I don't have a calculator with me to work out the result/s, but..........
If there was only one limiting obstacle (rare), YES, you may by simple geometry calculate the exact height and distance of that one obstacle.
The problem with Australian RDS data, you don't know how many limiting obstacles there are, and, in fact, each of the gradients published may have "their own" obstacle, but all is not lost. By calculating the intersection of each successive STOD or TODA gradient, you may construct a SERIES of intersections, thus creating an Obstacle Polygon, where the intersections are actually "phoney" obstacles, but SAFELY above all REAL obstacles. So there, now you have a series of obstacles to play with.
One very important final consideration in constructing an Obstacle Polygon is that for all Obstacle Clear Gradients published ABOVE the lowest (1.6%), all obstacles will now be considered EXCEPT for a possible more distant obstacle generating the lowest published OCG (1.6%). In this case, you will need to pull out the survey Charts to find a POSSIBLE obstacle which may be generating the 1.6% OCG.
Advice of the Runway Slope would be beneficial, as the OCGs emanate from the runway surface, which, for a sloping Runway, be originating from a different elevation.
J_T, did I learn well from the master?
Regards,
Old Smokey