[postgis-users] decimal degrees -> miles?

[Timothy H. Keitt]

There are some more general solutions as well at: 

	http://www.census.gov/cgi-bin/geo/gisfaq?Q5.1

T.

On Sun, 2002-08-25 at 20:52, Doug Nebert wrote:
> Alex Rice wrote:
> > Hi, does PostGIS have a function for converting decimal degrees to 
> > miles? I'm using a -1 projection and my data is in decimal degrees.
> > 
> 
> If you wish to calculate the distance in miles approximately
> based on coordinate pairs in decimal degrees, the EPA has
> been using this set of equations for years. Perhaps a method
> could be added in postGIS to calculate the linestring distance
> if the units are dd. It compensates for the fact that the
> distance in longitude units converges towards the poles. It
> will be most correct obviously for more detailed lines:
> 
> The equations below can be used compute the distance in miles
> between two points (lat1/lon1 and lat2/lon2) that are expressed in
> decimal degrees. You would have to sum the calculated segment
> distances for the linestring.
> 
> disty = 68.98 * (lat1-lat2)
> distx = 69.27 * cosine(lat2) * (lon1-lon2)
> length = sqrt(disty*disty + distx*distx)
> 
> Doug.
> 
> 
> > Thanks,
> > 
> > Alex Rice, Software Developer
> > Architectural Research Consultants, Inc.
> > alex_rice at arc.to
> > alrice at swcp.com
> > 
> > 
> > 
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> 
> 
> 
> 
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