Calibrates distances of landmarks — calibrate • pliman

Calibrating the actual size is possible if any interlandmark distance on the image is known. calibrate() can be used to determine the size of a known distance (cm) on the graph. I invite users to photograph the object together with a scale (e.g., ruler, micrometer...).

Usage

calibrate(img, viewer = get_pliman_viewer())

Arguments

img: An Image object
viewer: The viewer option. If not provided, the value is retrieved using get_pliman_viewer(). This option controls the type of viewer to use for interactive plotting. The available options are "base" and "mapview". If set to "base", the base R graphics system is used for interactive plotting. If set to "mapview", the mapview package is used. To set this argument globally for all functions in the package, you can use the set_pliman_viewer() function. For example, you can run set_pliman_viewer("mapview") to set the viewer option to "mapview" for all functions.

Value

A numeric (double) scalar value indicating the scale (in pixels per unit of known distance).

References

Claude, J. (2008) Morphometrics with R, Use R! series, Springer 316 pp.

Examples

if(isTRUE(interactive())){
library(pliman)
#### compute scale (dots per unit of known distance) ####
# only works in an interactive section
# objects_300dpi.jpg has a known resolution of 300 dpi
img <- image_pliman("objects_300dpi.jpg")
# Larger square: 10 x 10 cm
# 1) Run the function calibrate()
# 2) Use the left mouse button to create a line in the larger square
# 3) Declare a known distance (10 cm)
# 4) See the computed scale (pixels per cm)
calibrate(img)

# scale ~118
# 118 * 2.54 ~300 DPI
}