LiDAR vs. Photogrammetry: The Ultimate Showdown for 3D Mapping (2024)

LiDAR vs. Photogrammetry: Which is More Accuracy?

When choosing between LiDAR and photogrammetry for geospatial surveying, the debate inevitably centers around accuracy. Both methods offer reliability when executed meticulously.

To discern their comparative strengths, a closer examination of absolute and relative accuracy is essential.

Absolute (Vertical) Accuracy

Absolute accuracy gauges the precision of an object's or feature's position on the Earth's surface in mapping data. It ensures the alignment between mapped points and their real-world geographic coordinates.

Relative (Vertical) Accuracy

Relative accuracy measures the precision of the positional relationships between different objects or features in mapping data. It assesses the accuracy of the relative positions of points within the same scene, regardless of their absolute position on the Earth's surface.

LiDAR Accuracy

LiDAR boasts high precision, with an anticipated ranging accuracy of 0.5 to 10 millimeters relative to the sensor. Mapping accuracy reaches up to 1 centimeter horizontally (x, y) and 2 centimeters vertically (z).

Point cloud density, the number of points per unit area measured by LiDAR, is key to accuracy, with higher densities yielding more precise maps.

A notable example is the JOUAV CW-25E VTOL UAV equipped with PPK and RTK modules, carrying the JoLiDAR-1500.

This setup generates highly accurate, true-color point clouds with a point density ranging from 50 to 200 points/square meter, providing a typical absolute accuracy of 2-3 cm vertically.

Mounting the JoLiDAR-1500 on a multi-rotor vehicle like the PH-20 further enhances point density and resulting point cloud accuracy.

Flying at low speeds and low altitudes, this configuration achieves point densities between 70 and 500 points/square meter, enabling measurements at 1-centimeter intervals and achieving an absolute horizontal accuracy of about 1 centimeter.

LiDAR's accuracy is attributed to laser pulses directly measuring distances, eliminating errors in manual measurements.

This, coupled with integration with GNSS data, helps provide a high level of vertical accuracy for your digital terrain maps.

LiDAR excels in achieving absolute accuracy, making it an ideal solution for creating realistic models of the bare earth by accounting for elevation and vegetation. With its high data point density, surveyors can generate reliable data sets, and the laser pulse rate plays a crucial role in this.

For instance, a higher pulse rate, such as the JoLiDAR-1500's collection of 1.8 million points per second, allows for more detailed models, reducing the number of flights needed to cover a specific area.

However, it's important to note that LiDAR systems are complex, with various components each contributing to accuracy.

Ranging errors in LiDAR sensors, horizontal and vertical position errors in GNSS, roll, pitch, and heading errors in INS, and other factors need to be considered.

In conclusion, despite complexities and various factors affecting accuracy, LiDAR generally outperforms photogrammetry in producing more detailed and accurate scans. The precision and versatility of LiDAR make it a preferred choice for intricate mapping applications.

Photogrammetry Accuracy

However, this is not to say that photogrammetry is not an accurate measurement solution.

Certain UAV photogrammetry systems can deliver outputs with horizontal (x-y) accuracy as fine as 1 cm (0.4 inches) and elevation (z) accuracy within the same range.

Particularly in areas devoid of dense forest canopy, photogrammetry outshines aerial LiDAR in terms of horizontal accuracy.

Now, achieving such precision isn't a walk in the park. You need specialized payloads armed with the right image sensors and lenses to capture the nitty-gritty details. It's not just a pixel game; it's about finding that sweet spot between sensors and lenses.

Even two cameras flaunting the same megapixel count but with different-sized sensors can dish out different levels of image quality and accuracy.

Optimal accuracy also relies on meticulous mission planning and post-processing. A well-planned mission with adequate image overlap enhances precision and facilitates superior error correction.

High-end UAS, coupled with specialized mission planning and post-processing workflows, play a pivotal role in ensuring the collection of high-quality data that translates into accurate results.

Nevertheless, without the aid of ground control points or RTK- or PPK-enabled UAVs, achieving absolute accuracy in photogrammetry becomes challenging. Shadows, occlusions, and the texture of the surveyed object are additional factors that can impact photogrammetric accuracy.

When all the necessary elements align, photogrammetry excels in terms of relative accuracy.

In contrast, LiDAR stands out by not necessitating ground control points for accurate data acquisition. This stands as a distinct advantage, especially considering the time-consuming nature of setting up GCPs.