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Christoph Prahl , Julia : i (fabian.wolfertstetter ) cannot edit the site above. Chris told me that i should fix the yellow target plate in the middle of the cross on the tripod. is that correct? does it have to be updated here?
also, consider changing the pitch angles in 15° steps and not 10° steps to reduce work
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Pre-Requisites
Please make sure that the drone settings are applied correctly, following manuals for each drone model:
Most Important:
Make sure that both Wide Angle RGB and IR camera have neutral Zoom settings (Zoom = 1.00)
Make Sure videos are recorded in the correct resolution:
RGB: 4k 3,840 x 2160
IR: 640×512
1. Components of the calibration set
1 tripod
1 tarpaulin
1 Acrylic plate with photogrammetric reference system
7-10 wooden bars with photogrammetric markers
4 connected wooden bars with photogrammetric markers to be mounted with the acrylic plate onto the tripod
2. Important advice
Please handle the whole equipment with care
In particular avoid scratches or dirt on the photogrammetric markers
The calibration should be carried out in a free space with at least 4 x 4 meters
The weather conditions need to be good, with sunshine but no wind
Any oscillation or movement of the equipment during the video capture will affect the data quality
avoid touching the equipment during calibration
avoid any wind
3. Material preparation
Unfold the tarpaulin and put it in a sunny place. This is important as the black parts should heat up in the sun so we can later see a contrast in the IR camera between the white and the black parts:
To unfold the wooden bars, release the nut from the screw and remove the top washer:
Put the bars in form of a cross with 90° spacing between the bars. Then carefully tighten the nut again (NO TOOLS REQUIRED):
Setup the tripod by spreading its legs and pull out the first inner stage to raise the tripod
open the clamp and mount the cross with the reference system to the tripod.
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Carefully close the clamp and make sure everything is tight. The cross should now be situated horizontally some 40-60 cm from the floor.
Arrange the bars in a star shape around the tripod as indicated in the next picture. The exact location is not that important, but the equal spreading is very important:
The distance between the outer slats should be about 2 meters:
Put the yellow acrylic plate with photogrammetric reference system on the floor between two bars:
4. Capturing the calibration video
Make sure that the camera settings have been adapted so that they are the same as if the drone was flying in the solar field (see drone settings in your document section in the app). You need to take a video to get the calibration data. You don´t need to fly the drone. It is necessary that you hold the drone in your hands above the cross in the middle and then move slowly around it.
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For each of the following steps, record an individual video |
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The center of the image must ALWAYS match with the middle of the cross during recording. |
First, center the drone at approx. 1.8 m above the reference system
start the video
put the gimbal pitch at 90° looking exactly downwards
and walk around the center, making a circle of 360°
Second, change the gimbal pitch to 80°
move one or two steps away from the center
center of image must match middle of cross
and walk around the center, making a circle of 360°
Third, change the gimbal pitch to 70°
move another step away from the center
center of image must match middle of cross
and walk around the center, making a circle of 360°
Fourth, change the gimbal pitch to 60°
move another step away from the center
center of image must match middle of cross
and walk around the center, making a circle of 360°
Sixth, change the gimbal pitch to 50°
move another step away from the center
center of image must match middle of cross
and walk around the center, making a circle of 360°
Seventh, change the gimbal pitch to 40°
move another step away from the center
center of image must match middle of cross
and walk around the center, making a circle of 360°
All this shall result in a video that can be uploaded using the volateq web app: https://app.volateq.de/analysis/new
5. Capturing the IR calibration video
Go to the tarpaulin. The black spots should feel warmer now.
Take the drone and set it to the IR camera.
Set IR gain mode to “HIGH“ for this calibration (M3T: gain -20°C - 150°C)
M3T: Do NOT activate “UHR Infrared Image” Mode for the IR Camera
Place the drone somewhere stable at about 2,20 meters above the tarpaulin. The drone should be positioned on an elevated, stable point with an edge. Simple examples are a car’s open trunk lid, top of a wall or roof, ladder, …
The drone must stand perfectly still during video capture:
not flying (too much vibration)
not hand-held (Too much shaking)
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The drone must stand still and must not move at all. Grab a short video, a few seconds are enough. With this, we will be able to create a look up table in our system to know which pixels in the IR range correspond to the one in the visual video.
Gimbal tilt must be in the range of -90 ° ↔︎ -70°
Sample Images look like this, the Tarpaulin must fill the entire IR image, but must not cover the entire RGB image!
RGB Sample Image:
IR sample Image:
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This will not work at all:
wrong tilt and not filling the entire frame
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IR sample Image (not optimal, upper image region is not filled with markers):
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