Location, location

Reynolds, Alfred Alfred.Reynolds at dsto.defence.gov.au
Wed Oct 17 13:56:32 EST 2001

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
problem but I suspect that its only really an issue for those in heavily
built up areas (which means its not a problem for people in Canberra ;).
Fresnel zone clearance with buildings will be an issue, but as a rough guide
it will be close enough. I do not know of a source of info that contains
structures (dted1 is +/- 30m in the vertical....), if someone does I would
love to know about it :)

As for the data itself, it comes in 1 degree wide chunks (with the filename
denoting the sw corner of the data), with each file being about 2.76mb. I
will upload the data to a webserver I have access to when I get home and
then post a URL here. 

> -----Original Message-----
> From: David Leonard [mailto:david.leonard at itee.uq.edu.au]
> Sent: Wednesday, October 17, 2001 1:23 PM
> To: Reynolds, Alfred
> Cc: wireless at lists.samba.org
> Subject: RE: Location, location
> On Wed, 17 Oct 2001, Reynolds, Alfred typed thusly:
> > I can supply a reasonably complete set of digital terrain 
> data for the
> > eastern sea board in DTED level 1 format (which is fine for 
> radio line of
> > sight work). I also have the c code to load the data and 
> produce height
> > profiles :) I may even be able to provide code to spit out 
> path losses
> > between two points (I need to double check copyright on that).
> >
> > What I don't have lots of is time :)
> > The data is about 500mb worth, if someone is interested I 
> will look into
> > making up a web frontend to the data and algorithms (right 
> now I have a java
> > based app).
> David Arnold just alerted me to this thread...  Mmmm, DTED level 1...
> The AUSLIG DEM i got was 9 second res and has shown to be 
> problematic in two
> ways:
> 	- it's almost useless for people nearby each other (ie 
> within 1km)
> 	  since its so coarse
> 	- its data from a *surface model*.. ie buildings, trees, etc.
> 	  structures are removed and its just the ground level... so
> 	  it gives misleading plots in some cases.
> DTED 1 (www.fas.org/irp/program/core/dted.htm) is 3 second 
> arc (~100m res)
> and (although I'm not sure) it is also a surface model that 
> ignores structures?
> Can you confirm this?
> Alfred, it would be really nice if you could put up a HTTP 
> interface that
> allowed people to retreive raw segments of your data... of 
> course perhaps
> limited to say squares of size 1 minute of arc? :)
> I would certainly extend the brismesh mapping tools to make 
> use of that! :)
> d
> -- 
> David Leonard                           David.Leonard at itee.uq.edu.au
> Dept of Inf. Tech. and Elec. Engg   _   Ph:+61 404 844 850
> The University of Queensland       |+|  
QLD 4072  AUSTRALIA               ~` '~

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