Extract lines from image_contour_detector about image HOT 7 CLOSED

I understand that you want to include this in the package but I would prefer to have then a separate method as in

image_contour_detector <- function(x, Q=2.0, ...){
  UseMethod("image_contour_detector")
}

image_contour_detector.matrix <- function(x, Q, ...){
}

image_contour_detector.RasterLayer <- function(x, Q, ...){
}

image_contour_detector.SpatialGridDataFrame <- function(x, Q, ...){
}

In general there is certainly a looot of overlap possible between computer vision and spatial communities. The first thing on my mind would be a package which easily converts images between these 2 (especially covering things like r/g/b and that the topleft is (0,0) and regular R has bottomleft as (0,0).
This last should probably be in a different package so that it can easily switch between representations of R package magick, opencv, plain base arrays, sp, sf, raster... objects, HCR objects, textline objects andsoforth.

from image.

There is code at https://github.com/bnosac/image/blob/master/image.ContourDetector/R/contour_detector.R#L85:L88 which extracts the lines as an sp object, does that help you further?

from image.

many thanks!
I found it only later...now I'm trying to figure out how to refer them to the original georeferenced data.
What do the output's x and y refer to? I tried adding the minX and minY (lower left corner) but it seems that somewhere in the input process there's a sort of rescaling, in addition to the coords being lost. In this way I get lines with not real sizes and related to a relative reference system...

from image.

x and y correspond to the horizontal and vertical positions of the points defining the contour line
note that the magick R package the point (0,0) starts at the topleft

from image.

good to know!

BTW, I got a bit deeper and adapted your code to accept RasteLayers as well. I don't know if it might be of interest for your package but I think users using the tool on spatial data may appreciate it :) (there's quite a lot of room for your tools in such field)

image_contour_detector <- function(x, Q=2.0) {
if( is(r,"RasterLayer") ){
  
  minX = raster::extent(x)[1]
  minY = raster::extent(x)[3]
  
  resol = raster::res(x)[1]
  
  x = as.matrix(x)
} else { stopifnot(is.matrix(x)) }

if( anyNA(x) ){
  x[is.na(x)] = 0
  warning("NA values found and set to 0")
}

if( min(x, na.rm = TRUE)>=0 & max(x, na.rm = TRUE) <=255 ){ warning("Values range between 0 and 255: Q might be set to 0")}

contourlines <- image.ContourDetector:::detect_contours(x, 
                                X=nrow(x),
                                Y=ncol(x),
                                Q=Q)
names(contourlines) <- c("x", "y", "curvelimits", "curves", "contourpoints")
contourlines$curvelimits <- contourlines$curvelimits+1L
from <- contourlines$curvelimits
to <- c(tail(contourlines$curvelimits, contourlines$curves-1L)-1L, contourlines$contourpoints)
curve <- unlist(mapply(seq_along(from), from, to, FUN=function(contourid, from, to) rep(contourid, to-from+1L), SIMPLIFY = FALSE))
contourlines$data <- data.frame(x = contourlines$y, y = nrow(x) - contourlines$x, curve_id = curve)
contourlines$data$x = contourlines$data$x * resol + minX
contourlines$data$y = contourlines$data$y * resol + minY
contourlines <- contourlines[c("curves", "contourpoints", "data")]
class(contourlines) <- "cld"
contourlines
}

An idea for further enhancement could be to add a "asSpatial" boolen option to get directly the spatial object, but probably that would be too specific for the general purpose..or not?
BTW thanks and keep up the good work!

from image.

unfortunately I can't help with methods, yet, because I didn't get my hands on the topic...but I hope to contribute in the next future!
I think it's really necessary to expand the capabilities of the package towards the other main representations of arrays

from image.

Fixed with merging #24

from image.