Plot Displacement Vectors

Creates a visualization of the displacement vectors from source (distorted) to target (true) coordinates for a set of homologous points.

Usage

plot_displacement(
  gcp_data,
  title = "Distortion Displacement Vectors",
  subtitle = "Arrows point from distorted to true locations",
  arrow_color = "darkred",
  point_color = "red"
)

Arguments

gcp_data

An sf object of homologous points, typically the output of read_gcps(). Must contain source_x, source_y, target_x, and target_y columns.

title

A character string for the plot's main title.

subtitle

A character string for the plot's subtitle.

arrow_color

A character string specifying the color of the displacement arrows.

point_color

A character string specifying the color of the points marking the source locations.

Value

A ggplot object, which can be further customized using standard ggplot2 syntax.

Details

This function is a key exploratory tool for understanding the nature and magnitude of positional error in a dataset before correction. It plots arrows that originate at the distorted source coordinates and point to the correct target coordinates. This provides an immediate visual sense of the spatial patterns in the distortion (e.g., rotation, scaling, or non-linear warping).

Examples

# --- 1. First, create a demo dataset to work with ---
demo_files <- create_demo_data(type = "complex")
#>    -> Homologous points saved to: /tmp/RtmpaCHjm6/demo_gcps.csv
#>    -> Distorted map saved to: /tmp/RtmpaCHjm6/demo_map.shp
gcp_data <- read_gcps(gcp_path = demo_files$gcp_path, crs = 3857)

# --- 2. Create the default displacement plot ---
plot_displacement(gcp_data)


# --- 3. Customize the plot with different titles and colors ---
plot_displacement(
  gcp_data,
  title = "My Custom Displacement Plot",
  subtitle = "Visualizing error vectors",
  arrow_color = "blue",
  point_color = "orange"
)