No other way?... To make that operation a little bit more "automatic" and for versatile situations?
As the Matrice 4 series is now, I cannot think of any way to make this automated.
Maybe DJI makes this available with a firmware update. You can always talk to DJI support and ask about this and then ask them to forward it to their engineers as a suggestion.
Some commercial laser range finders do have this feature, so it may be possible that a firmware update could make this a reality.
You could always hover, use the new AR marking feature to draw two lines over a road and then time cars as they pass the line.
Get the time it takes, feed this information to Google Gemini or Chat GPT and receive your answer.
A simple statement to Google Gemini such as: "It took a car 2 seconds to travel 100 feet, what is the car's speed?"
will produce, "The car's speed is 50 feet per second. In miles per hour, this is approximately 34 mph.".
