Like last year I plan to have a walk in Albania during my holidays.¹ The planned route is this.
Though the mobile phones I use are Siemens ME45 I already had had contact with Peter Neubauer from Mapillary now and then and also heard him on Radio OSM (German OSM podcast #31). So I asked him about recommended hardware to run the Mapillary app for some days far away from civilisation and power sources and to store away the lots of images created.
In walking mode the Mapillary app is set to make a picture every two seconds as default AFAIK. After having had a first walk with Mapillary this seems to be a reasonable choice. Since my average day trip lasts up to eight hours and I assumedly will hike on 18 days I calculated the following:
pictures/minute x 60 minutes x 8 hours x 18 days x picture size 5 MB = assumed amount of created data
30 x 60 x 8 x 18 x 5 = 1.296.000 MB
After some mail exchange he sent me in the name of Mapillary the stuff we assumed would be best. Aside from the mounts mentioned in the other blog post I purchased an Y-OTG cable which allows USB drives to be powered from an external source while connected to the smartphone as host. Although there are dedicated backup devices – a HDD with battery and card reader attached² – we skipped purchasing such a device because it would have cost additional 250 EUR.
A list of the hardware:
- 2x 128 GB microSD card
- 1x magnet charging cable
- 2x deltaco Powerbank 10 Ah
- 2x short cables USB-A–µUSB- ~20 cm
- 1x long cable USB-A–µUSB- ~100 cm
- 1x µSD card reader für USB
- 1x 8 GB-µSD-card (assumedly forgotten in the reader)
- 1x OTG cable µUSB–USB-A-Buchse
- 1x Sony Xperia Z1 Compact (w/o SIM-card)
- 1x external 2,5" USB 3.0 drive 2TB
And two things I won't take with me
- 1x Speedport miniature 4xUSB-Hub
- 1x power adapter for the above
Last weekend I had everything ready to make a test under real conditions. The app was set to use continous autofocus and stable shot.
The following I could observe:
Running Mapillary about one hour discharged the battery by 30% and the phone got quite warm.
(I already had disabled/uninstalled a lot of needless stuff and installed BlackouT to dim the screen as far as possible to save energy)
Although I had walked for two hours Mapillary "only" made 1118 photographs needing 5220 MB of space. 30 images/minute in two hours would theoretically have resulted in 3600 images.
Speculations on the number of images:
Although the camera is a good one for smart phones with a 1/2,3'' ccd it in total numbers the lens is not fast. This results in low shutter speeds in shady environments and relative high noise.
When I walk through a dense wood, for one I am moving and this in a dimly lit environment. Although the camera is mounted near the shoulder where it is not moved too much the app still has to wait for moments where the movement is small enough to make pictures not blurred by movement. example sequence at mapillary
I'd also assume that the camera has problems focusing in low light.
I think these two points are the main reason that the number of recorded images is only one third of the images the app should have recorded theoretically.
Maybe one should also consider to mount the camera at the shoulder strap a little more to the sternum and away from the arm since it seems I lifted it a little with the arm sometimes.
Now for the quality of the images: As explained above the phones camera doesn't perform too well in shady environments.
I had not expected the number of defocused images I got (example). I assume this was mostly caused by me using trekking poles which I assume irritated the camera (you see them in some of the images). Since the continous autofocus also consumes some energy I disabled it which sets the camera to fixed infinity focus. So far I only could do a small walk with this setting and without poles but at least the pictures aren't worse.
Copying the remaining 4,4 GB of good images to the external drive took about five minutes. For testing purposes I had copied 32 GB of files sized ~50-100 MB from µSD (in the smartphone) to hdd which took 20 minutes.
It seems I cannot test how often I can charge the phone with one of the 10 Ah battery packs – I will see during holidays. The long cable mentioned in the list is for charging the phone while walking. This I also have not tested but I don't think there will be problems.
For now I thank Peter Neubauer and Mapillary that they allow me to add another 1,2 kg electronics to my luggage, to shoot (and later host) tons of images during my hiking trip – and most notably the confidence that they borrow me all the stuff.
¹ German blog post linking to some reports
¹ English description of hike at wikiloc
² Two not insanely expensive devices with 1TB are this and this
There is also the possibility to combine a barebone device with a HDD of the own choice, maybe with the additional battery for better being safe than sorry.