Buildings are a great use case for Hovermap. However, they do require careful planning, as there are many factors to consider. We recommend that you start your scan on the outside of the building. Once that is complete, you can then start scanning inside. Depending on the size of the building and the number of floors, we also recommend that you break up your scan into several smaller scans, with plenty of overlap between each scan.
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Scanning Building outside
The outside scan is the most straightforward part of the building scan. We recommend that you follow this process for the best results.
Step 1: Pre-mission checks
Complete the required pre-mission checks. For more information, see the Emesent Commander User Manual section.
Also, refer to the How does Hovermap navigate? section for more information on the how system automatically determines the most suitable navigation method based on the environment it is in.
Step 2: Perform your mission
Fly in Pilot Assist mode, and keep the drone within line of sight.
Fly so that Hovermap is facing the building at all times. Make sure that you thoroughly capture the outside of the building all the way around.
While scanning, check the live point cloud to ensure that your data is being collected correctly. Do this in the Emesent Commander application (refer to the Emesent Commander User Manual section for more information).
Avoid flying too high, as this may cause a SLAM slip. Fly as close to the building as possible, and try to stay within 20 m of the roof. The distance will be determined by the size of the building. With a smaller building, you could fly at 15 m, but a larger building might require more distance above to finish the scan in one flight (20 m to 30 m is a reasonable distance for a larger building). Anything further away is likely to reduce accuracy, especially if you want to colorize the scan.
Scanning Building Inside
Once you have completed the outdoor scan, you can then move indoors. This is the more complex part of a building scan. Indoor environments can present certain issues for SLAM-based scanners, as they contain many small apertures, such as doorways, that can cause issues if you don’t know how to navigate them correctly.
We recommend that you follow this process for the best results.
Step 1: Pre-mission checks
Complete the required pre-mission checks. For more information, see the Emesent Commander User Manual section.
Also, refer to the section of this manual How does Hovermap navigate? for more information on the how system automatically determines the most suitable navigation method based on the environment it is in.
Step 2: Plan your mission path
Break your inside scan down into small, practical sections, such as one room or floor at a time. It is best practice to keep your scan time short. We recommend 20 to 25 minutes. Make sure that your scan time doesn’t exceed 35 minutes.
If you are breaking your scan down into multiple sections, such as rooms or levels, make sure that you have a significant area of overlap between each scan so that they can be aligned during processing. If you are scanning multiple levels, make sure that you capture the stairwell between each level in every scan.
Step 3: Prepare your environment
Before you start the scan, make sure that all doors to rooms are open.
Make sure no people are moving through the area. People moving through your scan can cause drift, slips, and “ghosting”, which can ruin your dataset. Ghosting also means that you will have to do additional postprocessing of your point cloud to clean out the false points.
If you are georeferencing your scan, place GCPs around the scan area. Place four GCPs around the corners of your study area, and one in the center. Make sure that the square is slightly off-kilter (not perfectly square) so that, during processing, it is easier to identify which GCP is which. For more detailed information on GCPs, refer to the Georeferencing section.
Step 4: Perform your mission
Perform your scan according to the mission path that you have already planned. Make sure that you have plenty of overlap between each scan.
When moving through doorways or around corners, make sure that Hovermap can see both where it has been and where it is going. Do this by slowly moving sideways or backward through a doorway to introduce the new environment. When going around a corner, take the widest path possible and give Hovermap some time at the apex to see both the old and new environments together before proceeding. By doing this, Hovermap won’t lose track of where it is, and you will avoid a SLAM slip.
While scanning, check the live point cloud to ensure that your data is being collected correctly. Do this in the Emesent Commander application (refer to the Emesent Commander User Manual section for more information).
Finalize your inside scan by going outside and capturing the front of the building. This serves as an area of overlap between the inside and outside scans. Capture as much as possible of the front of the building. Ensure that you scan around the two corners to the left and right of the entrance.
Step 5: Process your data
Process your scan data using Emesent Aura. You can do this at the same time as you perform your next scan. Process the scan as follows:
Process and check each scan individually.
Align the inside and outside scans manually, as GPS won’t be available for the inside part of the scan.
Copy the translation matrix into Emesent Aura.
Process the combined scan.
Enable Individual output to allow you to load the scans both individually and together.
It is important to consider your computer’s ability to handle large datasets. The combined output might be quite large in size.
Once you have processed the scan, align the GCPs to the correct coordinates in your point cloud viewer. This will show you whether your capture methodology was successful and will help you to achieve the most accurate merge. If you are merging a set of individual point clouds and one of those scans is quite badly distorted, it can decrease the accuracy of the other scans. To help maintain accurate results, make sure that you don’t include poor-quality scans in your merge. When merging, choose the most accurate model to be the basis of your transformation matrices.