On Mon, Dec 15, 2008 at 1:45 AM, Olly Betts <olly at survex.com> wrote: > I don't think inventing numbered grades here is a good approach. For > centre-line survey data, a grade summarising how it was collected makes > sense as you're trying to summarise the accuracy of a lot of > measurements at once, and there's no direct indication of individual > errors for particular readings. It also gives people a benchmark to aim > for, which can be tested by analysing loop misclosures.
The reason why we started to think about position measurement grades is that we are collecting data about hundreds of caves and other karst features in our area. In the summary tables (export cave-list) we need some indication of precision of entrance location (e.g. to select entrances the position of which needs to be refined). So some standardization seems to be necessary. Naturally the SD setting would be available for measurements with known error estimates. > Also, the suggested grades force particular pairings of horizontal and > vertical errors. Just because a "GIS GPS" might be 1m/3m, that doesn't > mean that every alternative technique for surveying to 1m horizontal > accuracy would give 3m vertical accuracy. There is the same problem in centreline data (different combinations of compass/clino/distance accuracies) with just one generic grade to keep things simple. Perhaps the standard positioning grades need not to distinguish between horizontal and vertical accuracies and user should use SD setting for fine-tuning? Martin
