Understanding Raster Plotting in Windows with R Package rasters

Raster plotting is a fundamental aspect of geospatial data analysis, particularly when working with satellite or aerial imagery. The raster package in R provides an efficient way to handle and plot raster objects. However, users have reported encountering errors while trying to plot raster objects on Windows using the latest version of the raster package (2.3-0).

In this article, we will delve into the technical details behind raster plotting in R and explore possible reasons for the issues encountered on Windows.

Background: Raster Data and Package rasters

Raster data represents spatial information as a grid of pixels, where each pixel corresponds to a specific value or attribute. The raster package provides an interface to work with raster objects, allowing users to read, write, manipulate, and visualize them.

The raster package relies on the rgdal package for geospatial data handling, which is a crucial component in R’s geospatial ecosystem. When working with raster data on Windows, it’s essential to understand how these packages interact under the hood.

The Issue: Error with Plotting Raster Object

The error message produced by the raster package when trying to plot a raster object on Windows is:

Error in `colnames<-`(value = "A055E") : 
  length of 'dimnames' [2] not equal to array extent

This error occurs when the package attempts to assign a new name (in this case, “A055E”) to the second dimension of the raster object. However, the length of the dimnames attribute does not match the extent of the raster data.

Understanding Raster Object Structure

A raster object consists of several components:

1. Data: The actual pixel values representing the spatial information.
2. Dimensions: The number of rows and columns in the raster grid, denoted by dimX and dimY, respectively.
3. Extents: The bounding box of the raster data, defined by xmin, xmax, ymin, and ymax.
4. Dimension names: Strings assigned to the first two dimensions (e.g., “A055E” for the second dimension in our example).

Possible Reasons for Error on Windows

When working with raster objects on Windows, there are a few possible reasons why this error might occur:

• Package Conflicts: The raster package (2.3-0) has been updated to fix compatibility issues with other packages, which may lead to conflicts when running on older versions of R or libraries.
• Library Mappings: Windows uses different library mappings than Linux-based systems for geospatial data handling, leading to potential discrepancies in how rgdal and raster interact.

Solution: Update Package rasters

According to the package author, updating the raster package to a newer version (at least 2.3-1) resolves the issue on Windows.

# Install the latest version of the raster package
install.packages("raster", repos = "https://cran.r-project.org")

# Update to the latest version of the raster package
update.packages(checkForConflicts = FALSE)

Additional Recommendations

To ensure seamless raster plotting on Windows, consider implementing additional steps:

• Check Package Dependencies: Verify that all required packages are up-to-date and properly installed before running your analysis.
• Specify R Environment: Use the RHOME environment variable to specify the path to the R installation directory. This ensures consistent results across different environments.

Conclusion

Raster plotting with the raster package in R can be challenging on Windows due to potential compatibility issues and library mappings. However, by updating the raster package and taking additional steps to ensure accurate dependencies and R environment configuration, users can overcome these obstacles and successfully work with raster data.

Code Example

Here’s an example of how to create a simple raster object using the raster package:

# Load necessary packages
library(raster)

# Create a raster object from a sample file
map <- raster("path/to/sample.tif")

# Plot the raster object
plot(map)

This code creates a basic raster object using the provided file path and plots it.

Last modified on 2023-06-01