To prepare a plot, I first select the shape to draw in the sand. I chose the DXF format as it is wide spread and it contains vectors. Later I can use another format.
I then use an C# application to transform vectors in GPS coordinates. Just choose the scale, place the mouse on a map and just click.
To be verified, coordinates are exported to a KML file that can be imported into Google maps. Pablo uses another file with more information to trace the shapes in the sand eg to raise and lower a tool like
48,4450406781251 -2,08504594716869 False
48,4450461265302 -2,08506101814332 True
48,4450517909435 -2,08506631507817 True
48,4450666555887 -2,08506418650572 True
48,4451036193834 -2,08505440264829 True
48,4451291246728 -2,08504492712652 True
48,4451318136836 -2,08504202502935 True
48,445129096546 -2,08503937794103 True
48,4451265609555 -2,08503508080721 True
48,4451263169431 -2,08502652944985 True
This video describe the process :
Pablo can be brought close to the fields, he must continue alone. The serious work can begin !