I would like to add AB-lines manually in the .txt file, but I fear there is no quick way to do this. The challenges:
1) A way to convert a (lon, lat) point to the local (x,y) used in AgOpenGPS
2) Heading of a line in QGIS (projection EPSG, WSG84, ...) equivalence to the heading in AgOpenGPS, or a way to convert it.
Would this be correct?
For who it may have worth, here is a way I found to get coordinates into a KML which can then be loaded as a field boundary. For example if you have done a Reach or other RTK survey of a field and want to get this into AOG. Basically I edited a KML that worked, feel free to improve and/or add to the wiki.
1) load the coordinates from CSV or from the attribute list of the shapefile into a spreadsheet
2) combine longitude, latitude and ",0" with a text joining function & or CONCAT. In a new column you get for example a cell with content "11.11111111,22.2222222,0".
2) open a new .txt file in notepad, paste the following and paste your new column under <coordinates>:
<?xml version="1.0" encoding="UTF-8"?>
lon.decimal,lat.decimal,0 lon.decimal,lat.decimal,0 ...
3) replace enters between coordinates by spaces
4) save file and rename .txt to .kml, open as field boundary in AOG
5) see your boundary and hope this is a good way to do this