Mapping a Polygon Comprising Above 100 Waypoints

1

Using my Mavic 2 Pro, I decided to try my hand at drone mapping, with the intent of “stitching” the hundreds of pictures taken by the drone is it flew a lawnmower pattern, using Web ODM, to create 2D and later 3D maps of an area.

Starting with the free utility to create the flight path called ancient land at this website https://ancient.land I drew a polygon around the area to be mapped, and set the altitude at 168 feet AGL, with the overlap at 70%.

Then I watched as over 200 waypoints materialized on my screen in the classic lawnmower pattern. Exporting that mapping mission file to Litchi Mission Hub was easy, as was setting the camera to take a still picture every 5 seconds.

Then came the moment of liftoff for the mapping mission. I decided to try out my Samsung tablet so that I could use the Android version of Litchi for the first time, after using my iPad’s IOS version of Litchi for hundreds of previous Litchi missions.

As the drone loaded up the mission before takeoff, I saw an on-screen alert warning that the drone would “interrupt” the mapping mission when the 99th waypoint was reached, so that the remainder of the mission, totalling about 221 waypoints, would load. Disconcertingly, that on-screen message also stated that the drone MUST be in signal range when that mapping mission interruption occurred.

To ensure that there was NO break in signal, I moved closer to the area I was mapping, until the drone was within line of sight. Before I was able to approach within line of sight of the drone, the signal disconnected when the drone was less than 200 yards away, as compared with the Litchi screen only starting to glitch at half a mile away when I used the IOS version of Litchi on my iPad.

I became even more nervous when I was able to see the drone flying the grid mission less than 100 yards out, because the red “Disconnected” banner STILL showed on the Android Litchi version’s screen. At that point, I decided to end the experiment by switching to sport mode, and landing the drone after it had completed less than 10% of the mapping mission’s projected elapsed time of 35 minutes, which the Mavic 2 Pro would have flown under the power of an extra-range Ali Express non-DJI battery.

Before I set my Android Samsung tablet aside and revert back to using my iPad’s IOS version of Litchi for another trial run of the mapping mission, I would like to ask a question about what I can expect the drone to do when it reaches the 100th waypoint of that mapping mission.

Since Litchi issued a warning that the drone MUST be in signal range of my controller when there is a break in the mapping mission, would I be correct in assuming that I will be required to initiate the download of the remaining waypoints once the drone reaches the 99th waypoint? What exactly will occur at the 99th waypoint? Will the drone go into a hover and present me with a prompt to upload the next 100 waypoints? Or will the drone Return to Home before prompting me to upload the next 100 waypoints?

My other question is why the signal range of my controller is so much shorter when I use my new Samsung Android tablet, as opposed to the far greater signal reach I became accustomed to seeing when I used my iPad for drone flights with Litchi’s IOS version. Is it possible that the Android version of Litchi attenuates the signal of the RC controller in some way?

2

If you are flying over relatively flat terrain, you can eliminate the waypoints along the flight corridors. In other words, only have waypoints at the beginning and end of each turn.

Most of my mapping missions have less than the 99 waypoint limit and still cover a lot of acreage.

Since you already have the mission planned in Litchi, you can delete the midpoints manually.

In Ancient.land, you can adjust the Z-check parameter and eliminate the waypoints along the paths. Then import the CSV file into Litchi and finalize your Mission Settings (Photo interval, etc)

1 Like
3

This is good news that I am glad to hear, Sam_G, and I thank you for taking a moment to explain how I can lower that waypoint count without losing resolution in the resultant imagery. I will give this idea a try before I run this mission again later today, after this next tropical rainstorm has passed through the area.

Once again I thank you for this response. I am sure I’ll have more enquiries as I delive into this new aspect of drone flying.

4

The reason for having midpoints along the flight paths, is to adjust the flight altitude and keep your bird from possible crashing into a hill.
Flight altitudes are based on the setting of each waypoint.

Example:
If you have property that has a mountain in the middle, and you only have waypoints at the beginning and end of each run, your drone will fly straight and level without adjusting for the terrain changes.

But, if you have a waypoint at the top of that mountain and have ‘Above Ground’ checked for waypoints, the drone will gradually climb to the top of the mountain then descend to the lower altitude on the other side.

Lots of discussions in this forum and on Wes’s site here:

1 Like
5

I had a couple of close shaves in my earlier Litchi waypoint missions when I set the altitude at certain waypoints a tad too low. On two occasions while viewing footage after my Phantom 3 Standard arrived from a BVLOS mission, I watched as the drone just barely cleared treetops by inches.

Now I am very careful to be sure altitudes are all set with the above-ground level box checked.

1 Like
6

This quotation is from Vico in a 2022 discussion about the 100 waypoint limit of DJI Go drones. " .You can do missions with more than 99 waypoints with all drones.
For older drones (the ones that use DJI Go as main app) which are limited to 99 waypoints in their firmware, Litchi will upload the first 99 waypoints, then once the drone has completed that mission, Litchi will upload the next 99 waypoints, etc until the end of your mission. For this to work, whenever Litchi uploads a mission, you need to be in signal range of the drone. Internet is not needed."

I just have two follow-up questions about the 100 waypoint limit.

  1. Does my Mavic 2 Pro, which uses DJI Go4, have this 100 waypoint limitation that Vico described as being a limitation of older DJI Go drones?
    . .

  2. If a waypoint mission is flown that has more than 100 waypoints, will the drone stop and hover in place at the 99th waypoint while the next 100 waypoints are uploaded from the RC controller’s signal, or will the drone RTH and await the loading of the next 100 waypoints only once back at the launch location?

  3. Finally, if there is NO signal connection between the RC and the drone when the drone reaches the 99th waypoint of a mission having more than 100 waypoints, will the drone RTH immediately, or will it simply hover in place until the battery drops to the level that a forced landing occurs? .

7

Yes. The Mavic 2 can only load 99 waypoints (98 subsequently) at a time.

Yes

I don’t know. I’ve never flown beyond signal range when flying that type of mission.

1 Like
8

These confirmations help clear the fog, Wes, and l am grateful to have fewer variables to speculate about. Since the process of downloading a second batch of 100 waypoints would consume a fair amount of battery power while the drone hovers in place, I am now thinking of raising the altitude of the grid pattern flight to reduce the number of waypoints before transposing the flight to the Litchi Mission Hub .

Since I have a Mavic 2 Zoom, I can increase the altitude from 168 feet AGL to maybe 250 feet AGL so that fewer than 100 waypoints are generated, and then compensate for the increased height by zooming in using the remote controller’s thumb wheel.

9

I would recommend a different approach. I would leave the height lower (no zoom), increase z-check so that waypoint are only at the boundaries of the mission (if the area is relatively uniform), and reduce the overlap to something around 50% or lower. If you are just starting out with mapping use those setting then adjust as necessary.

1 Like
10

I had to re-read this mention of leaving waypoints at the boundaries before I realized that this advice to eliminate superfluous waypoints conforms with Sam_G’s waypoint deletion idea that can be used to keep the waypoint count below 99 on mapping flights…

Hearing that the Mavic 2 Zoom would best be flown at a low enough altitude where the zoom feature won’t be needed also stands to reason, considering that zooming in will narrow the field of view, thereby reducing the percentage overlap of the images generated.

With a light seasonal drizzle outside today, I’ll take a leisurely approach to experimenting with variations in altitude and judicious waypoint deletion before the skies clear up in the next couple of days.