Speed vs height above ground

I’ve been asked to create a video to document the condition of a road surface. Flying at about 35 feet AGL will give me an acceptable field of view. What ground speed would you recommend to avoid unacceptable blur? Will 60 fps produce better resolution than 30 fps? TIA

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The higher the shutter speed, the less motion blur.

It has nothing to do with the number of frames per second.
Also frames per second has nothing to do with resolution.


is the op talking frames per second or feet per second

60 fps and 30 fps are TYPICAL FRAME RATES.

Also 60 f/s equals 18.3 m/s, NO DJI drone can reach this speed in normal mode and only a few in sport mode.

Sorry for the confusion. Let me clarify. In terms of capturing detail with minimal blur, Ground Speed (feet per second or miles per hour) becomes significant when you consider subject distance (in this case, height above ground). At a given ground speed, the relative movement of a point past the lens is much faster when you are close to the ground than it is at a higher elevation. (Think about how much faster a race car seems to be going when it passes directly in front of you as compared with it’s apparent speed when you see it on the opposite side of the oval.) I am looking for recommendations (hopefully based on experience) for Ground Speed with the drone at about 35 feet AGL that will produce a video in which the details (cracks, potholes, patch repair) of a road surface will not be too blurry.

The 2nd part of my question was meant to be about frame rate, frames per second. I guess resolution (e.g. 1080p) was not the correct term to use. In the scenario described above, will 60 fps give better results (clarity, sharpness, definition) than 30 fps?

That depends on the bitrate the camera uses at those framerates.
If the camera uses the same bitrate for 30fs & 60fps, each frame taken at 30fps wil contain twice as much data and therefore of a higher quality.
Bitrate is bytes per second.
Framerate is frames per second.
Bytes(data) per frame equals bitrate devided by framerate.

No experience, only what Yordie allready wrote.
Most DJI drones have a 12 Mp camera and take 12 Mp pictures.
A 4k video frame is only 8.3 Mp.

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@Tom_Lesser It may be best to try this out for yourself to find out what works best for you. A little experimentation can go a long way towards getting the ideal result. You might start at 10 mph and then speed up or slow down until you are satisfied. Lighting will be critical if you hope to see imperfections like cracks in the road surface. Also you might want to use 60 fps and shoot at 4K for the best resolution and overall detail. Remember that both increasing the framerate and resolution will eat up memory on your SD card.

Thanks, Steve. I’m planning to do a few test runs at different ground speeds. I’ve done similar work walking slowly (maybe 1-2 mph) with a DJI Pocket 2 held about 3 feet off the ground and gotten acceptable results. At 35 feet AGL maybe tests at 4, 6, 8, 10 mph will provide enough feedback to settle on one particular speed. Video is so full of compromises. 4K is great but files are huge. Slower ground speed will produce videos that are longer/larger file size than a faster ground speed. And nobody wants to sit through playback of road surface documentation looking for problems so, from that perspective, shorter is better. Good quality/clarity in each “stopped” frame is desirable, so maybe 4K/60fps at a higher ground speed that doesn’t cause blur is best ???

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For sitting through large files, that are relatively slowly changing, using adobe time stretch to speed up or slow down the presentation time might be considered.

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Thanks for the suggestion, John. Had to Google “time stretch” and learned something new. The stuff I’ll be doing doesn’t require any fancy editing; it’s just for construction documentation. If a clip has to be searched, playback at 2x will speed things up.

FYI, I did a few test flights yesterday and settled on one set of parameters that I like pretty well … Phantom 4 Standard, 1080p at 30 fps, 35 feet AGL with gimbal pitch set at -70 and ground speed at 3mph gives acceptable results. With the gimbal at a slight angle the view is slightly wider at the top of the frame than at the bottom and it gives you a little more sense of direction that a straight-down view. 3mph is slow enough to see good detail, and gives time to hit the pause button if you need to take a closer look. 2mph was simply too slow and 4mph was hard to watch. @TriBar commented that 30fps will give higher quality than 60fps if bitrate is the same, but I haven’t found a bitrate spec. Still trying to wrap my head around bitrate and wondering whether I will know what to look for to discern a difference in quality if the bitrates differ.

@Tom_Lesser It sounds like you found the right speed and height, and 30fps should be fine at 3 mph. In the FPV community pilots typically use 60fps due to the much higher speeds attained when flying (generally high speed photography is used to capture a lot of action in a very short period of time which then allows the video to be played back in slow motion for analysis and effect, with examples being certain nuclear detonation films and lightning strikes).

I don’t expect to do any FPV work, so I think I’ll be content with these 30fps results. Thanks for your input.

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