# cartographer/configuration_files/trajectory_builder.lua

## Overview

Shared configuration for trajectory builders (both 2D and 3D). Contains common parameters used by both `TrajectoryBuilder2D` and `TrajectoryBuilder3D`.

## Configuration

```lua
TRAJECTORY_BUILDER = {
  pure_localization = false,
  pure_localization_trimmer = {
    max_submaps_to_keep = 3,
  },
}
```

## Parameters

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `pure_localization` | bool | `false` | Enable pure localization mode (no mapping) |
| `pure_localization_trimmer.max_submaps_to_keep` | int | `3` | Submaps to retain in pure localization |

## Pure Localization Mode

When `pure_localization = true`:
- No new submaps are created
- Existing map is used for localization only
- `PureLocalizationTrimmer` keeps only recent submaps
- Useful for: repeated runs in known map, multi-session localization

## Usage

```lua
-- In your robot config
include "trajectory_builder_2d.lua"

TRAJECTORY_BUILDER = {
  pure_localization = true,
  pure_localization_trimmer = {
    max_submaps_to_keep = 5,
  },
}

TRAJECTORY_BUILDER_2D = {
  -- Override 2D params for localization
  ceres_scan_matcher = {
    occupied_space_weight = 20.,
    translation_weight = 100.,
    rotation_weight = 400.,
  },
}
```

## See Also

- [trajectory_builder_2d.lua](trajectory_builder_2d.md) — 2D-specific config
- [trajectory_builder_3d.lua](trajectory_builder_3d.md) — 3D-specific config
- [Submap2D](../mapping/2d/submap_2d.md) — Submap lifecycle and trimming