README.md

In mdsumner/qwad: Intermediate Forms of Raster Grids

quad

The goal of quad is to provide a framework for fleshing out raster-origin mesh geometry when needed.

Installation

You can install the development version of quad from GitHub with:

# install.packages("devtools")
devtools::install_github("hypertidy/quad")

Example

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 ...

TODO

• [x] 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)

Code of Conduct

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.

mdsumner/qwad documentation built on Jan. 16, 2024, 2:01 a.m.