          | `0.25`                       |
| Atlantis-ramNoFrameskip-v0   | `"ram"`     | `1`          | `0.25`                       |
| AtlantisDeterministic-v0     | `"rgb"`     | `4`          | `0.25`                       |
| AtlantisNoFrameskip-v0       | `"rgb"`     | `1`          | `0.25`                       |
| Atlantis-v4                  | `"rgb"`     | `(2, 5)`     | `0.0`                        |
| Atlantis-ram-v4              | `"ram"`     | `(2, 5)`     | `0.0`                        |
| Atlantis-ramDeterministic-v4 | `"ram"`     | `4`          | `0.0`                        |
| Atlantis-ramNoFrameskip-v4   | `"ram"`     | `1`          | `0.0`                        |
| AtlantisDeterministic-v4     | `"rgb"`     | `4`          | `0.0`                        |
| AtlantisNoFrameskip-v4       | `"rgb"`     | `1`          | `0.0`                        |
| ALE/Atlantis-v5              | `"rgb"`     | `4`          | `0.25`                       |
| ALE/Atlantis-ram-v5          | `"ram"`     | `4`          | `0.25`                       |
| ALE/Atlantis2-v5             | `"rgb"`     | `4`          | `0.25`                       |
| ALE/Atlantis2-ram-v5         | `"ram"`     | `4`          | `0.25`                       |

## Difficulty and modes

It is possible to specify various flavors of the environment via the keyword arguments `difficulty` and `mode`.
A flavor is a combination of a game mode and a difficulty setting. The table below lists the possible difficulty and mode values
along with the default values.

| Available Modes   | Default Mode   | Available Difficulties   | Default Difficulty   |
|-------------------|----------------|--------------------------|----------------------|
| `[0, 1, 2, 3]`    | `0`            | `[0]`                    | `0`                  |

## Version History

A thorough discussion of the intricate differences between the versions and configurations can be found in the general article on Atari environments.

* v5: Stickiness was added back and stochastic frameskipping was removed. The environments are now in the "ALE" namespace.
* v4: Stickiness of actions was removed
* v0: Initial versions release
