Matlab Point Cloud File Io Agent Skill

Point Cloud File I/O

Read and write 3-D point cloud data in MATLAB using Lidar Toolbox file I/O functions, covering PLY, PCD, LAS/LAZ, sensor PCAP, E57, and IDC (Ibeo) formats.

When to Use

• Loading a point cloud file from disk into a pointCloud object
• Saving a pointCloud object to disk in any supported format
• Deciding which reader or writer function to use for a given file format
• Reading LAS/LAZ files with selective filtering (ROI, classification, GPS time)
• Extracting or preserving lidar point attributes (classification, GPS timestamps, scan angle)
• Reading Velodyne, Ouster, or Hesai PCAP sensor recordings frame-by-frame
• Reading multi-scan E57 files with indexed access
• Reading Ibeo IDC sensor recordings with message-based access
• Converting between point cloud formats (e.g., LAS to PLY, PCD to LAZ)

When NOT to Use

• Streaming live sensor data in real time (use velodynelidar, ousterlidar, sicklidar)
• Processing or filtering point clouds after reading (use pcdownsample, pcdenoise)
• Reading or writing surface meshes (use readSurfaceMesh, writeSurfaceMesh)
• Saving point cloud variables to MAT-files (use save)
• Visualizing point clouds (use pcshow, pcplayer, pcviewer)

Must-Follow Rules

• Route by file extension, not by habit — pcread ONLY supports .ply and .pcd files. For .las/.laz use lasFileReader + readPointCloud. For .pcap use the sensor-specific file reader (velodyneFileReader, ousterFileReader, or hesaiFileReader). For .e57 use e57FileReader. Calling pcread on a LAS or PCAP file produces an error, not a warning. Similarly, pcwrite ONLY writes PLY and PCD — for LAS/LAZ output use lasFileWriter + writePointCloud.

• PCAP file readers require a mandatory device identifier — never guess it — velodyneFileReader requires a DeviceModel string (e.g., "HDL32E"). hesaiFileReader requires a DeviceModel string (e.g., "PandarXT32"). ousterFileReader requires a CalibrationFile path (JSON). If the user has not specified the device model or calibration file, ASK — do not assume a default. There is no default value; omitting it causes an error.

• Use two-output syntax to get point attributes from LAS/LAZ — [ptCloud, ptAttributes] = readPointCloud(reader) returns a lidarPointAttributes object containing Classification, GPSTimeStamp, LaserReturn, NumReturns, ScanAngle, and more. The single-output form discards these attributes permanently. Intensity is on the pointCloud object (.Intensity property), NOT on lidarPointAttributes.

• Preserve attributes with three-argument writePointCloud — writePointCloud(writer, ptCloud, ptAttributes) preserves Classification, GPSTimeStamp, and other lidar attributes in LAS/LAZ output. The two-argument form writePointCloud(writer, ptCloud) discards all attributes. If the user has attributes from lasFileReader/readPointCloud, always pass them through.

• PLY only supports ascii and binary encoding — Calling pcwrite(ptCloud, "file.ply", Encoding="compressed") throws an error. Only "ascii" and "binary" are valid for PLY. The "compressed" encoding is exclusive to PCD format. Defaults (R2026a+): PLY="binary", PCD="compressed".

• Always use string syntax — Use double-quoted strings ("text") for all literal text arguments (filenames, device models, encoding values, Name=Value values). Use Name=Value syntax for all name-value pairs. Never use character vectors ('text') or legacy 'Name','Value' pair syntax.

Preflight Procedure

• List MATLAB functions to call
• Check references/INDEX.md for each (function-level + task-level tables)
• Read required quick-ref files
• State at response top: Preflight: quick-ref/xxx.md, quick-ref/yyy.md (or Preflight: none required)

Key Functions

| Function | Purpose | Format | Key Constraint |

|---|---|---|---|

| pcread | Read point cloud from file | PLY, PCD | Single call, returns pointCloud |

| pcwrite | Write point cloud to file | PLY, PCD | Encoding varies by format |

| lasFileReader | Create LAS/LAZ reader object | LAS, LAZ | Two-step: create reader, then readPointCloud |

| lasFileWriter | Create LAS/LAZ writer object | LAS, LAZ | Two-step: create writer, then writePointCloud |

| velodyneFileReader | Create Velodyne PCAP reader | PCAP | Mandatory DeviceModel (2nd arg) |

| ousterFileReader | Create Ouster PCAP reader | PCAP | Mandatory CalibrationFile (2nd arg) |

| hesaiFileReader | Create Hesai PCAP reader | PCAP | Mandatory DeviceModel (2nd arg) |

| e57FileReader | Create E57 reader object | E57 | Use readPointCloud(reader, idx) for multi-scan |

| ibeoLidarReader | Create Ibeo IDC reader object | IDC | Use readMessages to read scan data |

Decision Framework

READING — What is the file extension?
├── .ply / .pcd → pcread(filename)
├── .las / .laz → lasFileReader(filename) + readPointCloud(reader)
├── .pcap (Velodyne) → velodyneFileReader(filename, deviceModel)
├── .pcap (Ouster)  → ousterFileReader(filename, calibrationFile)
├── .pcap (Hesai)   → hesaiFileReader(filename, deviceModel)
├── .e57           → e57FileReader(filename) + readPointCloud(reader, idx)
└── .idc (Ibeo)    → ibeoLidarReader(filename) + readMessages(reader)

WRITING — What output format does the user need?
├── .ply → pcwrite(ptCloud, "file.ply")
│         Encoding: "ascii" or "binary" (default: binary)
├── .pcd → pcwrite(ptCloud, "file.pcd")
│         Encoding: "ascii", "binary", or "compressed" (default: compressed)
├── .las → lasFileWriter("file.las") + writePointCloud(writer, ptCloud)
└── .laz → lasFileWriter("file.laz") + writePointCloud(writer, ptCloud)
           Optional: pass ptAttributes as 3rd arg to preserve attributes

PCAP sensor identification: If the user says "Velodyne", "Ouster", or "Hesai" — use the matching reader. If they just say "PCAP file" without specifying the sensor, ASK which sensor produced it.

Ibeo IDC files: If the user has an .idc file, use ibeoLidarReader. Unlike other readers, it uses readMessages (not readPointCloud or readFrame) and returns message-based scan data.

Velodyne device models: VLP16, PuckLITE, PuckHiRes, VLP32C, HDL32E, HDL64E, VLS128, VelarrayH800

Hesai device models: Pandar128E3X, Pandar64, PandarQT, PandarXT32

Gotchas

pcread called on LAS/LAZ file

pcread only supports PLY and PCD formats. Attempting to use it on LAS, LAZ, PCAP, or E57 files throws an error.

% WRONG: pcread does not support LAS
ptCloud = pcread("survey.las");

% CORRECT: Use lasFileReader for LAS/LAZ
reader = lasFileReader("survey.las");
ptCloud = readPointCloud(reader);

Compressed encoding on PLY file

The "compressed" encoding is only valid for PCD format. PLY supports only "ascii" and "binary".

% WRONG: compressed not supported for PLY
pcwrite(ptCloud, "output.ply", Encoding="compressed");

% CORRECT: use binary for compact PLY
pcwrite(ptCloud, "output.ply", Encoding="binary");

% CORRECT: compressed is valid for PCD
pcwrite(ptCloud, "output.pcd", Encoding="compressed");

Using pcwrite for LAS/LAZ output

pcwrite does not support LAS or LAZ format. It only handles PLY and PCD.

% WRONG: pcwrite cannot write LAS
pcwrite(ptCloud, "output.las");

% CORRECT: use lasFileWriter for LAS/LAZ
writer = lasFileWriter("output.las");
writePointCloud(writer, ptCloud);

Losing attributes with two-argument writePointCloud

When writing LAS/LAZ, the two-argument form discards lidar point attributes. Always pass the attributes object if available.

% WRONG: attributes are discarded
reader = lasFileReader("input.laz");
[ptCloud, ptAttr] = readPointCloud(reader);
writer = lasFileWriter("output.laz");
writePointCloud(writer, ptCloud);  % ptAttr lost!

% CORRECT: preserve attributes with 3-argument form
reader = lasFileReader("input.laz");
[ptCloud, ptAttr] = readPointCloud(reader);
writer = lasFileWriter("output.laz");
writePointCloud(writer, ptCloud, ptAttr);

Accessing classification from the wrong object

Classification, GPSTimeStamp, LaserReturn, and other lidar-specific attributes are on lidarPointAttributes, not on pointCloud. The pointCloud object holds Intensity (and Location, Color, Normal).

% WRONG: pointCloud does not have Classification
reader = lasFileReader("data.laz");
ptCloud = readPointCloud(reader);
labels = ptCloud.Classification;  % Error

% CORRECT: Use two-output syntax
reader = lasFileReader("data.laz");
[ptCloud, ptAttributes] = readPointCloud(reader);
labels = ptAttributes.Classification;
intensity = ptCloud.Intensity;  % Intensity is on pointCloud

Reading all PCAP frames without a loop

PCAP readers are frame-based iterators. There is no single function to load all frames at once.

% WRONG: No readAll or similar function
reader = velodyneFileReader("lidarData_ConstructionRoad.pcap", "HDL32E");
allPoints = readPointCloud(reader);  % readPointCloud is not a method

% CORRECT: Loop with hasFrame/readFrame
reader = velodyneFileReader("lidarData_ConstructionRoad.pcap", "HDL32E");
while hasFrame(reader)
    ptCloud = readFrame(reader);
end

Patterns

Read a PLY or PCD file

ptCloud = pcread("scene.ply");
fprintf("Points: %d\n", ptCloud.Count);
fprintf("X range: [%.2f, %.2f]\n", ptCloud.XLimits);

Read LAS file with classification filtering

reader = lasFileReader("aerial.laz");
[ptCloud, ptAttributes] = readPointCloud(reader, Classification=[2 6]);
labels = ptAttributes.Classification;
fprintf("Ground + building points: %d\n", ptCloud.Count);

Read Velodyne PCAP frames

reader = velodyneFileReader("lidarData_ConstructionRoad.pcap", "HDL32E");
fprintf("Total frames: %d\n", reader.NumberOfFrames);
while hasFrame(reader)
    ptCloud = readFrame(reader);
end

Read E57 file with multiple scans

reader = e57FileReader("building.e57");
fprintf("Scans in file: %d\n", reader.NumPointClouds);
for idx = 1:reader.NumPointClouds
    ptCloud = readPointCloud(reader, idx);
    fprintf("Scan %d: %d points\n", idx, ptCloud.Count);
end

Write point cloud to PLY (binary)

ptCloud = pointCloud(rand(1000,3), Color=uint8(rand(1000,3)*255));
pcwrite(ptCloud, fullfile(tempdir, "output.ply"), Encoding="binary");

Write point cloud to PCD (compressed)

ptCloud = pcread(fullfile(toolboxdir("lidar"), "lidardata", "highwayScene.pcd"));
pcwrite(ptCloud, fullfile(tempdir, "scene_compressed.pcd"), Encoding="compressed");

Read LAS and write to LAZ preserving attributes

reader = lasFileReader("input.las");
[ptCloud, ptAttr] = readPointCloud(reader);
writer = lasFileWriter(fullfile(tempdir, "output.laz"));
writePointCloud(writer, ptCloud, ptAttr);

Convert PCD to PLY

ptCloud = pcread("scene.pcd");
pcwrite(ptCloud, fullfile(tempdir, "scene.ply"), Encoding="binary");

Convert LAS to PCD

reader = lasFileReader("survey.las");
ptCloud = readPointCloud(reader);
pcwrite(ptCloud, fullfile(tempdir, "survey.pcd"), Encoding="compressed");

Read Ibeo IDC file

reader = ibeoLidarReader("sensor_data.idc");
fprintf("Message types: %s\n", strjoin(reader.MessageTypes, ", "));
fprintf("Total messages: %d\n", reader.NumMessages);

% Read all messages — returns array of pointCloud objects
ptClouds = readMessages(reader);

% Two-output form: get message metadata (timestamps, labels, plane info)
[ptClouds, messageData] = readMessages(reader);

% Filter by message type: "Scan" or "PointCloudPlane"
ptClouds = readMessages(reader, Messages="Scan");

% Filter by time range
tStart = reader.FileInfo.TimeStamps{1}(1);
tEnd = tStart + seconds(10);
ptClouds = readMessages(reader, Time=[tStart tEnd]);

ibeoLidarReader key details:

• Supports IDC files from Ibeo FUSION SYSTEM/ECU sensors
• Two message types: "Scan" (data type 0x2205) and "PointCloudPlane" (data type 0x7510)
• readMessages returns an array of pointCloud objects (one per message)
• Second output messageData is a cell array of structs with MessageType, TimeStamp, and (for PointCloudPlane) Label, ReferencePoint, PlaneOrientation
• FileInfo property is a table with columns: MessageType, DataType, Description, NumMessages, TimeStamps
• All properties are read-only

Conventions

• Use tempdir for output paths in examples and tests to avoid permission issues
• Default to Encoding="binary" for PLY and omit encoding for PCD (default compressed is best)
• Always use double-quoted strings ("text") and Name=Value syntax — never character vectors or 'Name','Value' pairs
• Include file extension explicitly in filename — format is determined from extension
• PLY flattens organized M-by-N-by-3 to unorganized M-by-3; use PCD to preserve organized structure
• NaN/Inf values are skipped when writing to PLY
• lasFileWriter only supports unorganized pointCloud objects

References

| Load when... | Reference |

|---|---|

| Reading or writing LAS/LAZ files, need filtering NV-pairs, attribute details, or writer properties | references/quick-ref/las-io.md |

| Reading PCAP files from Velodyne, Ouster, or Hesai sensors | references/quick-ref/pcap-readers.md |

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