The goal of quad is to provide a framework for fleshing out raster-origin mesh geometry when needed.
You can install the development version of quad from GitHub with:
# install.packages("devtools")
devtools::install_github("hypertidy/quad")This is a basic example which shows you how to expand out the grid when you really need to.
What is a grid? A raster is a six-number specification, dimension and extent.
Let’s say we have set of raster data, a matrix in R with ncols, nrows and an extent.
library(quad)
(dm <- dim(elev)[2:1])
#> [1] 360 180
ib <- quad_index(dm)
vb <- quad_vert(dm)
str(ib)
#> int [1:259200] 362 361 0 1 723 722 361 362 1084 1083 ...
str(vb)
#> num [1:130682] 0 1 0.00278 1 0.00556 ...That is the basis for building a partly expanded quadmesh, and it is fast.
##previous we might have used anglr
system.time(anglr::as.mesh3d(elev))
#> user system elapsed
#> 0.040 0.012 0.051
## what if it was much bigger
el <- elev[seq(1, nrow(elev), length.out = 3600), seq(1, ncol(elev), length.out = 1800)]
system.time(m3d <- anglr::as.mesh3d(el))
#> user system elapsed
#> 6.706 1.940 8.645
str(m3d)
#> List of 6
#> $ vb : num [1:4, 1:6485401] 0 0 -3522 1 1 ...
#> $ material :List of 1
#> ..$ color: chr [1:6480000] "#F8D074" "#F8D074" "#F8D074" "#F8D074" ...
#> $ normals : NULL
#> $ texcoords: NULL
#> $ meshColor: chr "faces"
#> $ ib : int [1:4, 1:6480000] 1 2 3603 3602 2 3 3604 3603 3 4 ...
#> - attr(*, "class")= chr [1:2] "mesh3d" "shape3d"
## when we use {quad} we have access to the intermediate steps
system.time({
vb <- quad_vert(c(3600, 1800))
vb <- rbind(matrix(vb, nrow = 2), z = 0.0, h = 1.0)
vb[,1] <- scales::rescale(vb[,1], c(-180, 180))
vb[,2] <- scales::rescale(vb[,2], c(-90, 90))
ib <- matrix(quad_index(c(3600, 1800), ydown = TRUE), nrow = 4L)
## ok still WIP but you see where we're going, anglr needed a
## RasterLayer *object* just to get that extent scaling (!!!), when
## we don't even need an array (it's just dim+extent)
## this is faster and it scales to generic workflows
})
#> user system elapsed
#> 0.535 0.433 0.968
str(vb)
#> num [1:4, 1:6485401] -180 180 -180 180 -90 ...
#> - attr(*, "dimnames")=List of 2
#> ..$ : chr [1:4] "" "" "z" "h"
#> ..$ : NULL
str(ib)
#> int [1:4, 1:6480000] 3602 3601 0 1 7203 7202 3601 3602 10804 10803 ...- Mercury
- ensure alignment of anglr and quad and control with ydown and comparison to rgl is sane and easy
- provide flat, matrix, dataframe versions of each output (and compare with {geometries})
- bridge to {textures} and other packages that are for specific outputs (mesh3d, and various 3D formats, and just plotting with vectorized grid.polygon)
Please note that the quad project is released with a Contributor Code of Conduct. By contributing to this project, you agree to abide by its terms.
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