john_tullamarine,
I should have been more specific. My programmes do the conventional calculations for discrete obstacles, but also include STOD/OCG input for Australian operators wishing to use STODs as core data (Survey limits longitudinally and laterally require considerable additional discrete obstacle data). Their desire to use STODs as 'core' data emanates from a wish to respond quickly to NOTAM changes.
The problem does not lie in the 2nd segment, but in the 1st segment. (This is the incompatability of STODs with AFM data that I alluded to). As it's impossible to know from a STOD just where the obstacle is (dummy or real), I ensure in the programme, that the 1st segment lies above the TODA and the Obstacle Clearance Plane.This requires the programme to do a bit of trigonometrical manipulation considering 1st Segment Gradient and Length, End of TODA Slope, and published STOD Gradient, to find the reduction in STOD necessary to achieve this. The end result is that screen height is achieved a few hundred metres before end of TODA, 1st segment then continues above the remaining TODA towards intersection with the STOD OCP beyond the TODA. Obviously a bit conservative, yielding a typical screen height of 44 feet (9 feet in the bank), but the best means that I consider for handling 1st segment when using STOD data. (STODs in this context include TODA and it's associated OCG).
If things start looking too conservative, then back we go to Type 'A' runway charts and full discrete obstacle analysis, the STODs go in the bin.
Regards,
Old Smokey