[TowerTalk] TowerTalk Digest, Vol 104, Issue 42

[RDStraw]

Jim:

Your analysis of the problem in Google Earth for Malpelo looks reasonable to
me. Do you know of someone at Google to whom such problems can be reported?

73, Dean, N6BV

> Date: Mon, 22 Aug 2011 15:57:09 -0700
> From: Jim Lux <jimlux at earthlink.net>
> Subject: Re: [TowerTalk] Terrain data for HFTA
> To: towertalk at contesting.com
> Message-ID: <4E52DEC5.8080509 at earthlink.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
>
> >
> > I  would not trust Google-Earth elevation data.To add an example like
> > Bimini,  Bahamas: Check Malpelo Island, HK0TU, 400 km away from
> the colombian
> > Pacific  coast (4.0 N, 81.6 W) According to Google earth the island is
> > submerged under  the water surface a least 340 ft. In reality,
> this island has
> > elevations over  1000 ft ASL.
> >
>
>
> I think that's a good example of which ellipsoid is being used.  if you
> move your cursor across some of the islands (little more than rocks
> sticking up, it looks like) at 3-49-57.46 N 81-36-15.28W it seems to be
> pretty consistently around -80m
>
>
> If you traverse across the island (center roughly at 4-0-12N 81-36-27W)
>
> you see the altitude smoothly vary from -80 to the SE of the island,
> getting gradually lower to -229m (at least) to the NW of the island
>
> In fact, if you look at all the elevations in the area, it runs around
> -240m everywhere, and that -60 to -80 seems to form a hump to the SW of
> the island.  It looks more like it's misregistered between the elevation
> grid and the island.  Again, that could be how the original photo image
> was georeferenced vs what the elevation data was referenced against in
> terms of datum
>
> Given the extreme depths (<-1000m) not too far away, I'm going to guess
> that Google Earth is returning bathymetry data.
>
> So, I'd say a combination of spheroid and data set mismatches.