In the real world...
First of all, I'm continuing this dialog in the spirit that you're interested in other points of view and learning more, not in making a point. Your statements so far I think show that.
Respectfully, I think you've missed the point I was trying to make, and that might be because I didn't make it well enough. I was simply and only saying that that the chart will not give you the margin of error
. Those three words are my focus. Countours or no, an IFR chart does not have that kind of data and that kind of precision. Pilots don't care what the margin is anyway, and most instrument pilots don't even know. Nor are they required to, at least in the US. The design of the procedure takes all that into account. "Fly it right and you're at a safe height." That might be hard to grasp, but operationally, it works just fine. In your example, it might be possible to approximate your height above terrain, but it's irrelevant operationally. I'm not saying it can't be done, only that it will be an approximation and of no use.
Here's an example. In the US, flight at or above the minimum enroute altitude on an airway guarantees at least 1,000 feet above the highest obstacle within 4 nautical miles of course centerline in non-mountainous terrain. It's actually a bit more due to rounding things up, but let's keep it simple. In mountainous terrain, it's 2,000 feet. Knowing your exact postion on the airway, and comparing it to a visual navigation chart (which has detailed contours) could allow you to determine you were exactly 2,201 feet above a given mountain and therefore 201 feet above the guaranteed minimum. Whether you have an extra margin of 201 feet or the bare minimum doesn't matter. What does is that under the most adverse conditions of pressure and temperature error in your altimeter, course guidance, turbulance and imprecise flying, you're still safely above the rocks. You don't care how much, you just care that you are.
Maybe a little detail will help. I happen to work with a group of guys that are responsible for designing special instrument approaches into places that don't quite fit the standards. To design the approach and missed approach paths, they apply the obstacle clearance criteria (much more info can be found here
) against highly detailed charts called obstacle clearance charts. These are tabletop sized documents that map out carefully surveyed points and are only of use for designing the procedures. The product of their work is a text based document that a commercial chart provider can use to produce a chart. They simply transform climb or descent gradients at expected values, courses, turns at expected radii and so forth to produce a visual product. The only indication of how high you are above the ground or touchdown zone on the runway (depending on the procedure) is at the missed approach point. The chart makes it much easier to fly of course, but it doesn't document the margin of error
If you want to learn what the margin is, the document in the link will tell you.
To summarize what I've been trying to say, knowing where the rocks are is irrelevant. Follow the procedure and you have guaranteed margin. Stray off the path and a chart won't help you.
As an aside, how did you get the text into the little boxes you can toggle on and off? Really saves the screen real estate. Nice touch.