Calculating visual Height

Rchawks · Mar 9, 2020

The question pertains to setting the height in the app for RTH function. How do you arrive at that figure? Do you look at a tree or structure and make a guess or do you fly above and over gauge it. I realize this is easy for pilots who been flying a long time to make that guess. Not so easy for the new pilots, I wouldn't want to error on the wrong side of adjusting the RTH function. On the other hand I also wouldn't want to set it too high either, because of gusting winds higher up. I can also imagine that trying to fly over a tree is easier said than done due to depth perception depending on where you are standing. Also the farther away your drone is the more unknowns there are in case something goes wrong and RTH kicks in.. How do you do it?

bumper · Mar 9, 2020

If the winds up high are gusting and overly strong for the drone in use, best not to fly. To gauge RTH height over unknown height obstacles, set camera to zero declination, fly up looking over obstacle and read altitude on screen. I have a laser rangefinder that gives me height of obstacles, but that's overkill.

Rchawks · Mar 9, 2020

I've been very attentive to the wind and wind gusts at the height I will be flying. I haven't flown very high or far or way yet but that being said I'm just trying to be careful and learn slowly to get my basics down pact. Thank you for the tip!

sar104 · Mar 9, 2020

Rchawks said:
The question pertains to setting the height in the app for RTH function. How do you arrive at that figure? Do you look at a tree or structure and make a guess or do you fly above and over gauge it. I realize this is easy for pilots who been flying a long time to make that guess. Not so easy for the new pilots, I wouldn't want to error on the wrong side of adjusting the RTH function. On the other hand I also wouldn't want to set it too high either, because of gusting winds higher up. I can also imagine that trying to fly over a tree is easier said than done due to depth perception depending on where you are standing. Also the farther away your drone is the more unknowns there are in case something goes wrong and RTH kicks in.. How do you do it?

It shouldn't be an issue, because if you are maintaining VLOS then by definition the flight path home should always be clear. It can be an issue if you fly behind obstacles that are taller than the flight altitude AGL. If you have a BVLOS waiver or don't care about flight legality, then it depends on the obstacle. Terrain heights you get from GE or topos. Structures or trees you could estimate by climbing to be level with the tops.

bheiser1 · Mar 9, 2020

At first I’d fly over the tallest obstacle (almost always trees in my case) to see how high I had to go to get over them. After a while was able to estimate based on what the trees look like. I usually add something like 20-30 ft as a buffer. If the terrain is varied (like if some are on an uphill slope) I’ll estimate the add’l height from the slope & add that in. Tall trees in my area are around 150-165’...

slup · Mar 10, 2020

bumper said:
...To gauge RTH height over unknown height obstacles, set camera to zero declination, fly up looking over obstacle and read altitude on screen...

@Rchawks ... as @bumper said, set camera to zero pitch, fly then straight up ...

If you then as in the example below, at 18m see that the obstacles you are worried about (the tree line & that building in distance) are above the horizon ... then your drone are below the obstacles.

Here you have ascended a bit to 23m ... trees are now below horizon & are cleared, but not the building.

Now on 48m both the trees & the building are below horizon & you will clear them ... add then a safety, 10m perhaps, & you should be good to go.
(As you see, so are the horizon a bit hilly ... that means that your gauge height will be a bit high, but better that then to low.)

Fearless Flight · Mar 10, 2020

One way is to go up to say 50 feet. Then do a 360 and see where the tallest object is. Then stay pointed at that object and keep going up until you are above that object. Then add 10 feet or so to the height your screen is showing as the current height of your drone.

E90RAW · Mar 11, 2020

I utilize the M2P like a ruler, I level the camera and will take the drone up until at the top height of the object in question. Whether tree or cell tower(200 feet for towers). Make sure your height is zeroed at ground level prior to takeoff. Then add some buffer of several feet. Watch the controller as sometimes when turning/changing direction of the drone you are bringing it down slightly (same controller nob for height and direction). Also, the stated height on the controller can change over the flight and so you need to periodically re-zero on the ground by landing (at least that is my routine). After awhile you've pretty much mapped the area your flying in and know the measurements/heights. I have learned my lesson the hard way as visual estimation is subjective at best, and I have crashed M2Z due to my "overestimation" of my height on the trees.

DanMan32 · Mar 11, 2020

Assuming your terrain is flat, the horizon trick works regardless of gimbal angle.
If anything, you'll actually be a bit higher if gimbal is pointing below 0 degrees.

But if you want to know an object height by locating it at the center of your view, then gimbal will need to be horizontal.

apeel · Mar 14, 2020

slup said:
@Rchawks ... as @bumper said, set camera to zero pitch, fly then straight up ...

If you then as in the example below, at 18m see that the obstacles you are worried about (the tree line & that building in distance) are above the horizon ... then your drone are below the obstacles.

View attachment 96259

Here you have ascended a bit to 23m ... trees are now below horizon & are cleared, but not the building.

View attachment 96262

Now on 48m both the trees & the building are below horizon & you will clear them ... add then a safety, 10m perhaps, & you should be good to go.
(As you see, so are the horizon a bit hilly ... that means that your gauge height will be a bit high, but better that then to low.)

View attachment 96263

Hey Slup. So obvious and yet so brilliant!! Thanks for the explanation. The pics are very helpful!

Drgnfli · Mar 17, 2020

slup said:
@Rchawks ... as @bumper said, set camera to zero pitch, fly then straight up ...

If you then as in the example below, at 18m see that the obstacles you are worried about (the tree line & that building in distance) are above the horizon ... then your drone are below the obstacles.

View attachment 96259

Here you have ascended a bit to 23m ... trees are now below horizon & are cleared, but not the building.

View attachment 96262

Now on 48m both the trees & the building are below horizon & you will clear them ... add then a safety, 10m perhaps, & you should be good to go.
(As you see, so are the horizon a bit hilly ... that means that your gauge height will be a bit high, but better that then to low.)

View attachment 96263

That was a great explanation with "visual aides!" Thank you for the time you spent putting it on this forum! I never heard of that method before...

I found another way to check for obstructions (I think I found it on this forum). If the object you are approaching in the screen does not move to the left, to the right, or does not move below the center of the screen (turn on the "grid" on your RC screen), YOU ARE GOING TO HIT IT !!!

Rchawks · Mar 17, 2020

GadgetGuy · Mar 18, 2020

Drgnfli said:
That was a great explanation with "visual aides!" Thank you for the time you spent putting it on this forum! I never heard of that method before...

I found another way to check for obstructions (I think I found it on this forum). If the object you are approaching in the screen does not move to the left, to the right, or does not move below the center of the screen (turn on the "grid" on your RC screen), YOU ARE GOING TO HIT IT !!!