Mapping Corsica’s highest peaks with Emlid GNSS receivers

Defining what counts as a mountain might seem simple, but in places like Corsica, it’s surprisingly tricky. Many of the peaks listed on traditional maps don’t actually meet modern standards. That’s because older maps and tools sometimes mistook small bumps or nearby high points along a ridge for separate mountains. The Sostremetries team, a group of surveyors and mountaineers, set out to update the list using accurate elevation data and a clear, data-driven approach.

Their goal was to create the first topographically accurate list of Corsican summits (the highest points of mountains) above 2000 meters. To achieve this, they needed precise elevation measurements—far more accurate than what was available on traditional maps.

Redefining mountain mapping with Emlid gear

The Sostremetries team is a group of Catalan surveyors specializing in geodesy, topography, and cartographic analysis. With a passion for mountain exploration, they apply advanced surveying techniques to redefine elevation lists with scientific precision.

Their work integrates GNSS field surveys, LiDAR data, and digital terrain models to identify and validate summits based on objective topographic criteria. By combining traditional mountaineering with cutting-edge geospatial technology, Sostremetries has proposed updates to long-standing mountain lists, offering a more accurate approach to peak classification.

The challenge: inconsistent historical data

Most Corsican peak lists are based on 1:25,000-scale topo maps, which often overlook real summits or include minor bumps due to generalization. To bring clarity, the team turned to a long-standing question: What makes a mountain a mountain?

They followed the approach of Andrew Kirmse, former Google Earth engineer, who defined elevation, prominence, and isolation as the three key measures of a summit. These became the foundation of their list.

• Elevation (the height above sea level): only peaks over 2000 meters made the cut.
• Prominence (a summit rise above the surrounding terrain): a minimum of 30 meters was required.
• Isolation (the distance to the nearest higher ground): peaks had to stand at least 300 meters apart from any taller summit.

The specific prominence and isolation thresholds were selected to maximize the resemblance to the traditional list. Then, these thresholds were applied consistently across the entire island.

Applying these rules required collecting accurate elevation data, which led the team to integrate GNSS field surveys with remote sensing data.

Combining GNSS, LiDAR, and digital terrain models

The team used a combination of geospatial technologies to develop a new, more accurate list:

• LiDAR point clouds from the French mapping agency (IGN) provided high-resolution elevation data.
• Photogrammetric digital surface models (DSMs) also provided by IGN, played a key role in comparing terrain features across Corsica.
• GNSS field surveys validated and corrected remote sensing data.

While LiDAR and DSM models offered high-resolution mapping, they were not always reliable, especially in areas with snow cover or terrain artifacts. In these cases, GNSS receivers provided a necessary ground-truth reference.

Surveying Corsica’s peaks with Emlid GNSS receivers

To verify elevation and prominence values, the team carried out a focused field survey using Emlid Reach RS2+ and Reach RS3 receivers. Instead of measuring every summit, they targeted key points—both summits and mountain passes—where remote data was unclear or potentially inaccurate. This ensured precise elevation measurements where they mattered most.

Collecting raw data in rugged terrain with Reach receivers

Corsica’s mountainous landscape presented significant challenges. Many peaks required long treks across rocky terrain, with no access to the internet and real-time correction services. An independent and reliable method for precise GNSS elevation data was essential.

To address this, the team deployed Emlid Reach RS2+ and RS3 units in static mode, setting up receivers at each summit and key col for extended observation sessions. This approach allowed them to collect raw GNSS data over long periods, reducing errors caused by atmospheric conditions and ensuring centimeter-level accuracy.

Remote surveying with the Reach RS2+ base station

While many survey locations were far from established infrastructure, the team used France’s permanent GNSS network (RGP) for reference data whenever possible, keeping baselines within 20 km for accurate post-processing.

For summits beyond that range, they deployed Emlid Reach RS2+ as a base station at lower elevations. This setup provided a reliable local reference for differential corrections and also served to validate the consistency of Reach receivers. By comparing repeated measurements at known benchmarks, the team confirmed the stability and precision of their GNSS setup, even in Corsica’s most remote terrain.

Post-processing GNSS data in Emlid Studio

Since real-time kinematic (RTK) corrections were unavailable in many of Corsica’s remote regions, the team relied on Emlid Studio for post-processing static (PPS) corrections. This allowed them to refine GNSS data after fieldwork, achieving accuracy within just a few centimeters.

Additionally, they used Stop & Go post-processing in Emlid Studio, enabling efficient surveying of multiple points within a single session. 

With more than 65 summits and key cols surveyed, managing GNSS data at scale required an efficient workflow. The team initially processed each baseline manually in Emlid Studio but later adopted batch-processing techniques to speed things up.

While GNSS post-processing was done in Emlid Studio, the integration with LiDAR and DSM data was handled through GIS tools. This combined approach ensured consistent, high-quality elevation data across the entire Corsican dataset.

Validating peak elevations with Reach RS2+

The GNSS survey provided essential ground truth verification for discrepancies found in remote sensing data and traditional topographic maps. This verification step helped confirm key elevations where LiDAR data was skewed due to snow accumulations or surface artifacts. While most peaks were validated using high-resolution LiDAR, around 65 required GNSS field observations to ensure accuracy, raising the overall precision of the final list.

For example:

• Punta Rossa (Pic Von Cube) – Traditionally listed at 2247 m, but GNSS surveys confirmed it as 2284 m, correcting a 37-meter error.
• Capu di a Muvraghia – Previously recorded as 2015 m, but the true elevation was 2068 m, correcting a 53-meter error.

Explore Emlid solutions for accurate surveying

The Corsica 2000ers project demonstrates how combining LiDAR, digital models, and GNSS field measurements can significantly improve topographic accuracy. With Emlid Reach GNSS receivers and Emlid Studio, the Sostremetries team collected high-accuracy field data even in remote and challenging environments. The methodology developed by the Sostremetries team offers a scalable approach that can be applied to other mountain ranges worldwide, ensuring reliable elevation data for future research.

Learn more about Emlid solutions for precision surveying on our website.