orfeo-toolboxqgisqgis-processingraster
I am looking for QGIS function to extract (or detect) edge from a raster, which was referred in here, How to digitize a raster automatically as answer by @MappaGnosis.
The name could have changed since then, or it may have been integrated into other tool… I cannot find it in my QGIS Processing Toolbox (2.14.10 and 2.18.2).
There are similar tools such as GRASS "i.zc Zero-crossing" and SAGA "Gaussian filter", but I am hoping to find this QGIS geoalgorithm.
The Processing menu is tied to the Processing plugin. So please check if you have deactivated the Processing plugin in the Plugin Manager.
There is a couple of things wrong with this:
mat <- matrix(1/25,ncol=5, nrow=5)
raster_res <- focal(raster1, mat, FUN="mean", na.rm=T)
The argument to supply the function is called fun, not FUN. You give each value a weight of 1/25, and then you want to use "mean". However, you should use "sum" in that case! (which is the default, and because you were using FUN instead of fun, that is what happened anyway.) However, since you have missing values and you are using na.rm=TRUE, you really need to give each value a weight of 1 and then use mean.
Also, as you want to fill in missing values, not change existing values, I would use NAonly = TRUE, together with pad=TRUE (to pad virtual rows and columns with NAs outside of the raster).
Here is an example:
library(raster)
# example data
logo <- raster(system.file("external/rlogo.grd", package="raster"))
set.seed(0)
i <- sample(ncell(logo), 200)
logo[i] <- NA
plot(logo)
m <- matrix(1, ncol=5, nrow=5)
r <- focal(logo, m, fun="mean", na.rm=TRUE, NAonly=TRUE, pad=TRUE)
plot(r)
To see for which cells the values were estimated
plot(as(reclassify(is.na(logo), cbind(0, NA)), 'SpatialPolygons'), add=TRUE)
Also, if you want to write the raster to a file, instead of using writeRaster you should do that in one step:
r <- focal(logo, m, fun="mean", na.rm=TRUE, NAonly=TRUE, pad=TRUE, filename="smooth.tif", overwrite=TRUE)
Best Answer
The Edge Extraction tool may have been moved to the Orfeo Toolbox as this focuses on image analysis. The Orfeo Toolbox contains a number of edge extraction tools using various methods such as: