R: Evaluate Logical Expression Involving Pixel Images and Return...

solutionset {spatstat.geom} | R Documentation

## Evaluate Logical Expression Involving Pixel Images and Return Region Where Expression is True

### Description

Given a logical expression involving one or more pixel images, find all pixels where the expression is true, and assemble these pixels into a window.

### Usage

      solutionset(..., envir)

### Arguments

`...` | An expression in the R language, involving one or more pixel images.
`envir` | Optional. The environment in which to evaluate the expression.

### Details

Given a logical expression involving one or more pixel images, this function will find all pixels where the expression is true, and assemble these pixels into a spatial window.

Pixel images in `spatstat` are represented by objects of class `"im"` (see `im.object`). These are essentially matrices of pixel values, with extra attributes recording the pixel dimensions, etc.

Suppose `X` is a pixel image. Then `solutionset(abs(X) > 3)` will find all the pixels in `X` for which the pixel value is greater than 3 in absolute value, and return a window containing all these pixels.

If `X` and `Y` are two pixel images, `solutionset(X > Y)` will find all pixels for which the pixel value of `X` is greater than the corresponding pixel value of `Y`, and return a window containing these pixels.

In general, `...` can be any logical expression involving pixel images.

The code first tries to evaluate the expression using `eval.im`. This is successful if the expression involves only (a) the names of pixel images, (b) scalar constants, and (c) functions which are vectorised. There must be at least one pixel image in the expression. The expression `expr` must be vectorised. See the Examples.

If this is unsuccessful, the code then tries to evaluate the expression using pixel arithmetic. This is successful if all the arithmetic operations in the expression are listed in `Math.im`.

### Value

A spatial window (object of class `"owin"`, see `owin.object`).

### Author(s)

Adrian Baddeley Adrian.Baddeley@curtin.edu.au and Rolf Turner r.turner@auckland.ac.nz

### See Also

`im.object`, `owin.object`, `eval.im`, `levelset`

### Examples

      # test images
      X <- as.im(function(x,y) { x^2 - y^2 }, unit.square())
      Y <- as.im(function(x,y) { 3 * x + y  - 1}, unit.square())

      W <- solutionset(abs(X) > 0.1)
      W <- solutionset(X > Y)
      W <- solutionset(X + Y >= 1)

      area(solutionset(X < Y))

      solutionset(distmap(cells) < 0.05)

[Package spatstat.geom version 2.3-2 Index]