[TowerTalk] Terrain data for HFTA

[TexasRF at aol.com]

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.
 
 
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 at 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 at arrl.net
> To: towertalk at 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 at cfl.rr.com>
> > Subject: Re: [TowerTalk] grabbing  terrain data for HFTA
> > To: Grant Saviers  <grants2 at pacbell.net>, towertalk at contesting.com
> > Message-ID:  <wg1l6uo0lqvcmp2rougptbc7.1313543269277 at 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 at 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.
> > >
> >

_______________________________________________



_______________________________________________
TowerTalk  mailing  list
TowerTalk at contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk