Lotrechtes Obholz = HAP = Height Above Plate
Rechtwinkliges Obholz = What we would call the structural engineering D4 calculation.
Sparrenhöhe = depth of rafter
Lotrechte Kerventiefe = Height Below Plate
Lotrechte Sparrenhöhe = Rafter Plumb Height
Dachneigung = Rafter slope Angle
The standard American rafter seat calculations starts with the length of the seat cut or HAP of the rafter. The Germans and Europeans use the Rechtwinkliges Obholz method. A dimension parallel to the top of the rafter.