On 8/20/11 4:53 AM, TexasRF@aol.com wrote:
> Sounds like someone's earth bulge corrections are amiss! This is the name
> used due to the earth shape being slightly ellipsoid instead of a perfect
> sphere. The earth diameter is slightly greater at the equator than higher
> or lower latitudes.
Slightly? some 25 km, more like it. (1 part in 286, roughly) (the
peak of Everest is not the farthest point from the Earth's center...
Chimborazo in Ecuador is, because it's right on the Equator.
Kilimanjaro probably gives it a run for the money, it's close to the
Equator too, and tall)
I'd find it hard to believe that google earth would not use some
reference ellipsoid (clarke 1866 or wgs84 would be likely choices), but
they could have chosen the wrong one for the data.
However, I don't that is all that likely, since they're merging map data
and imagery from all over the world, they already have to deal with
transforming a data set from one ellipsoid to another.
>
>
> If this is the case, then it seems that the elevation of all locations
> near the HK area would be in error.
>
> We have to account for earth bulge in our EME az/el calculations so it is
> a real effect; not just imagined.
>
>
> 73,
> Gerald K5GW
>
>
>
> In a message dated 8/19/2011 10:48:12 P.M. Central Standard Time,
> hk1kxa@hotmail.com writes:
>
>
> 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.
>
> David
> HK1A
> EC5KXA
> AE5XQ
>
>
>> From: n6bv@arrl.net
>> To: towertalk@contesting.com
>> Date: Wed, 17 Aug 2011 11:29:16 -0700
>> Subject: [TowerTalk] Terrain data for HFTA
>>
>> Charlie:
>>
>> You said recently:
>>
>>> Date: Tue, 16 Aug 2011 20:12:45 -0500
>>> From: Charlie Carroll<k1xx@cfl.rr.com>
>>> Subject: Re: [TowerTalk] grabbing terrain data for HFTA
>>> To: Grant Saviers<grants2@pacbell.net>, towertalk@contesting.com
>>> Message-ID:<wg1l6uo0lqvcmp2rougptbc7.1313543269277@email.android.com>
>>> Content-Type: text/plain; charset=utf-8
>>>
>>> Door's abt to close, so have to be brief. Of late, I have taken
>>> to semi-automatically extracting terrain data from Google Earth.
>>> I dump this info into an Excel spreadsheet for the number
>>> crunching. Pretty painless to do something like ten foot
>>> intervals out to 10k feet.
>>>
>>> 73 charlie, k1xx
>>
>> N6BV: I'm not sure where Google Earth gets their terrain data, but I am
>> suspicious that it is derived at least partially from the SRTM (Shuttle
>> Radar Topography Mission) data set. I get nervous when I look at the
> terrain
>> data for islands surrounded by seawater -- which should, by definition,
> be
>> at or at least very close to sea level. It is often shown as being
>> considerably different from sealevel.
>>
>> N6BV: For example, in Google Earth zoom into Baileytown, Bimini, Bahamas.
>> Just to the west of Baileytown the altitude goes considerably negative.
>> Either this is a depthsounder reading (which I doubt) or else something
> is
>> goofy!
>>
>> N6BV: I'm curious how you are extracting that data from Google Earth
>> semi-automatically, even if I'm nervous about the data itself.
>>
>>>
>>> Grant Saviers<grants2@pacbell.net> wrote:
>>>
>>>> Can some one share a pointer for up to date instructions for grabbing
>>> >the terrain data from the web for HFTA? Every instruction I've found
> is
>>>> hopelessly out of sync with the current terrain data web site.
>>>>
>>>
>
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