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Get started

Source: vignettes/rasterpic.qmd

Getting started with rasterpic is straightforward: you need an image file (png, jpeg/jpg or tiff/tif) and a supported spatial input class, such as an object from the sf, terra or stars packages.

Basic usage

This example geotags an image using the shape of Austria:

library(sf)
library(terra)
library(rasterpic)

# Load plotting packages.
library(tidyterra)
library(ggplot2)

# Set the spatial object and image.
x <- read_sf(system.file("gpkg/austria.gpkg", package = "rasterpic"))
img <- system.file("img/vertical.png", package = "rasterpic")

# Geotag the image.
default <- rasterpic_img(x, img)

autoplot(default) +
  geom_sf(data = x)
Figure 1: Image geotagged with the coordinates of Austria.

Options

rasterpic_img() provides options for expansion, alignment, cropping and masking.

Expand

The expand argument expands the raster extent beyond the spatial object:

expand <- rasterpic_img(x, img, expand = 1)

autoplot(expand) +
  geom_sf(data = x)
Figure 2: Example image expansion.

Alignment

The halign and valign arguments control the alignment of the image within the spatial extent:

bottom <- rasterpic_img(x, img, valign = 0)

autoplot(bottom) +
  geom_sf(data = x)
Figure 3: Example image alignment.

Crop and mask

The crop, mask and inverse arguments control whether the raster is cropped to the object extent and masked to the object shape:

mask <- rasterpic_img(x, img, crop = TRUE, mask = TRUE)

autoplot(mask)

maskinverse <- rasterpic_img(x, img, crop = TRUE, mask = TRUE, inverse = TRUE)

autoplot(maskinverse)
Figure 4: Example masked image.
Figure 5: Example inverse masked image.

Supported spatial input classes

rasterpic_img() supports the following spatial input classes:

  • sf classes: sf, sfc, sfg and bbox.
  • terra classes: SpatRaster, SpatVector and SpatExtent.
  • stars class: stars.
  • A numeric coordinate vector of the form c(xmin, ymin, xmax, ymax).

rasterpic_img() is an S3 generic. Methods for extent-like inputs use the object extent, and vector methods can also mask the image to the object shape.

Supported image formats

rasterpic can read the following image formats:

  • png files.
  • jpeg/jpg files.
  • tiff/tif files.