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[TowerTalk] Terrain data for HFTA

To: <>
Subject: [TowerTalk] Terrain data for HFTA
From: "RDStraw" <>
Date: Wed, 17 Aug 2011 11:29:16 -0700
List-post: <">>

You said recently:

> Date: Tue, 16 Aug 2011 20:12:45 -0500
> From: Charlie Carroll <>
> Subject: Re: [TowerTalk] grabbing terrain data for HFTA
> To: Grant Saviers <>,
> Message-ID: <>
> 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

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 <> 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.
> >
> >Grant KZ1W

> Date: Wed, 17 Aug 2011 06:24:03 -0400
> From: Pete Smith <>
> Subject: Re: [TowerTalk] grabbing terrain data for HFTA
> To: Charlie Carroll <>
> Cc:, Grant Saviers <>
> Message-ID: <>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> Charlie, this sounds like an excellent solution - potentially much less
> involved than the old way of using MicroDem and the USGS website.  If
> you can provide a few more details, I'll be glad to write it up, and I'd
> bet that N6BV and the ARRL will be interested in making it available on
> the ARRL web-site.  Dean and I wrote most of the old instructions you'll
> find, but it always was a PITA because USGS kept changing their web-site.
> 73, Pete N4ZR


N6BV: This is the latest operating instructions for HFTA, dated Aug 3, 2009.
I checked the links for obtaining DEM, NED and SRTM data and they all work.

Grant: It may be useful for you to check out a webinar I gave. It's entitled
"Hinks and Kinks for Using HFTA" and can be found on the PVRC website:

73, Dean, N6BV


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