Скачать или смотреть Solving the Geopandas Coordinate Transformation Dilemma: From EPSG:28992 to EPSG:3857

Discover how to properly convert coordinates using `Geopandas` and understand the intricacies between different spatial reference systems.
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Solving the Geopandas Coordinate Transformation Dilemma: From EPSG:28992 to EPSG:3857

When dealing with geographic information system (GIS) data, one of the most common challenges that developers face is correctly transforming coordinate systems. A particular case involves trying to convert coordinates from EPSG:28992 (the RD new coordinate system used in the Netherlands) to EPSG:3857 (also known as Web Mercator). This blog discusses the common pitfalls in this conversion process, highlights the solution, and clarifies some fundamental concepts of coordinate systems.

The Problem at Hand

As illustrated in the case presented, using Geopandas to transform coordinates can lead to confusion. The data pulled from a shapefile in EPSG:28992 appeared legitimate:

[[See Video to Reveal this Text or Code Snippet]]

This printout showed the geometries in meters, which is expected in a projected coordinate system:

[[See Video to Reveal this Text or Code Snippet]]

However, upon transforming these coordinates to EPSG:3857:

[[See Video to Reveal this Text or Code Snippet]]

The output was puzzling, yielding unexpected values in the geometry column:

[[See Video to Reveal this Text or Code Snippet]]

The immediate assumption might be that something went wrong during the conversion. This assumption is common among newcomers who may expect the output coordinates in degrees instead of meters.

Understanding Coordinate Reference Systems

Before diving into the solution, it's important to recognize how different coordinate reference systems (CRS) work:

EPSG:28992 (RD New): This is a projected coordinate system that uses meters and is specific to the Netherlands.

EPSG:3857 (Web Mercator): This system is also metric but presents coordinates differently on virtual maps, which allows for better manipulation and viewability in web applications.

EPSG:4326 (WGS 84): A widely used geographic coordinate system that outputs coordinates in degrees (latitude and longitude).

Common Confusion

A primary source of confusion arises from the expectation that the output of EPSG:3857 should be in degrees, similar to what you would find in EPSG:4326. In reality, both EPSG:3857 and EPSG:28992 use meters for their calculations. Hence, coordinate transformations do not yield latitude and longitude values but rather vary with respect to the projection utilized:

If you need the data in degrees, you should convert it to EPSG:4326.

The Solution: Correctly Transforming Your Data

When converting from EPSG:28992 to EPSG:3857, it’s crucial to maintain the understanding that both formats use metric measurements. If you're sure that the point you are converting is accurately positioned (e.g., north of Utrecht), there's likely nothing wrong with the transformation itself.

Steps to Correctly Transform Your Data

Load Your Data: Ensure you properly load your shapefile using Geopandas.

[[See Video to Reveal this Text or Code Snippet]]

Check Your Current CRS: Before converting, confirm your starting CRS.

[[See Video to Reveal this Text or Code Snippet]]

Perform the Transformation: Use the following command for conversion:

[[See Video to Reveal this Text or Code Snippet]]

Validate the Transformation: Check if the output coordinates seem reasonable given their expected projection.

[[See Video to Reveal this Text or Code Snippet]]

If Necessary, Convert to Degrees: Use EPSG:4326 if you need geographic coordinates.

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

The confusion surrounding coordinate transformations from EPSG:28992 to EPSG:3857 can primarily be attributed to misunderstandings about the nature of these systems. While the output coordinates may seem nonsensical at first glance, they are indeed