When using grid_canopy(), the output is dependend on the subcircle tweak used in p2r(). This makes sense, since after "expanding" each point to a disk, the extent of the point cloud is larger - it can be argued that it makes sense, that the user gets as chm the full extent of the "extended" point cloud - although having a larger output extent than input extent may still be surprising to some.
However the algorithm breaks when using a reference raster to determine alignment/resolution, and I think that shouldn't happen (I'd rather get the "cropped" chm). Here is a code example, if it isn't reproducible on your data I can send you some:
# create reference raster ref_raster <- raster(extent(tile_dtm), res = 1) crs(ref_raster) = crs(tile_dtm) # make sure the las cloud extent is the same as the reference raster tile_las = clip_roi(tile_las, extent(ref_raster))
Calling the following causes the error:
> r_chm_bottom = grid_canopy(tile_las, res=ref_raster, p2r(0.5)) Fehler in C_rasterize(las, layout, subcircle, 1L) : C++ unexpected internal error in 'rasterize': point out of raster.
Here we see, what the algorithm would like to output, without being restricted by an extent:
> r_chm = grid_canopy(tile_las, res=1, p2r(0.5)) > extent(r_chm_bottom) class : Extent xmin : 2692999 xmax : 2694001 ymin : 1124999 ymax : 1126001
When using grid_metrics or setting p2r(subcircle = 0) , which is the default, it works without complaints. A side question: Is grid_metrics(~max(Z)) basically equivalent to grid_canopy(p2r())?
> r_npoints_all = grid_metrics(tile_las, ~max(Z), res=ref_raster) > extent(r_npoints_all) class : Extent xmin : 2693000 xmax : 2694000 ymin : 1125000 ymax : 1126000
Also the pitfree algorithm apparently has a crop back to the original extent implemented, as grid_canopy(pitfree(subcircle > 0)) also works fine:
> r_chm = grid_canopy(tile_las, res=ref_raster, pitfree(thresholds = c(0, 2, 5, 10, 15), max_edge = c(0, 1), subcircle = 0.5) ) > extent(r_chm_bottom) class : Extent xmin : 2693000 xmax : 2694000 ymin : 1125000 ymax : 1126000
I suggest having a p2r optional parameter cropToInputExtent = TRUE (you may have a more concise name for it ;] ), that allows for extension by the subcircle tweak, but defaults to extent(input) = extent(output) [as generally may be expected and allows for usage of a reference raster grid_canopy(las, res=raster(extent(las), res=1), p2r(0.5)) ].
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