segm_watershed {OTBsegm} | R Documentation |
Watershed segmentation
Description
Applies the watershed segmentation algorithm to an image file or a SpatRaster
Usage
segm_watershed(
image,
otb,
thresh = 0.01,
level = 0.1,
mode = "vector",
vector_neighbor = FALSE,
vector_stitch = TRUE,
vector_minsize = 1L,
vector_simplify = 0.1,
vector_tilesize = 1024L,
mask = NULL
)
Arguments
image |
path or |
otb |
output of |
thresh |
depth threshold units in percentage of the maximum depth in the image |
level |
flood level for generating the merge tree from the initial segmentation (from 0 to 1) |
mode |
processing mode, either 'vector' or 'raster'. See details |
vector_neighbor |
logical. If FALSE (the default) a 4-neighborhood connectivity is activated. If TRUE, a 8-neighborhood connectivity is used |
vector_stitch |
logical. If TRUE (the default), scans polygons on each side of tiles and stitch polygons which connect by more than one pixel |
vector_minsize |
integer. Objects whose size in pixels is below the minimum object size will be ignored during vectorization |
vector_simplify |
simplify polygons according to a given tolerance (in pixel). This option allows reducing the size of the output file or database. |
vector_tilesize |
integer. User defined tiles size for tile-based segmentation. Optimal tile size is selected according to available RAM if NULL |
mask |
an optional raster used for masking the segmentation. Only pixels whose mask is strictly positive will be segmented |
Details
The watershed segmentation algorithm is a region-based image segmentation technique inspired by topography. It treats the grayscale intensity of an image as a topographic surface, where brighter pixels represent peaks and darker pixels represent valleys. The algorithm simulates flooding of this surface to separate distinct regions. Steps:
Topographic Interpretation: The input image is treated as a 3D landscape, where pixel intensity corresponds to elevation.
Flooding Process: Starting from local minima, the algorithm simulates water flooding the surface. As the water rises, distinct regions (basins) are formed.
Watershed Lines: When two basins meet, a boundary (watershed line) is formed to prevent merging.
Region Labeling: Each basin is assigned a unique label, producing a segmented image where boundaries are clearly defined.
The processing mode 'vector' will output a vector file, and process the input image piecewise. This allows performing segmentation of very large images. IN contrast, 'raster' mode will output a labeled raster, and it cannot handle large data. If mode is 'raster', all the 'vector_*' arguments are ignored.
Value
sf
or SpatRaster
Examples
## Not run:
## load packages
library(link2GI)
library(OTBsegm)
library(terra)
## load sample image
image_sr <- rast(system.file("raster/pnoa.tiff", package = "OTBsegm"))
## connect to OTB (change to your directory)
otblink <- link2GI::linkOTB(searchLocation = "C:/OTB/")
## apply segmentation
results_ms_sf <- segm_watershed(
image = image_sr,
otb = otblink,
thresh = .1,
level = .2
)
## End(Not run)