Judging tree (and obstacle) height- How do you do it?

[Skybuyer]

I just (semi) finished editing a test clip that I did with a Litchi mission. As I look at it I have to wonder if I was too high and too chicken to fly lower as I am in many of my flights. I understand it is better to have a greater margin of error in obstacle avoidance rather than risk disaster. For the most part my concern where I largely shoot is mature trees. I tend to start at least 150' AGL, to stay above the trees, but it seems that this height may be a bit of overkill. As you may see from the photo below I didn't have anything really to clear but trees. I started waypoint 1 higher not knowing what wires might be strung near the highway, but I didn't see any in the video I shot. I don't seem to be very good (at least yet) of eyeballing height and want to know how the rest of you go about calculating minimium heights to stay clear of treetops and obstacles, yet get low enough for maximum impact?

I'll probably post the short video clip in the video display forum section once uploaded to cloud space.

 

[BigAl07]

When possible we actually fly up near the object and estimate the height from that. We do work in and around large Utility Poles and Stadium lights so we fly up to them and document the height.

 

[Deleted member 103366]

If you want to be 'low' and safe what about 2 flights, a reconnaissance flight were you measure and record the tree heights with the drone then the proper flight with 20 to 30ft of clearance added?

 

[Olav van Gerven]

I use two methods:

Pre-flight, I export the litchi-mission in KML and then open it in Google Earth Pro. Now I am able to see if there are any knowm obstacles

At the scene, if I am not sure about obstacles, I just start, get the camera horizontal and rise to the set altitude to make a slow 360. If I cannot recognize any obstacles, I take the bet that I can fly as planned.

 

[Skybuyer]

When possible we actually fly up near the object and estimate the height from that. We do work in and around large Utility Poles and Stadium lights so we fly up to them and document the height.

That seems logical and reasonable. How much margin for error do you allow if flying over something? At this point I still have difficulty knowing when something is "eye level" to the camera for measurement (or flying) purposes. I noticed that Google Earth Pro can give me information of object height when I hover over an object, but I'm not sure how reliable it is. It does seem to get things right. In the photoillustration below, Google Earth indicates the street level is 607 MSL and the top of the 4 story building is 653 MSL, the resultant calculation of the building's height being 46' AGL. The trees below via Google Earth are measuring about 40 feet, bordering a golf course.

Does this seem like a reasonable and accurate way of previewing the heights of obstacles?

 

[BigAl07]

I give at least 20'+. The aircraft isn't nearly accurate enough for me to feel comfortable any closer than that.

 

[Dave Maine]

The fly out and actually measure the height is the best approach. If the horizon is reasonably clear, you can line up the object of concern’s top point with the far horizon. When they line up, you are at the height of the object.

Set your flight height enough above the objects such that the intrinsic errors in the drone’s altimeter don’t put you below it.

This mission must be flown from the same takeoff point as the Litchi mission to work. The drone altitude is correct in Litchi only if you do this.

 

[theDRONEranger]

I use a range finder

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[Martinus]

The best ways are:

• Fly twice, first scouting, than official flight.
• Go up and make 360 degrees move with your drone, is less accurate for far away objects, but is extremely fast.
• Use Google earth, this is less accurate as it is not updated daily, so you can have new obstacles which were not yet included.

Please observe, that drones uses a GPS which have a 5 to 10 meter, (17 to 34 feet) error in either X,Y and Z directions, and the drone sometimes gets confused when he comes to close to objects, as it depends on air pressure to correct the estimated GPS height of flying. Only drones with RTK will have “exact” height.

So to be safe fly at least 40” over objects.

See the difference in flying in this video:

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RGDS,

Martinus
The Flying Dutchman

 

[Rupuze]

I just (semi) finished editing a test clip that I did with a Litchi mission. As I look at it I have to wonder if I was too high and too chicken to fly lower as I am in many of my flights. I understand it is better to have a greater margin of error in obstacle avoidance rather than risk disaster. For the most part my concern where I largely shoot is mature trees. I tend to start at least 150' AGL, to stay above the trees, but it seems that this height may be a bit of overkill. As you may see from the photo below I didn't have anything really to clear but trees. I started waypoint 1 higher not knowing what wires might be strung near the highway, but I didn't see any in the video I shot. I don't seem to be very good (at least yet) of eyeballing height and want to know how the rest of you go about calculating minimium heights to stay clear of treetops and obstacles, yet get low enough for maximum impact?

I'll probably post the short video clip in the video display forum section once uploaded to cloud space.
View attachment 111707

4 Ways to Measure the Height of a Tree - wikiHow

At a secret location somewhere in northern California, a tree named Hyperion has been measured at a world record height of 379.3 feet (115.61m)! Believe it or not, the measurement was made with an extra-long tape measure, but there are...

www.wikihow.com

 

[Skybuyer]

4 Ways to Measure the Height of a Tree - wikiHow

At a secret location somewhere in northern California, a tree named Hyperion has been measured at a world record height of 379.3 feet (115.61m)! Believe it or not, the measurement was made with an extra-long tape measure, but there are...

www.wikihow.com

Great idea. I decided to use geometry with a laser tape measure, which I may use along with the paper trick. I suspect that some of the trees I've encountered were 50-60' tall.

 

[Meta4]

Please observe, that drones uses a GPS which have a 5 to 10 meter, (17 to 34 feet) error in either X,Y and Z directions, and the drone sometimes gets confused when he comes to close to objects, as it depends on air pressure to correct the estimated GPS height of flying.

Your drone uses GPS for X & Y but uses a barometric sensor for the Y axis and does not make any correction.

 

[Rupuze]

4 Ways to Measure the Height of a Tree - wikiHow

At a secret location somewhere in northern California, a tree named Hyperion has been measured at a world record height of 379.3 feet (115.61m)! Believe it or not, the measurement was made with an extra-long tape measure, but there are...

www.wikihow.com

This is the way lumberjacks do it...They don't use a yardstick, but they hold their axe at the length of their arm:

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[Skybuyer]

This is the way lumberjacks do it...They don't use a yardstick, but they hold their axe at the length of their arm:

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Good video. I'm curious how, when using the laser, he calculated height measuring the bottom, then top from where he stood? I've got an inexpensive laser measurement device coming tomorrow. I suppose the paper trick would work easily when combined with the laser if you have enough space to back up or it's convenient.

 

[Rupuze]

NOt sure about the laser.
I don't think you even really need a tape measure...you can just pace it out (practice your pace first at home, then you'll have a pretty good idea [four paces = 12 ft, or whatever your pace is])
Also, the guy in the video should have added the distance from the ground to his eye--that would have been more accurate.

 

[DavidT_ NZ]

Your drone uses GPS for X & Y but uses a barometric sensor for the Y axis and does not make any correction.

Is that baro sensor on the Z axis ..... ? ?

 

[DavidT_ NZ]

I just (semi) finished editing a test clip that I did with a Litchi mission. As I look at it I have to wonder if I was too high and too chicken to fly lower as I am in many of my flights. I understand it is better to have a greater margin of error in obstacle avoidance rather than risk disaster. For the most part my concern where I largely shoot is mature trees. I tend to start at least 150' AGL, to stay above the trees, but it seems that this height may be a bit of overkill. As you may see from the photo below I didn't have anything really to clear but trees. I started waypoint 1 higher not knowing what wires might be strung near the highway, but I didn't see any in the video I shot. I don't seem to be very good (at least yet) of eyeballing height and want to know how the rest of you go about calculating minimium heights to stay clear of treetops and obstacles, yet get low enough for maximum impact?

I'll probably post the short video clip in the video display forum section once uploaded to cloud space.
View attachment 111707

I rely on the visual guide: F1 on the MA2 to flip the gimbal up and use the horizontal sight line to determine obstacle clearance. Then just fly up and over, to suit. I would never rely on a Google map! Safe flying ..... ????????

 

[Meta4]

Is that baro sensor on the Z axis ..... ? ?

Yes ... typo

 

[Skybuyer]

I rely on the visual guide: F1 on the MA2 to flip the gimbal up and use the horizontal sight line to determine obstacle clearance. Then just fly up and over, to suit. I would never rely on a Google map! Safe flying ..... ????????

Yeah... But you missed the big part of the issue. It was a LITCHI MISSION, designed at home with computer and Google Earth. Can't flip the gimbal up at home and can only rely on what you have. I made a mistake with RTH on a previous Litchi flight where I had it set to RTH, which makes a direct path back home at the altitude in the RTH settings. Mistakenly I used the published data on the height of the building and didn't check it on Google Earth first. The height of the building was 40' taller than published, because it was measured, starting at the top of an elevated base, rather than at ground level. Also, I had to learn that a lot of altitude is displayed in MSL, so one has to know what the MSL of the launch point is. Being right next to Lake Michigan, I was shocked to learn that Lake Michigan's shorline is roughly 578' MSL. I would have presumed it to be at sea level.

 

[AnzacJack]

I never fly an autonomous mission without first flying it myself. Recon is always the best. Slow and steady taking in every thing that may be an issue
The most important thing in aviation is a good situation awareness