Application: mm2ply

Overview

mm2ply is a command-line tool that exports the layers of a MOLA metric map (*.mm) file as PLY point cloud files. It converts metric map files into the widely-supported PLY format, making it easy to visualize and process point cloud data in various 3D viewers and processing tools.

Features

  • Exports all point cloud layers from a metric map file

  • Selectively exports specific fields in a custom order

  • Supports both ASCII and binary PLY formats

  • Preserves all point fields (coordinates, colors, intensities, etc.)

  • Automatic field name mapping for standard color attributes

  • Generic field handling for custom point cloud attributes

Usage

mm2ply -i <input.mm> [-o <output_prefix>] [-b] [--export-fields <field1,field2,...>]

Arguments

  • -i, --input <file.mm> (required): Input metric map file

  • -o, --output <prefix> (optional): Prefix for output PLY files. If not specified, uses the input filename without extension

  • -b, --binary (optional): Export in binary format instead of ASCII (default: ASCII)

  • --export-fields <field1,field2,...> (optional): Comma-separated list of fields to export in the specified order. If not provided, all available fields will be exported. Spaces around commas are allowed

Examples

Export a metric map to ASCII PLY files:

mm2ply -i mymap.mm

Export with a custom output prefix:

mm2ply -i mymap.mm -o processed/map

Export in binary format for smaller file sizes:

mm2ply -i mymap.mm -b

Export only specific fields in a custom order:

mm2ply -i mymap.mm --export-fields "x,y,z,intensity"

Export selected fields in binary format:

mm2ply -i mymap.mm -b --export-fields "x, y, z, color_r, color_g, color_b"

Export only 2D coordinates and intensity:

mm2ply -i mymap.mm --export-fields "x,y,intensity"

Combine with custom output prefix:

mm2ply -i mymap.mm -o results/filtered --export-fields "x,y,z,ring,time"

Output

The tool creates separate PLY files for each point cloud layer in the metric map. Files are named using the pattern:

<prefix>_<layer_name>.ply

For example, if your map contains layers named “raw” and “filtered”, you’ll get:

  • mymap_raw.ply

  • mymap_filtered.ply

Field Selection

When using the --export-fields option:

  • Fields must be specified as a comma-separated list

  • Spaces around commas are allowed (e.g., "x, y, z" or "x,y,z")

  • Fields will be exported in the exact order specified

  • All specified fields must exist in the point cloud, or an error will be raised

  • The tool validates field availability and reports available fields if a requested field is not found

  • Color fields (color_r, color_g, color_b) are automatically mapped to PLY standard names (red, green, blue) in the output file, even when using field selection

Supported Point Fields

The tool automatically exports all point attributes, including:

  • Coordinates: x, y, z (float)

  • Colors: Automatically maps color_r/color_rf → red, color_g/color_gf → green, color_b/color_bf → blue

  • Custom float fields: Exported as float properties (e.g., intensity, normals, curvature)

  • Custom double fields: Exported as double properties (e.g., time, timestamps) (MRPT ≥ 2.15.3)

  • Custom uint16 fields: Exported as ushort properties (e.g., ring, color channels) (MRPT ≥ 2.15.3)

  • Custom uint8 fields: Exported as uchar properties (MRPT ≥ 2.15.3)

The specific fields exported depend on the point cloud type in each layer. Use --export-fields to select only the fields you need.

PLY Format Details

The PLY format written by this tool follows the standard specification:

  • ASCII format: Human-readable text with space-separated values

  • Binary format: Compact binary encoding (little-endian) for reduced file size

  • Header: Describes vertex count and property types

  • Data: One vertex per line (ASCII) or record (binary)

Color field name mapping ensures compatibility with standard PLY viewers and processing tools.