How Do I Use The Camera to Estimate the Height of an Object?

[AMann]

I also use Theodolite on my iPhone (the Op is using Android, so he’s out of luck) to measure the vertical angle. I also use the map feature in Theodolite to estimate horizontal distance. I then plug both numbers into a small spreadsheet on my phone to do the trig for height. Since the sensors in the iPhone need calibrated to improve Theodolite’s accuracy, I designed and 3D printed an artificial horizon to facilitate the calibration. This setup works great.

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Very nice! What are you using it for? I started using it for habitat analysis work when it first came out, and now with my students as a fun tool for math and science class projects.

 

[Ralph thompson]

There are two very simple ways to judge the height of obstacles.
1 - find a stick the length of your arm, hold your arm out straight & the stick vertical, walk towards the obstacle and when the top of the stick, yr eye and the top of the obstacle are aligned, you are then at the same distance from the obstacle as the obstacle is high. Just stride towards the obstacle and count the number of steps. Multiply by 3 and that’s the height in ft.
2 - standard procedures with every flight, fly straight up with the camera facing the obstacle. When the top of the obstacle touches the horizon, that is the height of the obstacle. I always yaw the drone slowly through 360 deg at that point to see if anything else in the area is higher.

 

[AMann]

There are two very simple ways to judge the height of obstacles.
1 - find a stick the length of your arm, hold your arm out straight & the stick vertical, walk towards the obstacle and when the top of the stick, yr eye and the top of the obstacle are aligned, you are then at the same distance from the obstacle as the obstacle is high. Just stride towards the obstacle and count the number of steps. Multiply by 3 and that’s the height in ft.
2 - standard procedures with every flight, fly straight up with the camera facing the obstacle. When the top of the obstacle touches the horizon, that is the height of the obstacle. I always yaw the drone slowly through 360 deg at that point to see if anything else in the area is higher.

I agree with #2, but as interesting as #1 sounds, you have some missing critical information such as knowing how far from your eye the stick is, how long the stick is and how you must match the bottom of the stick to the bottom of the target and the top of the stick to the top of the target. I think instead of measuring in feet, it would also provide a measurement in cubits

 

[Donnie Frank]

Here's the situation----There's a clump of trees in an otherwise open area where I often take off. I would like to know how high the tallest tree is. I could hover at what appears to be the top of the tree by centering its image on the screen and referring to the altitude readout, but unless the camera is pointing straight ahead and (more importantly) parallel to the ground, the readout would not be accurate. Is there a command in Go4 or Lichi which centers the camera so that it is pointing straight ahead and parallel to the ground?
TIA!

"Gimbal Reset" via either the C1 or C2 button. You can toggle between "straight ahead" and "straight down" (nadir).

D

 

[JAW]

"Gimbal Reset" via either the C1 or C2 button. You can toggle between "straight ahead" and "straight down" (nadir).

D

Thank you!

 

[AgentMIB]

Here's the situation----There's a clump of trees in an otherwise open area where I often take off. I would like to know how high the tallest tree is. I could hover at what appears to be the top of the tree by centering its image on the screen and referring to the altitude readout, but unless the camera is pointing straight ahead and (more importantly) parallel to the ground, the readout would not be accurate. Is there a command in Go4 or Lichi which centers the camera so that it is pointing straight ahead and parallel to the ground?
TIA!

As a FAA private pilot, one is trained a simple method in mountain flying whether you're above the approaching terrain (ie: mountain pass). In your case, set camera level and pointed to the tree.

Slowly fly towards the tree, building, antenna or other object.
1. If you see more objects appearing beyond the tree as you approach, you're above the height of the tree and will clear it.
2. If you see less objects as you approach, you're too low and will crash into it.

Increase altitude until you achieve #1 and you will know the safe altitude to clear height of an object.

 

[Earthman]

Very nice! What are you using it for? I started using it for habitat analysis work when it first came out, and now with my students as a fun tool for math and science class projects.

I use Theodolite for all kinds of stuff. I practice civil, geotechnical and environmental engineering, and do aerial mapping for our surveyors. It comes in handy. Here’s a photo where I used Theodolite to estimate the slope of a rock anchor in a retaining wall:



The anchor is 30-deg below horizontal.

I’ve also used it like a bearing compass to find my location on maps and site plans relative to features that I can see that also appear on the map or plan.

It’s a useful app.

 

[mooneyguy]

Provided there is a true horizon. There might be mountains. Or he might be on the edge of the earth...

If the drone is reasonably close to the tree the error will not be large: If there's a 5000' mountain 20 miles away (or a 2000m mountain 40km away...), the error caused by using that instead of the true horizon will be 1/20 of the distance from the camera to the tree.

If you're worried about that error (or want to have more fun), use the technique that airplane pilots have used for years to tell if they're going to clear a ridge: Fly slowly toward the tree at a constant altitude. If the tree appears to be falling away as the drone approaches, the tree is lower than the camera. If the tree appears to be rising up as the drone approaches, the tree is higher than the camera. When the top of the tree appears stationary in height relative to the distant background as the drone approaches, then the camera is at the same height as the tree top.

 

[Mikeg]

There really is a much easier way which doesn’t require the use of trigonometry (directly) or your drone. Simply get a piece of foolscap paper , Cut it down to a square shape, folded diagonally in half (that way each of the angles is 45° exactly) .You should now have an isosceles triangle with two 45° angles .
estimate the height of the tree and then walk that number of paces away from the tree. Now hold your triangle in front of you so that you are looking up the slope and adjust your position until it appears that the slope goes to the top of the tree. Now count the number of paces to the tree , Add two paces for your height and you have the approximate height of the tree. This is not exact but pretty accurate and very simple to do. Don’t risk your drone for nothing.
Of course this won’t work if you can’t walk in a straight line from the base of the tree.

 

[matth1000]

And the ground must be flat from the trunk of the tree to where you walk to.

 

[Alan O]

Thank you!

What drone are you flying?

 

[Andrew F]

There is a command, which you can assign to one of the buttons, which alternates the gimbal between pointing straight down, and straight ahead. When it returns to straight ahead, it is not only at zero degrees vertically, but is also centered horizontally, in case you have "swiped" the gimbal from one side to the other, using your finger.

So use that and you will have exactly what you want.

I use that feature all the time. Very handy.

 

[JAW]

What drone are you flying?

M2Z

 

[johnmeyer]

M2Z

Now that you've finally revealed what drone you are flying, I don't understand why you can't find the command to recenter the gimbal. It is available for all three programmable buttons: C1, C2, and the little mini-joystick. You will find these settings in the third item in the left column of the setup menu ("Remote Controller Settings"). The mini joystick is called the "5D Button" and the setting you want to assign is the "Camera Forward/Down" function.

I have the "down" action on the little joystick set to reset the gimbal: one flick down and the gimbal immediately goes straight down. The second flick down centers the gimbal and points it exactly horizontal, neither up nor down, and neither left nor right, but straight ahead.

Just what you asked for.

So all you have to do is turn the grid on, so you have a horizontal line across the display at the exact midpoint of the display. You then center the gimbal and climb the drone until the top of the tree is exactly under the centerline. Read the altitude and you will have your answer, to whatever precision the vertical portion of the GPS can give you.

As a side note, even after "selective availability" was removed many years ago (the military detuned the GPS so it couldn't be militarily used against us), GPS vertical (Z) accuracy improved dramatically, but is still much worse than its X-Y accuracy. However, if you can figure out how to feed a differential GPS signal into your setup, you can get accuracy to fractions of an inch. This is what surveyors use.

 

[JAW]

Now that you've finally revealed what drone you are flying, I don't understand why you can't find the command to recenter the gimbal. It is available for all three programmable buttons: C1, C2, and the little mini-joystick. You will find these settings in the third item in the left column of the setup menu ("Remote Controller Settings"). The mini joystick is called the "5D Button" and the setting you want to assign is the "Camera Forward/Down" function.

I have the "down" action on the little joystick set to reset the gimbal: one flick down and the gimbal immediately goes straight down. The second flick down centers the gimbal and points it exactly horizontal, neither up nor down, and neither left nor right, but straight ahead.

Just what you asked for.

So all you have to do is turn the grid on, so you have a horizontal line across the display at the exact midpoint of the display. You then center the gimbal and climb the drone until the top of the tree is exactly under the centerline. Read the altitude and you will have your answer, to whatever precision the vertical portion of the GPS can give you.

As a side note, even after "selective availability" was removed many years ago (the military detuned the GPS so it couldn't be militarily used against us), GPS vertical (Z) accuracy improved dramatically, but is still much worse than its X-Y accuracy. However, if you can figure out how to feed a differential GPS signal into your setup, you can get accuracy to fractions of an inch. This is what surveyors use.

Thanks for your input.

 

[Alan O]

Now that you've finally revealed what drone you are flying, I don't understand why you can't find the command to recenter the gimbal. It is available for all three programmable buttons: C1, C2, and the little mini-joystick. You will find these settings in the third item in the left column of the setup menu ("Remote Controller Settings"). The mini joystick is called the "5D Button" and the setting you want to assign is the "Camera Forward/Down" function.

I have the "down" action on the little joystick set to reset the gimbal: one flick down and the gimbal immediately goes straight down. The second flick down centers the gimbal and points it exactly horizontal, neither up nor down, and neither left nor right, but straight ahead.

Just what you asked for.

So all you have to do is turn the grid on, so you have a horizontal line across the display at the exact midpoint of the display. You then center the gimbal and climb the drone until the top of the tree is exactly under the centerline. Read the altitude and you will have your answer, to whatever precision the vertical portion of the GPS can give you.

As a side note, even after "selective availability" was removed many years ago (the military detuned the GPS so it couldn't be militarily used against us), GPS vertical (Z) accuracy improved dramatically, but is still much worse than its X-Y accuracy. However, if you can figure out how to feed a differential GPS signal into your setup, you can get accuracy to fractions of an inch. This is what surveyors use.

That was exactly what I was going to say.

The 5D button!

It should be the default settings, don't think you need to set it up again

 

[Skry]

One method I use is to line up the top of the tree with the horizon.

I think this is the simplest and most reliable way and i always do it before flying closely above objects.
Just fly you drone somewhere near the tree till top of tree alighes with horizon - than you know you are hovering exactly at the same altitude as the tree top.
If you are planning to fly close above the tree but pointing camera in another direction (not seeing it), than make sure to give yourself extra few m extra height

If you are filming the tree top than if top of the three is just below the horizon line and moving down away from horizon line when you are approaching it - it means you are above it. See my shot starting at 7th second:

 

[Chas2379]

???? Visual trig? All you need to do is... ..nevermind. Best you climb to the top and drop a long tape measure down.

Best answer yet.

 

[Chas2379]

Here's the situation----There's a clump of trees in an otherwise open area where I often take off. I would like to know how high the tallest tree is. I could hover at what appears to be the top of the tree by centering its image on the screen and referring to the altitude readout, but unless the camera is pointing straight ahead and (more importantly) parallel to the ground, the readout would not be accurate. Is there a command in Go4 or Lichi which centers the camera so that it is pointing straight ahead and parallel to the ground?
TIA!

Take a picture of a 5 ft woman standing next to the tree. Then cut and paste that picture on the tree until you get to the top. Now it will take a little math but I'm sure you can figure it out from here.

 

[johnmeyer]

The OP's original question reminds me of an old joke.

An engineer, an accountant, and a salesman were asked to measure the height of a building. After three days, they all presented their results.

The engineer said, "the height of the building is 82 feet, plus or minus a foot. I measured using a transit and used basic trigonometry."

The accountant than gave his answer, "what height do you want it to be?"

The salesman then presented his results: "the building is 82.73 feet high, exactly."

The people running the contest were stunned: "How can you be so sure?"

The salesman said, "I found the janitor who knew where the building plans were kept. I gave him twenty bucks and he let me photograph the original blueprints."