NAME
i.cutlines - Creates semantically meaningful tile borders
KEYWORDS
imagery,
tiling
SYNOPSIS
i.cutlines
i.cutlines --help
i.cutlines input=name output=name number_lines=integer edge_detection=string [existing_cutlines=name[,name,...]] no_edge_friction=integer lane_border_multiplier=integer [min_tile_size=integer] [zc_threshold=float] [zc_width=integer] [canny_low_threshold=float] [canny_high_threshold=float] [canny_sigma=float] [tile_width=integer] [tile_height=integer] [overlap=integer] processes=integer memory=integer [--overwrite] [--help] [--verbose] [--quiet] [--ui]
Flags:
- --overwrite
- Allow output files to overwrite existing files
- --help
- Print usage summary
- --verbose
- Verbose module output
- --quiet
- Quiet module output
- --ui
- Force launching GUI dialog
Parameters:
- input=name [required]
- Raster map to use as input for tiling
- output=name [required]
- Name of output vector map with cutline polygons
- number_lines=integer [required]
- Number of tile border lines in each direction
- edge_detection=string [required]
- Edge detection algorithm to use
- Options: zc, canny
- Default: zc
- existing_cutlines=name[,name,...]
- Input vector maps with existing cutlines
- Or data source(s) for direct OGR access
- no_edge_friction=integer [required]
- Additional friction for non-edge pixels
- Default: 5
- lane_border_multiplier=integer [required]
- Multiplier for borders of lanes compared to non-edge pixels
- Default: 10
- min_tile_size=integer
- Minimum size of tiles in map units
- zc_threshold=float
- Sensitivity of Gaussian filter (i.zc)
- Default: 1
- zc_width=integer
- x-y extent of the Gaussian filter (i.zc)
- Default: 9
- canny_low_threshold=float
- Low treshold for edges (i.edge)
- Default: 3
- canny_high_threshold=float
- High treshold for edges (i.edge)
- Default: 10
- canny_sigma=float
- Kernel radius (i.edge)
- Default: 2
- tile_width=integer
- Width of tiles for tiled edge detection (pixels)
- tile_height=integer
- Height of tiles for tiled edge detection (pixels)
- overlap=integer
- Overlap between tiles for tiled edge detection (pixels)
- Default: 1
- processes=integer [required]
- Number of parallel processes
- Default: 1
- memory=integer [required]
- RAM memory available (in MB)
- Default: 300
i.cutlines tiles the images into tiles with irregular borders that
avoid cutting through meaningful objects. This allows tiling an image for
parallel processing while avoiding border effects.
The approach used in i.cutlines is inspired by Soares et al (2016).
The module first uses an edge detection algorithm (which the user can chose
with the edge_detection parameter) to identify edges in the image. It
then uses r.cost
and r.drain to
draw lines through the image, following edges when possible and going straight
when there are none.
The user can determine the number of lines desired (number_lines) in each
direction and the friction associated with pixels which are not on an edge
detected in the image (no_edge_friction). The higher this value, the
more the module will follow the detected edges.
In order to avoid that all lines gather into one single lowest cost path, the
module defines a lane for each desired line. The parameter
lane_border_multiplier defines the a multiplier of the
no_edge_friction value, in order to define the cost to
cross that line, i.e. the lower the value, the more likely cutlines will join
each other across lanes. Output is in the form of vector polygon tiles. The user
can decide a minimum size defined in map units (min_tile_size). Tiles
smaller than that size will be merged with the neighboring tile they share the
longest border with.
The user can provide a series of auxiliary vector maps which contain existing
cutlines (roads, boundaries, etc) that the module should take into account
(existing_cutlines). These can be either lines or polygons. The module
will transform all to potential cutlines.
For edge detection the user can chose between the i.zc
module or the i.edge addon. For the former, the user
can determine the zc_threshold and the zc_width parameters. For
the latter, the canny_low_threshold, canny_high_threshold and
canny_sigma parameters. See the manual page of the respective modules
for details about these parameters which might need tuning to fit to the
specific image. As these modules read the entire image into RAM,
i.cutlines allows the user to run split the image into rectangular
tiles and to process each tile separately. Tiles can be defined with the
tile_width, tile_height and overlap parameters. If
processes is higher than one, these tiles will be processed in parallel
as will the r.cost calls for the two directions.
The memory parameter determines the memory used both for the
r.cost runs.
Until GRASS GIS version 7.4 included, there was a parameter name conflict between
i.zc and the
GridModule class in pygrass. For older GRASS GIS versions tiled edge
detection is thus only possible with
i.edge.
Using the default
i.zc
edge detection without tiling,
default parameters and 10 horizontal and 10 vertical cutlines, creating
vector polygon output:
# ortho photo subarea
g.region raster=ortho_2001_t792_1m n=221070 s=219730 -p
i.cutlines input=ortho_2001_t792_1m number_lines=10 output=ortho_tiles_zc
![](i_cutlines_default.png)
Irregular vector tiles created for the NC demo data set orthophoto (default setting)
Using the
i.edge
Canny edge detection with tiling and (needed) tile overlap, increased memory,
two parallel processes and 10 horizontal and 10 vertical cutlines, creating
vector polygon output:
# ortho photo subarea
g.region raster=ortho_2001_t792_1m n=221070 s=219730 -p
i.cutlines input=ortho_2001_t792_1m number_lines=10 edge_detection=canny \
tile_width=500 tile_height=500 overlap=10 memory=2000 processes=2 output=ortho_tiles_canny
![](i_cutlines_canny.png)
Irregular vector tiles created for the NC demo data set orthophoto (Canny edge detection)
Soares, Anderson Reis, Thales Sehn Körting, and Leila Maria Garcia Fonseca. 2016.
"Improvements of the Divide and Segment Method for Parallel Image Segmentation."
Revista Brasileira de Cartografia 68 (6),
http://www.lsie.unb.br/rbc/index.php/rbc/article/view/1602
i.zc,
i.edge,
r.tile,
v.mkgrid,
i.segment
Moritz Lennert
SOURCE CODE
Available at:
i.cutlines source code
(history)
Latest change: Monday Jan 30 19:52:26 2023 in commit: cac8d9d848299297977d1315b7e90cc3f7698730
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GRASS Development Team,
GRASS GIS 8.4.1dev Reference Manual