Getting the geometry correct is vital to the install.
Cardboard is the key for making a template up on site,
Make a template of the A,B,C points, Post and hinge points
From this you can pencil everything to give you any custom bracket requirements.
Back to the workshop for a few hours to get them made up and colour coded.
I personally do all our gate geometry measurements and templates this way
We used to have a good mobile fabricator, but he retired. Now I do all our own
Skilled and competent designers and installers are hard to find these days