Location, location

Reynolds, Alfred Alfred.Reynolds at dsto.defence.gov.au
Wed Oct 17 14:48:57 EST 2001

Unfortunately DTED2 (30m posts) is not available (the shuttle has mapped it
tho) for Australia (might be available soon, its going to be huge at 54mb
per 1 degree square tho). What is really needed is some kind of dynamic
vector representation eh? ;) 

> -----Original Message-----
> From: Tony Langdon [mailto:tlangdon at atctraining.com.au]
> Sent: Wednesday, October 17, 2001 2:43 PM
> To: 'Reynolds, Alfred'; 'David Leonard'; 'alfred at mazuma.net.au'
> Cc: wireless at lists.samba.org
> Subject: RE: Location, location
> > DTED1 is a 3 sec arc which equates to about 90m on the ground. It is
> > topographic only (it used to be/still is derived from people reading
> > topographic maps and inputting the data). Buildings would 
> > certainly be a
> Hmm, where I live, this isn't accurate enough.  I ran off 
> some path analyses
> using software which has topographic data accurate to 100m.  
> It got some
> paths totally wrong, saying it was LOS, when it wasn't (one 
> only has to
> stand outside and peer at the lump of dirt in the middle of 
> the so called
> "LOS path" ;) ).  I am talking about purely natural 
> topographic features
> here, not buildings or cuttings.
> My problem is I'm on the side of a steep valley, which is a 
> couple hundred
> metres across at most, and the software didn't see the full 
> depth of the
> valley, making gradients in the east/west direction look a 
> lot less than
> they really are.  I think 20m data points are necessary 
> around my area to
> get a half decent picture of what's going on...
> Let's say that around 60-70m to the east, you're on the 
> plateau that is much
> of the northern suburbs (Essendon a/p is a part of this one). 
>  Less than
> 100m to the west, and you're in a BIG hole - only way out is aircraft
> reflections (I've done that on VHF!) from planes around 
> Tulla.  Go just a
> little further west again, maybe 100m or less and you're back 
> at my level,
> or higher.
> But these maps will still be good for most people.  Just 
> posting my bit of
> experience, to say sometimes, one needs better data than what 
> is claimed to
> be "good enough".

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