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Mapping Uneven Ground using Map Pilot's Terrain Awareness Feature
6492 14 2016-7-21
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MapsMadeEasy
Second Officer

United States
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The world is not flat.
As of Map Pilot 2.1.0, the ability for the app to download terrain data for adjusting flight plans according to the terrain under them is available as an In-App Purchase.


Introduction
By downloading terrain information before planning a flight, Map Pilot will design the flight path to take changes in the ground elevation into account. Anyone who has tried to map uneven terrain knows that it is almost impossible to maintain consistent overlap when the Altitude AGL is changing with terrain. Consistent overlap leads to consistent GSD and higher quality map processing results.

This is not a sensor based solution and is compatible with all Map Pilot supported aircraft.

This image shows how a flight planned to take off at the bottom of a canyon will go up and down the canyon wall to maintain a consistent 60 meters above ground level altitude.

This video shows a comparison between a "flat" mission and a terrain aware mission. (Not the same mission in the video above)


Source of the Data
The Terrain Awareness feature uses SRTM (or Shuttle Radar Topography Mission) data that has been specially formatted for use with Map Pilot.
The SRTM data was collected in 2000. As of late 2015 the highest level of detail (30 meters/pixel) was made publicly available. This is a great example of how NASA's work helps people.

From USGS: "Endeavour orbited Earth 16 times each day during the 11-day mission, completing 176 orbits. SRTM successfully collected radar data over 80% of the Earth's land surface between 60° north and 56° south latitude with data points posted every 1 arc-second (approximately 30 meters)."

We are using the "SRTM 1 Arc-Second Global" variant. This data is available in the USGS EarthExplorer system.

More info:
Data Access Setup
In order to be able to access the terrain data with Map Pilot, a valid Terrain Data Access Token must be entered in the settings. Think of an access token as a password that allows the app to download the data.

To get the Terrain Data Access Token you will need a Maps Made Easy account. Once you are logged in to your Maps Made Easy account, go to https://www.mapsmadeeasy.com/profile on your mobile device and copy the value in the "Map Pilot Terrain Data Access Token" box so you can paste it into the Map Pilot settings box. If the "Map Pilot Terrain Data Access Token" entry is blank on the Maps Made Easy page, push the "Request Token" button to get one. If at any time you need to change your token to keep it secure you can push the "Request Token" button again to get a new one.


Terrain Data accesses are tracked by the Maps Made Easy system and are monitored for scraping or abuse. Accounts found to be associated with bulk download of the data will be terminated.

Considerations
With this new capability comes a few more things to think about when planning a mission. Due to limitations in the aircraft, the DJI SDK, the source data and real world obstacles any terrain aware flight should be carefully reviewed and verified before taking off.

Return To Home - When the RTH button is pressed on the remote or any other event that triggers a Return-to-Home occurs, the aircraft will ascend to the currently set Return-to-Home height if it is higher than its current altitude and proceed in a straight line to the takeoff location. The thing to consider here is that if, for example, you fly up and over a mountain and you are down on the other side back near your currently set return to home height and an RTH event occurs, the aircraft will fly in a straight line back to the takeoff location and directly into the mountain. This shouldn't be done because the flight would violate line of site requirements but it is still possible to send your aircraft there.
To combat this, all terrain aware flights will automatically adjust the Return to Home height to be 60 meters higher than the highest altitude encountered in the current flight path (if possible). Even if the aircraft is right next to the takeoff location when this occurs and is only 60 meters over head, it will ascend to higher than the highest point, come home and descend.

TL;DR - Don't fly up and over stuff because the return to home function wasn't really designed for these kinds of scenarios and there isn't anything Map Pilot can do about it.

Maximum Flight Height - DJI limits the height an aircraft can fly to 500 meters with respect to the takeoff point. A warning message and a red line will appear in the elevation plot to show the areas that are over the 500 meter limit. When a red line is present you will not be able to accept the terrain adjusted flight and take off.



Minimum Flight Height - Flight below the takeoff level is much harder to maintain a solid RC link for. A warning message will show and a yellow line is drawn to show the takeoff level.



Source Data Limitations - 30 meter pixels are HUGE. This is the highest resolution elevation data that is available. Look around you and imagine that everything was turned into flat 30 meter squares. There is certainly some data loss.

Date of Collection - This data was collected in the year 2000. If a mine pit was dug before that it may show up. If it was taken after that, it will not.

Unrepresented Obstacles - A utility pole, for example, will not show up. Skyscrapers may show up but the 30 meter granularity will cause issues for the accuracy of the height of the building and the area surrounding it. A vertical cliff face will be located plus or minus 30 meters. These are examples of vertical features that will not be well represented due to the size of the data samples and how it was collected.

Missing Data - 99.9999999% of the supported area is well covered. The data is MOSTLY fine. There are areas where the where the radar was unable to get a reading that have "voids". These empty data locations are in areas where the data has not been fully processed by NASA and are generally in areas of deep ground features or glaciers. In the presence of a "void", Map Pilot will use the last known good elevation. This is the safest course of action since these voids usually occur in deep places the aircraft shouldn't be going to anyway. The voids are usually small and Map Pilot attempts to overestimate the altitude.

Flight Planning
The use of the Terrain Aware planning tool is the same whether you are connected to the aircraft or not. The flight path definition is the same as it always has been except now when you tap the Terrain Aware button it will download the elevation tiles from the surrounding area and calculate the optimal flight path based on the terrain under the defined line. If the planned flight violates the various limits in some way or you would like to adjust it, tap the Terrain Aware button again to hide the plot and tap it again to recalculate.
NOTE: Making changes to the flight plan while a terrain plot is showing will not make changes to the terrain plan.


Flight Review
Touching and sliding a finger on the elevation plot will draw a light blue dot on the map that corresponds with the location of the touched location. This can be used to check the intended flight path and verify that the elevation that is shown in the plot is what the user sees in the real world.



Flight Execution
After planning a flight and reviewing it to make sure that everything looks good, the Upload button will get pressed to start the final flight path calculation step. When Terrain Awareness is enabled, there is a prompt for whether or not to execute a terrain adjusted flight. If "No" is selected, a normal flat flight will be programmed at the designated altitude. When "Yes" is selected, one final profile look up will be executed along the path. Then the user will have the opportunity to Accept or Reject the proposed flight profile. Rejection will allow the user to make further tweaks. Accepting the propose flight will upload it to the aircraft. Terrain Aware flight is started the same as usual. During flight the plot will be available by toggling the Terrain Aware button. Hiding and reshowing it will not cause a new profile calculation during flight. The orange vertical line shows the current progress along the flight path and shows the current elevation information for aircraft's location (red triangle).




2016-7-21
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greyphantom2
lvl.3
Flight distance : 787474 ft
New Zealand
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The terrain awareness looks great but in the Terrain Aware Flight Demonstration video it shows a Motion Blur value and for pretty much the whole mission it is a large value shown in red.
How can that be controlled, because it is obviously not desirable?
Cheers
Caleb
2016-7-21
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MapsMadeEasy
Second Officer

United States
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That video was taken using the simulator function so it was actually sitting on the desk. This is the only way we have come up with to take high quality video screen captures. To get the high quality video we plug into the port on the bottom of the phone to record it. Let us know if you know a better way other than using the P3 Standard's WiFi connection which lets us plug in but then we have to fly with a Standard which has its own issues.
2016-7-21
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xH0PELESSx
lvl.2
Flight distance : 640200 ft
United States
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   How much more difficult would it be to allow the app users/operators add their own DEM to use the Terrain Awareness feature? This would tremendously improve image resolution and the efficient of the flight and terrain mapping. I am guessing the Maps Made Easy guys understand the question but for the conversations sake lets say we fly a specific area using the NASA DEM, using GCP's and recreate the surface in post processing, then take the recreated DEM and add that to the app. The resulting 3D surface recreation would be the most accurate surface you could create using this collection method, especially if it's a recurring flight. I'll beta test it for you!

Thank you in advance,

2016-7-28
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MapsMadeEasy
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United States
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xH0PELESSx Posted at 2016-7-28 14:59
How much more difficult would it be to allow the app users/operators add their own DEM to use the ...

Thanks for the good question.  Map Pilot is not downloading raw DEMs since they are so big. We are heavily processing the DEMs to minimize the data required to be downloaded for offline storage.

In general, the Terrain Aware flight will keep the flight path within 5% of the specified AGL value so there is already a bit of variation. The variation is limited enough such that it won't adversely affect the overlap while not requiring too many waypoints.

We are considering using Maps Made Easy elevation layers as a source for the Terrain Awareness feature despite the fact that it represents a bit of a chicken-or-egg situation. Using a higher resolution DEM source alone will not affect the resolution or accuracy of the final product at all. Now if that DEM has information about objects like buildings or trees that is not in the NASA data it could affect things. Using a MME terrain layer as a data source would allow for lower terrain aware flight but we will have to see if there is enough demand to justify the addition of this feature.

  
2016-7-29
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xH0PELESSx
lvl.2
Flight distance : 640200 ft
United States
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Greetings,
   Doing some 'in-depth' verifications (not that you asked for it) using the 'Maps Made Easy' app and the terrain awareness option. So far so good. I will be doing a comparison of the same flight location using the same app with the terrain awareness option enabled and disabled. The area in questions has some decent undulating , mountainous terrain. I have ground-proofed the area and added a dozen GCP's to verify the surface reconstruction in the software I use. I will process both flights and look at the standard deviation of the surface, sanity points and GCP's.

2016-8-2
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Machoman
Second Officer
Flight distance : 1036959 ft
Austria
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"Minimum Flight Height - DJI does not allow for waypoint flight below the takeoff point."

Since when? With which firmware did DJI silently force this new limitation. I have missions below 0 and they did work last year.

I am just goind to the mountains next week and have many missions below 0. If it turns out DJI changes the abilities of the Inspire without warning or nitice I will go to my dealer give him that crap back and sue immediately for a full refund with my law insurance. Except DJI agrees to put it back to a firmware where it has not been a problem. I have really enough of this!
2016-8-2
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Machoman
Second Officer
Flight distance : 1036959 ft
Austria
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I just tested it with -3m and luckily it worked. So for me this statement is not correct:

Minimum Flight Height - DJI does not allow for waypoint flight below the takeoff point. The terrain can go below the takeoff point but the aircraft cannot. A warning message will show and a yellow line is drawn to show the takeoff level. The flight cannot be accepted until all flight is above the takeoff point.

However I am using Inspire FW 1.5 with RC FW 1.3 and IF DJI put new limits regarding this in newer firmware I would like to know it to prevent that I would occasinally come to the idea to try an firmware update.
2016-8-3
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MapsMadeEasy
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United States
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xH0PELESSx Posted at 2016-8-2 12:33
Greetings,
   Doing some 'in-depth' verifications (not that you asked for it) using the 'Maps Made E ...

Cool stuff. If you need some processing points on Maps Made Easy we can provide them in exchange for allowing us to use it as comparison samples if it turns out well.
2016-8-3
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MapsMadeEasy
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United States
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Machoman Posted at 2016-8-2 14:39
"Minimum Flight Height - DJI does not allow for waypoint flight below the takeoff point."

Since whe ...

Were these waypoint missions or just free flying? You can free fly below the takeoff point just fine.

In our test flights with the up to date firmware on a P4 we have seen the aircraft just stop and hover at about -2 m. According to the programmed flight path it would have continued down to -30 m.

We fully understand your frustration but also understand DJI limiting this. DJI is always adding new safety checks and fixing issues as capabilities are explored and new problems arise. A simple programming mistake would likely plow the aircraft into the ground if this limit was not there. There is not currently any SDK error thrown when programming in a flight that goes too low so Map Pilot is just not allowing the flight.

Allowing flight below the takeoff point is a really fast way to drop RC control and out of line of site unless you are right on the edge of the drop off.
Most of our validation does occur in the simulator because we can't spend 10 hours a day outside testing but this is the behavior we have seen. Regardless of whether DJI limits it or not we think it is a sensible restriction and Map Pilot will likely continue to use it.
2016-8-3
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Machoman
Second Officer
Flight distance : 1036959 ft
Austria
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MapsMadeEasy Posted at 2016-8-3 17:43
Were these waypoint missions or just free flying? You can free fly below the takeoff point just fi ...

Of course I am speaking of waypoints I use Litchi for this.

Then here is the Inspire forum no idea how the P4 behaves it may be the same or not.

I hope you dont test in the simulator as the simulator actually makes it enless slow as it cannot go under zero.

I am shocked how you try to defend this gamebreaker by DJI. Actually a simple programming mistake could also fly the aricraft into the ground without this senseless limit except in the simulator where the ground is flat and always at zero.And how much more likely is you fly into a tree a building or power lines instead of the ground? As the P4 is not necessarily heading forward the front sensors will also not help though they are speed limited anyway.

Even more dangerous! What is you loose connection 2km away and the nex waypoint is at -50 and ist STOPS and HOVERS there? Will it trigger RTH or will it try to finish the mission hoovering until the battery ends? What a joke behaviour. And you cannot test this in the simulator as this reminds on 1980 Atari and you cannot even load terrain maps or set starting altitude.

Are cars limited to 100km/h for all because there are some blind pensionists out there who cannot handle even this?

There is really no excuse for such a restriction and when I buy a drone advertised for waypoint flying which is NOT be able to fly with AGL inputs then I obviousely can not expect and accept such limits.

And if such limits are imposed later without warning and cannot be reverted then it sure will go back for a full refund under EU legislation.  
2016-8-3
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MapsMadeEasy
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United States
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Machoman Posted at 2016-8-3 09:35
Of course I am speaking of waypoints I use Litchi for this.

Then here is the Inspire forum no ide ...

Perhaps you should test it yourself before flaming away at DJI... Maybe it is working for you as you have suggested with your -3m test and we are mistaken. We will need to verify outdoors before changing our limitations. This is something we saw in the simulator and it seems like a logical limitation for maintaining line of site. We don't have access to anywhere we can legally do this test as a commercial entity and our legal flyers are not scheduled for testing for a bit.
2016-8-3
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Machoman
Second Officer
Flight distance : 1036959 ft
Austria
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MapsMadeEasy Posted at 2016-8-3 19:47
Perhaps you should test it yourself before flaming away at DJI... Maybe it is working for you as y ...

Its not that easy. There is another thread here were DJI-Ken confirms (beginning 2016) that waypoints under zero are not possible however some software seems not to have this problem.

So there actually may be some newer firmware which does not allow this and if not DJI will probably see this soon as a bug and "fix" it like the 500m alt limit which makes it impossible now to fully legally!!! fly up a mountain.

I obviousely CANNOT test newer firmware as it would brick my plane as it is impossible to revert it and restore full functionality. Be aware that its a lie that you can downgrade one step as they say. There are some part of firmware which you cannot downgarde anymore - I had this problem when ESC 1.11 ruined the performance and the downgrade did not reinstall ESC 1.08 as it should have done.

So thats why I can only ASK which firmware version is starting with this new limitation.
PS: Really? You are making an app for the Inspire but you cannot test how the Inspire works? Its not legal for you to go to a mountain fly 100m and set a point at -20m there? In most countries autonomous flight is allowed if you can regain control anytime. If there is a difference commercial or private no one says you must test this commercial.
2016-8-3
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MapsMadeEasy
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United States
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We were able to have a beta tester test whether or not waypoint flight will occur below the takeoff point. An unrestricted version of Map Pilot was able to fly below the takeoff level. We are considering removing the enforcement of not flying below the takeoff level in the next release. The pilot did note that the RC connection got a little funky so that is something that will definitely have to be watched.
2016-8-4
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barrub3d
lvl.2
Flight distance : 53333 ft
Italy
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here where i live , italy, i read this message "terrain data is only available between 60° north....."
so i can't download terrain data?
2017-4-3
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