I am an engineer.  I asked my client’s lawyer a while back when I was doing some work for them.  

The lawyer told me the actual IL law is that engineers and surveyors can’t be charged with trespass if they need to access adjoining land for a professional purpose.  They can be held liable for actual damages if they wreck things, especially intentionally.  Like driving a UTV around in someone else’s crop instead of doing a topo survey on foot.

I usually ask permission/inform the adjoining landowner if it’s convenient.