[Closed] Syfydrin Trail Nant Yr Arian - dont believe the height gain on the offical map

Wonder if it was worked out by the same person who did the height gain on the Marin Trail - because that's a barefaced lie too.

At least NyA is a cracking ride though.

GPS is a pretty inaccurate way to measure altitude. If you're 50% out and they are too, it might not be all that bad.

Scienceofficer, is that really true? And does that go for both the pressure and mapp calculated height gain? I might go and measure more accurately in Memory Map.

Experience says that 1,000m is more likely though

Yep, great ride, especially if you want to show a newbie a bit of everything (apart from a pub!)

Yes. Don't rely on memory map either. In mapping circles, its well known that OS were pretty good laterally, but aren't very accurate vertically. Their trigs haven't been maintained since 1974.

Pressure is, I understand, the best way, once its been corrected for weather, in addition to satellite radar which is the daddy-mack.

Init?

😕

Just checked when we did it last year and I got 1138m on a Garmin 60Csx

i did this last week and was looking on an OS map afterwards to get an idea of the route we'd done - i reckon the contours on the last climb alone show a climb from about 100m to 430m or thereabouts, so that would back up your findings. good fun though 🙂

From the map I think you are 30m out at the bottom and 50m out at the top there, theflatboy (having checked multimap where I can enlarge it)
And what's this about OS not being accurate vertically? Do the trig points move up and down or something?
I ride the route regularly and I was thinking that the stated 670M sounded much more reasonable than these 1000M+ estimates - but then I have nothing to go on other than my experience based on OS data and no idea how I'd check it. Agree on the good fun bit though.

you might be right there nos - the contours are so close together around there i found it hard to make it out! and i'm taking that climb right round to the top, after you've rejoined the other routes right to going back into the woods at the top.

I would say its in the just over 1000 meters area as on nearly every ride we have done of the Syfydrin Trail someone in the group has a gps unit and they have all given readings within 20 meters of each other.

Perhaps they are all equally wrong? But my GPS (uses both pressure & sat's) has read 776,777 & 776 the three times I have taken it to the trig point on the top of Drum Mt which is 777 meters according to the OS maps. I do tend to calibrate the unit at the start point which is also a known height.
According to the same site the Beast @ Coed Y Brenin is only just over 1000 meters!!!

Actually, they do move up and down, although only by a small amount.

Its more to do with the source survey data I understand.

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What ScienceOfficer said:

GPS is only a vague guide to altitude. It's because of the difference in angles between your plane and the satellites is small i.e. they are all above you, so triangulation is poor. If the Earth was transparent your unit could "see" the satellite below you as well. The triangulation would be good and height as accurate as lat/long. If your unit is using pressure as well, then it's much more likely to be accurate, assuming you calibrated it at a "known" height [this is how mountaineers judge if they have climbed the right summit when in cloud]

Actually, you go up and down a lot more than maps suggest because the "bumps" you ride over are "flats" between contours on the map. Similarly, you ride further than maps suggest because the distance over all those gradients is greater than the "flat" distance on the map [I'm simplifying here, I know that Mercator-type projections used in OS maps distort distances in order to preserve angles for compass work]

Still, comparing 670m climbed with >1000m climbed suggests that the trail people got it badly wrong.

chunkypaul - Member
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