-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Andy Allan wrote: > On Mon, Sep 15, 2008 at 11:08 PM, David Earl <[EMAIL PROTECTED]> wrote: >> On 15/09/2008 22:07, Donald Allwright wrote: >>> The theory is that >>> if the SRTM data include an altitude reading for the lake itself (I >>> haven't actually checked this yet!), I should be able to use an approach >>> similar to what you suggest to get a much more accurate map. The holy >>> grail would be to be able to click somewhere within a lake, and the >>> software to automatically generate a perimeter. However I suspect that >>> will be a long way off, if it ever happens. >> But will the accuracy be any better? SRTM seems to be 3 arc seconds >> outside the USA = approx 90m of latitude per pixel. > > Absolutely. I can see the idea, but if there's Yahoo or even Landsat > imagery it'll most likely be more accurate that way to get lakes. > > And don't be fooled by the contours on the cycle map - they might be > thin and look really accurate, but they are just massive > extrapolations from relatively low-resolution DEMs. Most lakes have > one or two contours running underneath them at the moment, some rivers > run uphill in some places (especially in narrow gorges) and so on. > > Cheers, > Andy > > _________
Absolutely agree - I live near the hill in Essex (OK, there's 2..) & SRTM has it quite badly wrong, both height & just where the highest point is - by around a mile. Any lakes generated from that would be, well, unpredictable! Given how flat the surrounding area is I found that quite disappointing. Mark -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFIz6dMJfMmcSPNh94RAnZhAJ0X7zWZcuixPAdDRfUAyw/GqdyudQCfbIAz +Y2r5ph9gROK+UN5+Ea4Fq0= =HdNV -----END PGP SIGNATURE----- _______________________________________________ talk mailing list [email protected] http://lists.openstreetmap.org/listinfo/talk
