Based on my search, there is no commonly available, widely recognized, or official software, tool, or document formally named "gnacad" with a readily available "gnacad tutorial pdf".
that provides specific measurements and schematics for practicing precise drafting. GnaCAD Floor Plan Activity Guide : A comprehensive Scribd PDF gnacad tutorial pdf
Before diving into the tutorial, we must understand the "why." Every GNSS antenna has a physical center (the metal base) and an electrical center (where signals are received). These can differ by millimeters. Over a 10-hour observation period, uncorrected phase center variations can introduce centimeter-level errors—a disaster for deformation monitoring or cadastral surveying. Based on my search, there is no commonly
gnacad -antex igs20.atx -plot TRM59800.00 -gnuplot