It seems that both Motion Based and SportTraks have a means of cross-referencing GPS track-points with elevation survey data. Finlay kindly provided me with the SportTraks data for a sample of races on my ranking table for comparison. Initially I was sceptical about the ST data, because it was counting quite significant undulations as 'flat', but Finlay has managed to fix this problem now.
As a result, I now think that the ST output might be worth considering as a longer term alternative way of generating my Hill-ranking table. Some more analysis is still required, but given that future of the MB Gravity Web service is in doubt, ST may be a useful back-up plan. Unfortunately it would require myself and Finlay to re-process another 80-odd races!
The cleaned ascent/descent data from ST and MB produce quite different hill-rank scores, but the relationship between the scores of different races remains similar as does the ranking order. It is the relationship between the scores of different races that is important to make meaningful comparisons in any case.
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