QEP 339: Processing Algorithm to Convert ASCII Point Cloud Files

QEP-339-pointcloud-text-processing.md

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+# QGIS Enhancement: Add a Processing Algorithm to Convert ASCII Point Cloud Files
+
+**Date** 2025/04/30
+
+**Author** Jean Felder (@ptitjano)
+
+**Contact** jean dot felder at oslandia dot com
+
+**Version** QGIS 3.44
+
+# Summary
+
+Add a new Processing algorithm to QGIS that converts ASCII point cloud files (with custom headers or delimiters) into a format compatible with QGIS point cloud support.
+This enhancement improves flexibility for users by allowing them to prepare these files for visualization and analysis within QGIS.
+
+## Current Limitations
+
+`PDAL` is capable of reading ASCII point cloud files via its `readers.text` driver, which allows specification of custom separators, headers, and column mappings. However QGIS does not expose these options at the moment.
+
+Instead, when importing point clouds, QGIS delegates to `untwine` for generating a COPC file, bypassing `readers.text` options entirely. Since `untwine` cannot interpret these custom options (e.g., separator or header definitions), users are limited to using only files with default formatting.
+
+A previous prototype attempted to work around this by creating a temporary ASCII file and feeding it to `untwine`, but this was not a reliable approach (see [PR #61498](https://github.com/qgis/QGIS/pull/61498)).
+
+Based on the PR feedback, we propose to introduce a dedicated processing to prepare text-based point cloud files *before* QGIS attempts to read them.
+
+## Proposed Solution
+
+The proposed solution is divided into two stages:
+
+1. **Add a new command to `pdal_wrench` named `text_conversion`**
+   This new command will have the following options:
+   - **separator**: Specify the input delimiter (comma, semicolon, tab, space, etc.)
+   - **header**: Define which columns correspond to X, Y, Z, intensity, classification, etc.
+   - **skip**: Number of lines to ignore at the beginning of the file. [Default: 0]
+   - **output**: Output a new ASCII file with default formatting readable by QGIS (using the default `readers.text` configuration)
+
+2. **Add a new Processing algorithm to QGIS**
+   This algorithm will allow to:
+   - Select the input file
+   - Configure parsing options
+   - Invoke `pdal_wrench` in the background to perform the conversion
+   - Generate the formatted file ready for direct use in QGIS
+
+
+## Deliverables
+
+- A new command in [pdal_wrench](https://github.com/PDAL/wrench): `text_conversion`
+- A new QGIS Processing algorithm: `Convert ASCII Point Cloud File`
+
+### Affected Files
+
+- `src/analysis/processing/pdal/qgsalgorithmpdaltextconversion.cpp`
+- `src/analysis/processing/pdal/qgsalgorithmpdaltextconversion.h`
+
+## Risks
+
+Very low. This is a new feature with no changes to existing workflows.
+
+## Performance Implications
+
+N/A
+
+## Backwards Compatibility
+
+N/A
+
+## Issue Tracking ID(s)
+
+- https://github.com/qgis/QGIS/issues/53285