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[aprssig] PHG and HAAT, more.

Dave Baxter dave at emv.co.uk
Fri Oct 14 11:55:24 UTC 2005


>> HAAT by the FCC definition (and I am quoting from memory and might
have parts of this wrong) are that you draw 36 radials out at 10 degree
intervals from your location.  You then take 50 evenly spaced elevation
data readings between 3 and 16 km along each of the lines.  These get
averaged and a number is derived.  I have many locations along these
radials from my house that are four to five hundred feet above my
elevation when I trace out the lines to 16 km away.  This is how you get
a negative number.  The Height is above the average terrain around you
in a 16 km radius.  This is why it gets difficult to just guess at the
number by looking around you in a hilly area.  In your transmitter is
located in a deep valley you will most likely have a negative number for
your HAAT.
-*End Snip*-

Thanks for that..  (Wow.. km's too!)

Seems to me, that it's totally useless in parts of the world, such as
Wales, Scotland, Switzerland and other "non flattish" places such as
parts of California and other similar areas, even within the USA...

It also needs people to be able to read and understand a map (even have
one in their possession that shows height data) something that is
becoming very rare in these days of web based mapping, sadly.  Anyone
know of a web based mapping system that shows the terrain height at the
cursor, outside of the USA?..

If you have Memory Map, or a similar system loaded, you can draw the 36
radials, and read the height out along the "paths" the system thinks
they are.

More flames I suspect...  (Oooo. I just love stirring these things up!
But it get's people thinking again.)

Dave G0WBX.

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