A Review of the DJI GS Pro App: Part 2

In the first comprehensive review and field test of the DJI’s new waypoint and mapping app – DJI GS Pro – I covered the app’s features and functions in detail. In this post, I outline my experience field testing the app with my Phantom 4, and include real-world sample orthomosaics and 3D models for you to compare.

So how does the new DJI GS Pro app perform in the field? Well, generally not too bad. I conducted two map tests over an area near where I live: one relatively large map of a whole village, at almost 9 hectares in size (something that would require more than one battery to complete), and one small map to compare how 3D models look captured with different settings.

The app is not perfect by any means. It suffered a number of glitches and anomalies during testing, and there are a couple of glaring omissions that become apparent once you start using it. But to be honest, none of the other third party mapping apps are that great either. Overall, this is perhaps the most comprehensive, full-featured mapping app for DJI aircraft to appear so far.

Because its a DJI app, you get the feeling the developers were able to gain access to DJI aircraft code and tech that perhaps isn’t currently available to third party developers. You can see that in the telemetry and data you get back from your aircraft, once connected to the app. Plus, there are also clearly elements that have been carried over from the (now very mature) DJI GO app.

So how does it perform? Let’s start with a larger map.

Note: these tests were conducted with DJI GS Pro v1.0.0. At the time of writing, the app has been updated to 1.0.2, which may have fixed some of the issues I encountered. And all these maps and models were uploaded and processed on MapsMadeEasy. All process settings were the same for each map.

Village Map

For this exercise, I decided to map the village where I live here in the NT. I conducted two missions to generate two maps: one at a 60m (197ft) altitude, producing an image resolution of 2.6 cm/pixel, and one at 40m (131ft) altitude, producing a 1.7 cm/pixel resolution.

Both maps had the following settings:

  • Camera Model – obviously, this was Phantom 4
  • Shooting Angle – parallel to main path
  • Capture Mode – Capture at Equal Dist. Interval (I couldn’t get Capture at Equal Time Interval to work – the app popped up a warning saying this mode was not compatible with the Phantom 4. This may have been fixed in the recent update)
  • Flight Course Mode – Inside Mode
  • Speed – this was 2.6 m/s at 40m altitude, and 3.09 m/s at 60m altitude. If you use either ‘Capture at Equal Dist. Interval’ or ‘Capture at Equal Time Interval’ the speed slider is optimised and set automatically, depending on the altitude set. It can’t be adjusted independently. If you select ‘Hover&Capture at Point’, then the speed can be set independently of the altitude.
  • Front Overlap Ratio – 90 percent
  • Side Overlap Ratio – 70 percent
  • Course Angle – 0 degrees
  • Margin – 0
  • Gimbal Pitch Angle – 90 degrees

Obviously, the 40m altitude produced a lot more waypoints and legs that needed to be flown. GS Pro calculated the following for each map:

  • 60 metres: 
    • Flight Time – 19min 27sec
    • Flight length – 3,601 metres
    • Number of Waypoints – 26
  • 40 metres:
    • Flight Time – 42min 28sec
    • Flight Length – 5,188 metres
    • Number of Waypoints – 38

One thing missing: there are no options in the GS Pro app for any type of camera setting. There is nothing in the way of camera control at all: for that, you have to go into the DJI GO app and adjust all your settings there first – and manual settings at that – then go back into the GS Pro app. This is somewhat of an inconvenience.

And I also noticed a weird anomaly after using the GS Pro app and returning to the DJI GO app. On entering the GO app again, I found that the photo take interval was always set to ‘Timed Shot’ and not single shot (or any other setting for that matter) – odd!

Also, adjusting some of the slider settings for altitude, overlap, etc is very fiddly. The sliders are very sensitive, and there’s no option to tap the text box and just enter a value – values have to be set with the sliders. Another annoyance I hope they can fix in a future update.

60m Flight

The telemetry panel during flight, showing the useless and inaccurate photo count.

The first mission conducted was the map at 60m altitude. This was just about completed on one P4 battery, and generally went off without a hitch.

One thing I noticed right away while the mission was in progress was the telemetry panel, lower left of the interface. This provides useful information about speed, position (in Lat and Long coordinates), and altitude.

It also provides a running count of each photo as its taken, but it quickly became apparent that this count couldn’t keep up, or was seriously flawed. The photo count would go for a while, with a flash of the image thumbnail, plus a reassuring shutter ‘click’ sound, but it would then inexplicably stop. Not until the aircraft reached the end of a leg, or arrive at a waypoint, would the count start up again.

After the flight, I checked the number of photos actually taken and on the SD card against this photo count readout, and it was hopelessly out. It appears the app carries on taking photos at the preset regular intervals, but the feedback in the panel during flight is just not keeping up. Its really not much help like this, and doesn’t inspire confidence that photos are being missed out on some of the waypoint paths.

Village Map, 60m:


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Village 3D Model, 60m:


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40m Flight

On the second mission, to capture the village at an altitude of 40m, things didn’t go quite so well. Half way through the first leg (on the first battery), the app crashed. The aircraft kept going, but on restarting the app, it couldn’t connect to the aircraft, which continued with its mission. But without any feedback from the GS Pro app, it was hard to tell whether it was carrying on as normal, and continuing to take photographs, or just drifting off into the distance.

So I initiated a Return-To-Home and the aircraft came back without incident. Taking a quick look at the photos on the SD card, it appeared as if the aircraft had continued to take photos after the app  had crashed, but given that the app had crashed, and therefore had no record of the last point captured before RTH was initiated, I scrapped that mission, and inserted a fresh SD card.

To be fair, I’ve had most the third party apps crash on me at one point or another on larger, multi-battery missions, losing connection while the aircraft carries on its mission. Map Pilot has done this on more than one occasion. Sometimes, you’re able to reconnect, but sometimes not.

Starting the 40m mission again with a fresh SD card, this time things went slightly better. My usual 30 percent battery warning sounded as normal, and I was able to initiate Return-To-Home by pressing the Pause button in the GS Pro app. A small menu pops down and you can select ‘Pause Mission’ or ‘End Mission’. Pause mission allows you to return to home to swap out the battery.

So I did: the P4 came back fine. I swapped to a fresh battery, started her up and tapped the Airplane icon. here you can select resume mission, and the ‘Prepare for Flight’ dialogue pops up. Tap ‘Start to Fly’ and the aircraft takes off and heads to the last point in the map where it left off.

Two more annoying things here:

  1. The P4 flies out to its resume point (or start point, if this is the beginning of a mission) very slowly. It basically flies out at the speed that’s set in the mission parameters. So, in this case, for a ‘Capture at Equal Distance’ setting, at 40m altitude, the aircraft will fly at 2.6 m/s during mapping. But it also flies out to the start/resume point at 2.6 m/s! Far too slow, and a waste of battery juice! It should be getting out to the start/resume point a LOT quicker than this.
  2. I noticed on a couple of occasions, when I paused a mission half way down a mapping leg, the aircraft would not resume the mission from that same point half way down a mapping leg. It would resume the mission from the next nearest waypoint at the END of the leg! So basically, the app would not capture any more photos for the rest of that leg. This is an annoying oversight that can really effect the quality of your final map. For now, the workaround is to pause and initiate RTH a mission at the end of a leg, on or as close to a map waypoint as possible.

Village Map, 40m:


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Village 3D Model, 40m:


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NT House

I also flew two smaller missions over a house near the beach here, to test the difference between the ‘Capture at Equal Dist. Interval’ mode and the ‘Hover&Capture at Point’ mode. Both flights were flown at 50m, producing an image resolution of 2.4 cm/pixel.

While there was no discernible difference in the image quality of each of the maps, there was a SIGNIFICANT difference in terms of accuracy of fit on the underlying map, and in terms of the 3D rendered model. As you’ll see below, the sides of the house and other structures in the ‘Hover&Capture’ 3D model are rendered significantly better than those in the ‘Capture at Equal Dist.’ model.

I suspect the ‘Hover&Capture’ mode seems to be producing better results because;

  1. the aircraft is stationary at the time of image capture, and because of this, the GPS coordinates tagged with the image are more accurate and precise. If the aircraft is moving as the image is taken, the GPS coordinates get written to the image (tagged to the file) a fraction of a second after the image was taken, by which time the aircraft has moved on from the actual position when the image was captured. No matter how small that gap is, it can lead to a position inaccuracy of a couple of metres. In the ‘Hover&Capture’ map, you can see that – while the fit is not perfect – the map is much more accurately positioned on the underlying satellite image than the ‘Capture at Equal Dist.’ map.
  2. again, because the aircraft is stationary when the photo is taken, even straight down at 90 degrees, its capturing better image data, enabling better rendering in the 3D model, particularly of vertical surfaces. It’s almost as if images captured while the aircraft is constantly moving are adding a degree of “rolling shutter” effect to vertical rendered surfaces, even though I was using a pretty fast shutter speed (well over 1/800 sec) and this was a bright day. The motion of the aircraft while an image is being taken seems to introduce a degree of distortion that’s not present in the Hover&Capture images.

3D House Model, Capture at Equal Distance Mode:


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3D House Model, Hover&Capture Mode:


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Log Files

In short, there are none.

You’d think, given that this is a DJI app, you could enter your DJI account details, and the app would be able to sync logs and flight data over the cloud, just like the DJI GO app. But no, there’s none of that.

No sign of the GS Pro app in the iTunes File Sharing panel, so it would seem no log or data files.

In fact, there doesn’t seem to be any saved or recorded log files at all. Plug you iPad into iTunes and scroll down to the File Sharing panel, and GS Pro is not even listed. The GO app is there, the GO 4 app is there (if you have it), but no sign of the GS Pro app.

This is a serious omission, because it means that for now, you’re stuck with having to manually log each mission. I hope this can be addressed in a future update.

Conclusion

Despite its shortcomings, the DJI GS Pro app is a worthwhile addition to orthomosaic mapping sector, and on the whole does a very good job. The ability to create and save missions in a consistent and easy-to-use interface, its strong communication links and telemetry feedback with DJI aircraft (crashes notwithstanding), and excellent Hover&Capture flight mode make this a worthy contender in the mapping landscape.

Issues that need to be addressed are mission resumption from the same point on the map, some indication of the area to be mapped (in hectares or acres), better and more reliable photo count tracking, less fiddly slider controls with an enter-value option, and adding of log files and data.

We also wait to see how the POI feature will add to the quality of 3D models created from the app. Right now, calling the mapping function in the app a ‘3DMap’ is a bit of a misnomer.

A good start, but there’s work to do.

Nick Foxall
February 2017

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