simulateData {rPACI}

Simulate data as measured by a Placido disk corneal topographer

Description

The function simulateData permits to simulate a wide variety of datasets that appear in clinical practice, as a result of measuring an individual eye with a Placido disk corneal topographer (see vignette("topographersDataFormat", package = "rPACI")).

Usage

simulateData(
  rings = 15,
  pointsPerRing = 256,
  diameter = 12,
  ringRadiiPerturbation = 0,
  maximumMireDisplacement = 0,
  mireDisplacementAngle = 0,
  mireDisplacementPerturbation = 0,
  ellipticAxesRatio = 1,
  ellipticRotation = 0,
  overallNoise = 0,
  seed = 0
)

Arguments

rings

The total number of rings of mires in the sample (typically in the range 18-30, around 24).

pointsPerRing

The number of points to be sampled in each ring (typically 256 or 360).

diameter

Diameter of the simulated dataset (in mm, typically around 8-12 mm).

ringRadiiPerturbation

Stochastical perturbation of the mires radii distribution (typically between 0 (no perturbation) and 1 (high perturbation)).

maximumMireDisplacement

Mires displacement, drift or off-centering (expressed in mm, and should be a reasonable number according to the diameter used.

mireDisplacementAngle

Direction of mires drift (an angle in degrees, typically in the range 0-360 with 0 meaning positive x direction).

mireDisplacementPerturbation

Stochastical perturbation of the mires drift (typically between 0 (no perturbation) and 1 (high perturbation)).

ellipticAxesRatio

Rate or quotient between the major and minor axes of each ellipse (related to the ellipse eccentricity; 1 means a perfect circle (no eccentricity)).

ellipticRotation

Direction or orientation of the ellipses (an angle in degrees, typically in the range 0-360 with 0 meaning positive x direction).

overallNoise

Random, white noise of a certain magnitude in the Cartesian coordinates of the sampled points (relative to the diameter and the number of rings; 0 means no noise, and 1 large noise).

seed

A seed, included for repeatability when using random perturbations.

Details

This function produces a dataset in the same format as the one read by readCSO from a file, i.e., a list with three columns (x and y coordinates of each point and its ring index) and a row per data point, according to the function parameters (by default, 6144 rows or data points).

See vignette("simulating", package = "rPACI") for additional details. The examples included there show different ways of using simulateData, by adding different transformations or perturbations to the basic circular pattern. Some of the obtained patterns can correlate with certain clinical conditions, such as keratoconus, comma, or others.

The simulated dataset can be later used according to the package workflow explained in the vignette("packageUsage", package = "rPACI").

Value

A data.frame with columns:

x		The X Cartesian coordinates of sampled points
y		The Y Cartesian coordinates of sampled points
ring index		Number or index of the ring from which each point is sampled

The resulting data.frame also includes in its Parameters attribute (attr(result,'Parameters')) the list of parameters used for the simulation.

Examples

# Simulating with default parameters
dataset = simulateData()  
plot(dataset$x,dataset$y)

# Simulating with 20 rings and a diameter of 8 mm
dataset = simulateData(rings = 20, diameter = 8)
plot(dataset$x,dataset$y)

# Simulating with default parameters and 500 points per ring (15x500 points)
dataset = simulateData(pointsPerRing = 500)
plot(dataset$x,dataset$y)

# Simulating an elliptic dataset, with ellipses axis ratio of 0.8 and an orientation of 45 degrees.
dataset = simulateData(ellipticAxesRatio = 0.8, ellipticRotation = 45)
plot(dataset$x,dataset$y)

# To see the parameters used in the simulation, access the 'Parameters' attribute:
attr(dataset,'Parameters')