Fix README

README.md

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+## Why?
+
+QGroundControl is great! It's open source and provides the ability to easily
+produce "survey" flight paths, which often costs a lot of money to achieve
+via other apps and software.
+
+Unfortunately it does not work with DJI drones.
+Some great looking work has been done with https://github.com/diux-dev/rosettadrone
+which seems to provide this capacity.
+I have not tested it, but looks cool.
+
+For one reason or another, I decided to just use the flight plan output from
+QGroundControl and wrangle it into a shape that DJI GO 4 is happy with.
+This way I can use the stock DJI app for now, until I have tested, and am
+comfortable that the `rosettadrone` approach is stable for my uses.
+
+And I get to save masses of time with survey-type waypoints :D
+
+
+## Description
+
+Convert QGroundControl survey waypoints to DJI GO 4 waypoints 2.0.
+This is spefically intended to work _only_ with the "survey" mode from
+QGroundControl.
+
+This will likely only work if your smartphone is rooted, as you will need `su`.
+My personal recommendation is to get `Magisk` installed.
+
+This script is largely very naiive. It works as expected with `qgroundcontrol
+v4.0.11-1` and `DJI GO 4 v??` as of date 06-11-2020.
+
+There is no guarantee it will continue to work with future updates of either
+application. You have been warned.
+
+By default, a backup of the original DJI GO 4 database is made, so even if
+the resulting db is broken, you can always recover the original.
+
+Has only been tested using `omnirom beryllium` - your mileage may vary.
+
+
+## Dependencies
+
+For the script:
+- Python 3
+  - all required modules are I believe part of python core
+- sqlite3
+
+Obviously:
+- QGroundControl
+- DJI GO 4
+
+
+## Prerequisite
+
+- Open QGroundControl
+  - either with the app on your phone, or more easily with the
+desktop version. Tested with Linux and the App, but should be the same for Mac
+and Windoze
+- Create a survey waypoint mission
+- Make sure the camera lens settings are all correct
+- Use your common sense to determine
+  - suitable overlap
+  - cruising flight speed
+  - suitable altitude
+  - other?
+
+Some settings can be passed directly to the script from the commandline, and
+will overwrite the equivalent values from QGroundControl.
+
+*n.b.* This script currently ignores takeoff and landing points, and solely focusses
+on the survey mission waypoints, at a single altitude.
+
+
+## Preparation
+
+It is assumed that you have a terminal open on your "host" in a suitable working
+directory, and that `qgc2dji.py` is in that directory.
+When copying the `.db` you can store it wherever you like - it just has to be a
+location that `adb pull` can retrieve from.
+Once your phone is rooted and reasonably under your own control (developer
+options enabled, USB debugging enabled):
+
+
+## Usage
+
+Use your own judgement when it comes to `chown` and `chmod` to match the original
+`.db`
+
+```
+[host]$ adb shell
+
+[phone]$ su
+[phone]# cp /data/data/dji.go.v4/databases/way_point_2.db /sdcard/
+[phone]# <ctrl-d>
+[phone]$ <ctrl-d>
+
+[host]$ adb pull /sdcard/way_point_2.db ./
+[host]$ python ./qgc2dji.py -i <qgroundcontrol savefile> -d ./way_point_2.db
+[host]$ adb push ./way_point_2.db /sdcard/
+[host]$ adb shell
+
+[phone]$ su
+[phone]# cd /data/data/dji.go.v4/databases
+[phone]# mv /sdcard/way_point_2.db ./
+[phone]# ls -ld
+drwxrwx--x 2 <user> <group> 4096 2020-11-06 11:48 .
+
+[phone]# chown <user>:<group> ./way_point_2.db
+[phone]# chmod 660 ./way_point_2.db
+```
+
+
+## Future
+
+- Also update 'way_point_2_cache.db'
+- Choice of "action upon mission completion"
+  - Currently defaults to hover
+- Altitude per waypoint
+- Takeoff and landing points?
+- Calculate appropriate crusing flight speed?
+  - Dependent on required overlap and limitation of camera regarding photo
+    interval
+- Waypoint triggers (start/stop recording, take photo, etc)