INTRODUCTION
Deciding which drone LiDAR system to get for drone surveying mapping is difficult, especially if it’s your first unit. Cost of a drone LiDAR package, although much lower today compared to just 18 months ago, still can get expensive. But cost should not be the only consideration, maybe not even the most important one. The performance should be carefully scrutinized, with other vital factors such as manufacturing quality and post-sale support. Fortunately, all RESEPI systems use the same high-performance tactical-grade Inertial Measurement Unit (IMU) developed and manufactured by Inertial Labs, tested and calibrated at our headquarters in Virginia, USA—allowing a streamlined process that reduces costs and increases the quality of the product.
We aim to help you find the best product that meets or exceeds your requirements while fitting into your budget.
We will discuss these two INS units further in a separate article. Let’s get back to the main question with those basics out of the way. Which RESEPI payload is best for you?
RESEPI LiDAR Components
Each RESEPI unit offered by Inertial Labs can be configured in multiple ways. There are three key hardware components in an integrated drone LiDAR system: The camera, POS/INS, and the Laser. A POS (Position and Orientation System) in terms of drone LiDAR is what some may know better as an INS (Inertial Navigation System), or a GPS-Aided Inertial Navigation System, to be more precise. There are two INS options for RESEPI, as shown in Figure 1: INS-B-OEM and INS-D-OEM.
SPECIFICATIONS COMPARISON
All differences between these two LiDAR models for drone surveying mapping come down to the lasers. Overall, the Livox Avia laser is capable of many projects, but the Hesai XT-32 delivers better data accuracy, higher productivity, and more real-life application versatility. RESEPI XT-32, therefore, is our top-recommended choice in this comparison. While reviewing the specifications on Laser Range, remember that the recommended flight altitude is between 50-100m AGL (Above Ground Level) to keep the most accurate data while covering the most surface area.
WHAT TO EXPECT
Coverage and Point Density
Coverage and point density are the most critical factors when comparing system performance. Coverage is the measurement that explicitly describes how gathered data points cover much surface area. Point density, however, measures how many data points you can collect within that surface area. As shown below, the RESEPI XT-32 returns lower density with a higher cover area, while the RESEPI Avia returns higher density with a softer cover area, depending on the set velocity. Remember that these tests took place excluding initial and final static alignments, convergence maneuvers, and sharp turns. Note that Hesai XT-32 natively has a horizontal Field of View (FOV) of 360° but was limited for a better side-by-side comparison of the performance of the two solutions for drone surveying mapping.
Cloud Comparison
Comparing a finalized cloud between both the RESEPI Avia (Figure 4) and RESEPI XT-32 (Figure 5), we can see that the RESEPI XT-32 outperforms the RESEPI Avia in terms of surface area coverage, accuracy, precision, and coverage underneath structures (specifically foliage), showing that it is the top performer. Each unit flown used the same conditions (flight path, camera shutter speed, INS, and velocity); the only difference was the laser used.
Point Cloud Density
Taking small sections from the same flight covered previously, we can see that the RESEPI XT-32 (Figure 6) could achieve a higher point cloud density than the RESEPI Avia (Figure 7). Blue indicates points gathered, and gray indicates that there is no collection of data points. We see a higher density from the RESEPI XT-32This because of the XT-32’s laser characteristics. Specifically, the Hesai XT-32 has a 360° horizontal FOV (Field of View) and a 31° vertical FOVF, which allows for layers of overlap between flight lines which increases cloud density to increase density. However, this only occurs when LiDAR passes are layered or overlapped. If it is a straight flight path with no overlap, the RESEPI Avia will result in a higher point cloud density. In Appendix A, you can find examples of these flight patterns with or without overlap.
IN-DEPTH: RESEPI AVIA
Lighter Weight
The Livox Avia has a clear weight advantage, as shown in Figure 2, at just below 500g versus the 800g of the Hesai XT-32. The RESEPI system integrated with a RESEPI Avia Laser weighs about 600g less than the RESEPI XT-32. Lighter weight results in longer adequate flight time and increases the selection of drone platforms by including those with lower payload lift capacity.
Concentrated Scanning Field of View
The Avia laser generates 240,000 pulses (single return) every second. Although this is lower than the 640,000 pulses/second (single-return) from the XT-32 laser, Avia concentrates all 240,000 measurements in a narrow 70.4° by 4.5° Field of View. At the same time, XT-32 spins the laser full 360°, making it possible for the Avia laser to produce higher ground point density (NPD).
In testing, however, it is shown that in many cases, the RESEPI XT-32 produces a higher density depending on the flight pattern. If the user makes multiple runs over the same land area while overlapping passes, the RESEPI XT-32 outputs a higher density. However, if it is just one single pass over a site, the RESEPI Avia outputs a higher density. In many circumstances, users will overlap their passes, in this case, putting the RESEPI XT-32 above the RESEPI Avia.
Lower Cost
The Avia laser costs less than the XT-32, not a significant amount, but meaningful when working within budget constraints. For the user, where a couple of thousand dollars means being able to bid or not on a job, the Livox AVIA will give a competitive edge.
Extra Possible Advantages to Consider
RESEPI Avia has some other advertised advantages but was tested by the engineers at Inertial Labs.
- Range. Avia has a published maximum detection range of 190m (10% reflectivity @ 100klx) vs. 80m from the XT-32 (10% reflectivity @ 100klx). In practice, however, the XT-32 delivers comparable or better data up to 120m with higher accuracy.
- Number of Returns. Avia can produce up to three returns per laser pulse vs. two returns by the XT-32. A 3rd return could be helpful in some situations, such as mapping ground under vegetation cover. However, as previously discussed, with a typical flight plan where grid lines are tight enough for an overlap of data points gathered on each pass, the XT-32 will outperform the Livox AVIA in mapping underneath vegetation.
- The Avia laser generates 240,000 pulses (single return) every second. Although this is lower than the 640,000 pulses/second (single-return) from the XT-32 laser, Avia concentrates all 240,000 measurements in a narrow 70.4° by 4.5° Field of View. At the same time, XT-32 spins the laser full 360°, making it possible for the Avia laser to produce higher ground point density (NPD).
- In testing, however, it is shown that in many cases, the RESEPI XT-32 produces a higher density depending on the flight pattern. If the user makes multiple runs over the same land area while overlapping passes, the RESEPI XT-32 outputs a higher density. However, if it is just one single pass over a site, the RESEPI Avia outputs a higher density. In many circumstances, users will overlap their passes, in this case, putting the RESEPI XT-32 above the RESEPI Avia.
Use Cases of RESEPI Avia
There are countless circumstances where a RESEPI Avia can stand out. Specific examples where this unit, in particular, stands out include:
1. When thin surveying objects: In this case, power lines are a great example, as they are extended with a small diameter and can often be hard to track with some lasers, but with the high point density on a single pass of the RESEPI Avia, the lines will stand out and appear more quickly. The RESEPI Avia would be a good and viable option in this circumstance, especially if there will only be one pass overhead by the scanner.
2. When drone surveying mapping areas higher than 120m above ground level: Some cases may require you to fly higher than 120m above the surface you are surveying, in which case the RESEPI Avia will suit you well. A couple of examples would include inspecting mountainous areas, cliffsides, or cities with tall buildings. Remember, however, that the higher you fly, the less accurate the data will be. In most cases, 120m will be more than enough to suit your needs for a flight mission.
3. When drone surveying mapping long distances: A few cases may require you as the pilot to survey runways, racetracks, or other long strips of land. These may be flown at higher speeds, requiring more points to be logged. The narrow Field of View of the RESEPI Avia allows for preserving point density at high speeds. Also, due to the lower weight of the RESEPI Avia, it, therefore, improves flight time by several minutes. Make a note that you can set an increase/decrease to your aircraft’s velocity before launch to match the mission flight length.
IN-DEPTH: RESEPI XT-32
Higher Measurement Accuracy and Precision
As was shown in Figure 2, the XT-32 delivers a 1cm range accuracy with 0.5cm measurement precision, while the Avia laser has a 2cm range accuracy and 1cm measurement precision. Environmental factors can alter laser-ranging accuracy and decrease as measurement distance increases. The XT-32 achieves its level of accuracy from 0.5m up to 70m under 30°C (86°F) ambient temperature. However, Avia’s published accuracy specs get tested at the 20m range under 25°C (77°F) testing conditions. The XT-32 outperforms the Avia on a broader temperature range in multiple height variations. With higher laser measurement accuracy, precision, and more robust signal strength and sensitivity, the XT-32 system will achieve higher practical project AGLs than the Avia system, with everything else equal.
With higher laser measurement accuracy, precision, and more robust signal strength and sensitivity, the XT-32 system will achieve higher practical project AGLs than the Avia system, with everything else equal.
360º Field of View
XT-32 spins all 32 laser channels in full 360° with three Frame Rate options: 5Hz, 10Hz, and 20Hz. This 360° Field of View makes the system more versatile, for example, scanning building facades, capturing assets’ vertical structures, and mapping forest stands and ground under trees. Refer to the section “What to Expect” for an example of this coverage.
Higher Surface Coverage
Thanks to the 360° Field of View, the RESEPI XT-32 system can cover a much broader sweep on each path, therefore capable of mapping a larger area every mission flight, delivering higher productivity. We have seen this perfectly in the previous “What to Expect” section.
Extra Possible Advantages
The RESEPI XT-32 has one convenient perk you may be interested in as a consumer.
Interference Rejection. As shown by Hesai on their product webpage, the RESEPI XT-32 uses proprietary interference technology to create an individualized tracking fingerprint for each laser, preventing errors from its lasers and “rejecting” noise from other nearby LiDAR units.
Use Cases of RESEPI XT-32
1. Surveying over umbrella-type objects or structures: These include trees, bridges, parking decks, or any other format with exposed spacing underneath. To better understand, think of a top-down view of a tree. You can see the top but nothing underneath. With the RESEPI XT-32’s 360° Field of View, it can reach and ping the underside of the tree to better visualize the structure as it surveys the area. Comparing it to the RESEPI Avia, we see it only has a Field of View of 77.4°, denying it access to the underside of most objects.
2. When surveying nearby tall objects or structures: These circumstances can include surveying a central park of a city, mountain-side valleys, or any other areas where surrounding objects may exceed or come close to the altitude of the flight mission. As we discussed earlier, you could use Avia’s range advantage to fly higher, but the accuracy and the point density would decrease. In these cases, the RESEPI XT-32 comes out on top since it can preserve high-accuracy data and point density while operating at the recommended altitude.
3. Where to pinpoint accuracy is a must: Some situations where this is the highest priority include higher altitude missions up to 120m and flights that check dimensions on structures. As stated, the XT-32 delivers a 1cm range accuracy with 0.5cm measurement precision, while the Avia laser has a 2cm range accuracy and 1cm measurement precision.
WHICH MODEL SHOULD YOU CHOOSE?
In conclusion, both models can complete almost any task regarding drone surveying mapping, thanks to the exact high-performance INS and high-quality manufacturing by us here at Inertial Labs. In this case, it will come down to which unit best fits the circumstances you will confront as the user. RESEPI Avia is an excellent option for those looking for slightly longer distance flights, higher point cloud density for single passes and thin structures, high speeds, and higher altitude missions. That said, the RESEPI XT-32 is the better payload, providing the most reliability in more situations requiring precise and accurate data, scans of objects at or above vehicle altitude, and heavy passes that offer data points to even the underside of many structures.
Please reach out to support@inertiallabs.com with any questions.
Appendix A
