27. December 2014
So, by now some of you have opened a holiday gift and it turned out to be a drone. I was fortunate enough this year to get a 3DR IRIS+ in my stocking. After a few flights I wanted to put together a quick note comparing this with another popular consumer drone, the DJI Phantom 2 Vision+ (P2V+). I have a P2V+ that I use at work and put quite a bit of thought into what I would get for personal use. Hopefully this will be of use to readers who may be considering the purchase of a drone this year. Allow me to begin by saying that both are great products and work well for hobby or possibly commercial work (if you live outside the U.S. 🙁 ).
A drone at home
My interest in drones primarily revolves around mapping applications using low-cost cameras and structure from motion algorithms. Drones have a great future in a variety of small-scale mapping applications, including hazard mapping, precision agriculture, long-scale geographic and geological monitoring. Or, just mapping the area around your house, which is what I’ve been doing lately.
Which drone is right for you?
The big question for me (and the point of this article) was which drone did I want to get? The first thing I did was lay out what features were important for me.
|Feature||3DR IRIS+||DJI Phantom 2 Vision+|
|Easy to Fly||Yes||Yes|
|Programmed Flight Mode||Yes||Developing|
|Camera/gimbal capable||Yes, with separate gimbal and GoPro||Integrated gimbal/camera|
|Flight time||16 minutes with gimbal||20-22 minutes|
|Battery cost||US$40 per battery||US$150 per battery|
|First Person View (FPV)||Add-on with goggles or screen||Integrated with iPhone or Android phone|
|Easy to build||Yes||Yes|
|Return to Launch (RTL) if loses radio contact||Yes||Yes|
|Other payloads||Yes, easy gimbal removal||Harder to remove gimbal|
I’m sure people might argue, but these are based on my experience and what I considered to be important. In the end my decision came down to a few primary factors, which are bolded in the table.
To map small areas it is very important to be able to fly pre-programmed, structured routes. The IRIS+ accomplishes this through the full-featured APM Planner or Droid Planner software. It seems to work well and is easy to program routes. DJI is developing this capability for the P2V+ through its mobile app. In my experience it does not work as well as I would like and I don’t trust it yet for flying automated routes with the P2V+.
For data processing, I like to start with geotagged photos. The IRIS+ was a clear winner here. With GPS logging at 5Hz and easy access to the logs I am able to geotag my images easily using exiftool (A future article will go through this workflow). The DJI logs GPS data very slowly and does not provide access to the logs. Geotagging requires the use of another instrument, such as an iGotU-120.
This is a good place to note that the IRIS+ logs much more than just GPS. You can pretty much log anything about the drone that you want. I haven’t had a chance to work too much with logging yet, but it certainly brings out the nerd in me.
I really have to give it to DJI here. They get every bit of flight time that they can out of a battery. I can regularly get 22 minutes from the DJI at upwards of 100m altitude. The best I have done with the IRIS+ so far is about 15 or 16 minutes. While 5 or 6 minutes doesn’t sound like a lot, it is 35% of the IRIS+ total flight time, and can make a big difference in what type of data collection profile you can fly.
Of course, one way to trade off flight time is with cheap batteries. The DJI batteries run about US$150 per battery, while the IRIS+ uses a standard 5100mAhr 3S battery. Instead of extra flight time, I just pack a couple extra batteries. Time will tell whose batteries are more reliable and hold a charge better.
You might wonder why I didn’t put camera quality higher on my list? Both units match up pretty nicely in this regard. For the IRIS+ you need to supply your own GoPro or similar camera, while on the P2V+ you get the integrated camera and gimbal. Neither of these cameras are optimal for photogrammetry purposes, they are pretty similar in overall characteristics and quality. I’m hoping to get a better frame camera to fly on the IRIS+, but haven’t tried it yet.
First Look Orthoimage
Initial results so far with the IRIS+ have been great. It’s pretty cold and dark where I live so hard to be mapping much. After a bit of experimentation with the GPS logs, I was able to geotag images from my GoPro Hero3 and generate the orthoimage below using AgiSoft Photoscan. Accuracy with only image geotags is around 2 meters. Can’t wait to see what can be done once summer comes around.