AMREL: Automatic Mountain Road Extraction from LiDAR data

AMREL is a software tool to automatically extract roads from large LiDAR data sets of mountainous areas. The road extraction is performed in two steps:

• seeds production using LiDAR derived digital terrain model (DTM) tiles,
• road detection using LiDAR raw data (ground 3D points).

Authors: Philippe Even and Phuc Ngo, LORIA/ADAGIo, Université de Lorraine.

Reference : Even, P. and Ngo, P., 2021. Automatic forest road extraction from LiDAR data of mountainous areas. In International Joint Conference of Discrete Geometry Mathematical Morphology, Uppsala, Sweden, May 24-17, 2021 (Springer LNCS 12708), pp. 93-106. hal-03144147.

QUICK SETUP / COMPILATION GUIDE

• Requires libpng and OpenMP libraries.
• CMakeLists.txt provided for cmake.
• AMREL.pro provided for qmake.

This software has Unix-style command line control. A multi-platform version based on configuration file is available from AMRELmp GitHub repository.

INPUTS

NVM files

NVM is the internal format to encode digital terrain models. It can be produced from standard ASC files using the following command:

AMREL --dtmdir path --import tile.asc --import next1.asc** ... **--import nextn.asc -t mytile

where path is the path to ASC files, tile.asc the suffixed name of the selected ASC file, nextn.asc the name of its nth 8-neighbour tile (optionally used to ensure normal continuity between adjacent tiles) and mytile the unsuffixed name given to the internal format tile. These files should be placed in nvm directory.

TIL files

TIL is the internal format to encode arranged sets of 3D points. It can be produced from XYZ files (a text format where each lines contains X, Y then Z point coordinates separated by a space, that can be extracted from LiDAR raw data using las2txt LAStools command) using the following command:

AMREL --xyzdir path --import tile.txt -t mytile

where path is the path to XYZ files, tile.txt the suffixed name of the selected XYZ file, and mytile the unsuffixed name given to the internal format tile (should be the same than corresponding NVM file). These files should be placed in appropriate til subdirectory.

Point cloud access modes

• Mode "Top" : fast access but heavy memory consumption,
• Mode "Mid" : medium time and memory performance,
• Mode "Eco" : longer execution time but less memory required.

No difference in accuracy between these modes.

Default mode is "Top". Other modes can be selected using --mid or --eco options when running AMREL. Conversions are automatic.

Example of NVM and TIL files

Gris-Mouton sector tiles of Fossard LiDAR data set are available in AMRELtest GitHub repository:

1. Copy the files from AMRELtest/Data/nvm/ directory into $AMREL/nvm/ directory.

2. Copy the files from AMRELtest/Data/til/eco/ directory into AMREL/til/eco/ directory.

3. Copy the file $AMRELtest/Data/tilesets/grismouton.txt into AMREL/tilesets directory.

4. Run AMREL grismouton

The result map is available in AMREL/steps/roads.png image. To test the precision of the achieved detection:

1. Copy this image in AMRELtest/Data/detections/roads_grismouton.png

2. In AMRELtest/Code/ directory, run roadgt --comp grismouton

TYPICAL USES

To extract roads on tname single tile:

AMREL --tile tname

To add tile tname1 and tname2 to tile set tilesets/tsetname.txt:

AMREL --tile tname1 --tile tname2 tsetname

To extract roads on tile set tilesets/tsetname.txt

AMREL tsetname

To only run first stage (slope shading) and output a result map in steps/shade.png:

AMREL --shade --map tsetname

To only run second stage (RORPO filter to enhance elongated shapes) and output a result map in steps/shade.png (assuming the result of previous stage is available) :

AMREL --rorpo --map tsetname

To only run third stage (gradient map computation using 5x5 mask Sobel filter) and output a result map in steps/sobel.png (assuming the result of previous stage is available) :

AMREL --sobel --map tsetname

To only run fourth stage (straight segment extraction using FBSD detector) and output a result map in steps/fbsd.png (assuming the result of previous stage is available) :

AMREL --fbsd --map tsetname

To only run fifth stage (seeds positionning on extracted segments) and output a result map in steps/seeds.png (assuming the result of previous stage is available) :

AMREL --seeds --map tsetname

To only run sixth stage (road extraction using ASD) using extracted seeds (steps/roads.png output map is systematically produced) :

AMREL --asd tsetname

To build seeds from scratch on tiles listed in file tilesets/tsetname.txt using groups of 5x5 tiles:

AMREL --sawing --pad 5 tsetname

To extract roads form selected seeds on tiles listed in file tilesets/tsetname.txt using groups of 7x7 tiles:

AMREL --asd --buf 7 tsetname

OUTPUTS

###Map of extracted roads: roads.png

A PNG format image displaying the extracted roads. It is stored into steps directory.

###Seeds to edit extracted roads in ILSD tool: autodet.txt

Extracted roads can be edited using ILSD, an interactive road extraction tool from raw LiDAR data:

1. Run ILSD

2. In Files menu, select Load settings item, then AMREL/steps/autodet.ini file; this file contains the used road extraction parameters.

3. In Selection menu, select Load selection item, then AMREL/steps/autodet.txt file; this file contains the coordinates of successful seeds which produce the output roads.

LIST OF COMMAND LINE ARGUMENTS

Argument	Description
"tsetname"	Specifies the tile set to process
--tile "name" (or -t "name")	Specifies a tile to add to the tile set
--dtmdir "name"	Specifies the path to imported DTM files
--xyzdir "name"	Specifies the path to imported point files
--import "name" (or -i "name")	Specifies the suffixed name of an imported file
--auto (or "")	Runs seeds selection from DTM map and road detection from point cloud
--shade	Runs only first stage: slope-shading of DTM map
--rorpo	Runs only second stage: RORPO filtering from shaded map
--sobel	Runs only third stage: SOBEL gradient map production from filtered map
--fbsd	Runs only fourth stage: FBSD straight segment detection from gradient map
--seeds	Runs only fifth stage: seeds selection from straight segments
--asd	Runs only sixth stage: road extraction from selected seeds
--sawing	Runs the five first stages: seeds selection from a DTM map
--eco	Uses slow access mode to ground points
--mid	Uses medium access mode to ground points
--pad "size"	Uses size x size groups of tiles for seed selection (positive odd integer value)
--buf "size"	Uses size x size groups of tiles for road extraction (positive odd integer value)
--hill	Outputs hill-shaded DTM in steps/hill.png
--map	Outputs results in a PNG image
--color	Outputs results in a colored PNG image (for each segment, seed or road section)
--dtm	Outputs results superimposed DTM map
--unconnected	Does not interpolate between valid road profiles
--bsminlength "length"	Sets minimal length for straight segment extraction (positive integer value)
--bsmaxthick "thickness"	Sets maximal thickness for straight segment extraction (positive integer value)
--seedshift "shift"	Sets the distance between successive seeds
--seedwidth "width"	Sets seed width
--silent	Suppresses message printing