For straight driving and control of tractors and machines Gebr. Ezendam BV in Borne (the Netherlands) supplies various GPS systems from the Trimble brand.
We have already completed several projects successfully among others fertilizing with a Vervaet and drilling plant holes with GPS all this at 2 cm accuracy. Soon pictures and videos of these projects will follow until then you can link to our supplier of GPS systems Agrometius. Should you have any questions you can always contact us.
You can find more information about the GPS on our Dutch website.