Re: [Boost-users] Boost-users Digest, Vol 3016, Issue 2

Subject: Re: [Boost-users] Boost-users Digest, Vol 3016, Issue 2
From: Andrew Maclean (andrew.amaclean_at_[hidden])
Date: 2012-03-04 17:42:30

>
> ---------- Forwarded message ----------
> From: Barend Gehrels <barend_at_[hidden]>
> To: boost-users_at_[hidden]
> Cc:
> Date: Sun, 04 Mar 2012 18:01:52 +0100
> Subject: Re: [Boost-users] [Geometry] Calculating distances on the earth
>  Hi Sean,
>
> On 4-3-2012 17:14, Sean Farrow wrote:
>
>  Hi all:****
>
> I need to calculate distances on the earth. Ideally I’d like to use the
> haversine formula.****
>
> There is an example in the docs at:****
>
>
> http://www.boost.org/doc/libs/1_49_0/libs/geometry/doc/html/geometry/quickstart.html
> ****
>
> under the non-Cartesian heading.****
>
> Will this do what I need, or do I need the Geographical coordinate system,
> (if yes where is this available and what features does this supply?)****
>
>
> This will do what you ask for. So it will calculate distances on the Earth
> using the Haversine formula.
>
> However, it considers the Earth as a perfect sphere, which it is not. So
> distances are rough approximations.
>
> If you need more precise results indeed you will need the Geographic
> coordinate system, and the distances then use Andoyer which is much more
> precise.
>
> That is not included in the current Release. So if you need it you have to
> download the Trunk of Boost, and it is there available as an extension.
>
> See the examples here:
>
> https://svn.boost.org/svn/boost/trunk/libs/geometry/example_extensions/gis/latlong/
>
> Regards, Barend
>
>
>
>
> ---------- Forwarded message ----------
> From: Sean Farrow <sean.farrow_at_[hidden]>
> To: "boost-users_at_[hidden]" <boost-users_at_[hidden]>
> Cc:
> Date: Sun, 4 Mar 2012 17:13:21 +0000
> Subject: Re: [Boost-users] [Geometry] Calculating distances on the earth
>
> Hi: ****
>
> Ok, thanks, What (roughly) is the difference in precision? I’m using this
> to determine the distance between two buildings.****
>
> Cheers****
>
> Sean.****
>
> ** **
>
> *From:* boost-users-bounces_at_[hidden] [mailto:
> boost-users-bounces_at_[hidden]] *On Behalf Of *Barend Gehrels
> *Sent:* 04 March 2012 17:02
> *To:* boost-users_at_[hidden]
> *Subject:* Re: [Boost-users] [Geometry] Calculating distances on the earth
> ****
>
> ** **
>
> Hi Sean,
>
> On 4-3-2012 17:14, Sean Farrow wrote: ****
>
> Hi all:****
>
> I need to calculate distances on the earth. Ideally I’d like to use the
> haversine formula.****
>
> There is an example in the docs at:****
>
>
> http://www.boost.org/doc/libs/1_49_0/libs/geometry/doc/html/geometry/quickstart.html
> ****
>
> under the non-Cartesian heading.****
>
> Will this do what I need, or do I need the Geographical coordinate system,
> (if yes where is this available and what features does this supply?)****
>
>
> This will do what you ask for. So it will calculate distances on the Earth
> using the Haversine formula.
>
> However, it considers the Earth as a perfect sphere, which it is not. So
> distances are rough approximations.
>
> If you need more precise results indeed you will need the Geographic
> coordinate system, and the distances then use Andoyer which is much more
> precise.
>
> That is not included in the current Release. So if you need it you have to
> download the Trunk of Boost, and it is there available as an extension.
>
> See the examples here:
>
> https://svn.boost.org/svn/boost/trunk/libs/geometry/example_extensions/gis/latlong/
>
> Regards, Barend
>
> ****
>
>
> ---------- Forwarded message ----------
> From: Barend Gehrels <barend_at_[hidden]>
> To: boost-users_at_[hidden]
> Cc:
> Date: Sun, 04 Mar 2012 18:36:11 +0100
> Subject: Re: [Boost-users] [Geometry] Calculating distances on the earth
>  Hi Sean,
>
> On 4-3-2012 18:13, Sean Farrow wrote:
>
>  Hi: ****
>
> Ok, thanks, What (roughly) is the difference in precision? I’m using this
> to determine the distance between two buildings.****
>
>
> The sampes give an idea, but that is between cities (miles away). Between
> buildings the difference will be  less, but I've not tested it. So the best
> is to test that yourself (and the results are interesting for the list ;-) )
>
> Regards, Barend
>
>
>
> ---------- Forwarded message ----------
> From: Sean Farrow <sean.farrow_at_[hidden]>
> To: "boost-users_at_[hidden]" <boost-users_at_[hidden]>
> Cc:
> Date: Sun, 4 Mar 2012 17:49:04 +0000
> Subject: Re: [Boost-users] [Geometry] Calculating distances on the earth
>
> Hi: ****
>
> I’ll test this and get back to the list. Do we have any idea as to
> whether/when the extension(s) will become part of the official distribution?
> ****
>
> Cheers****
>
> Sean.****
>
> *From:* boost-users-bounces_at_[hidden] [mailto:
> boost-users-bounces_at_[hidden]] *On Behalf Of *Barend Gehrels
> *Sent:* 04 March 2012 17:36
> *To:* boost-users_at_[hidden]
> *Subject:* Re: [Boost-users] [Geometry] Calculating distances on the earth
> ****
>
> ** **
>
> Hi Sean,
>
> On 4-3-2012 18:13, Sean Farrow wrote: ****
>
> Hi: ****
>
> Ok, thanks, What (roughly) is the difference in precision? I’m using this
> to determine the distance between two buildings.****
>
>
> The sampes give an idea, but that is between cities (miles away). Between
> buildings the difference will be  less, but I've not tested it. So the best
> is to test that yourself (and the results are interesting for the list ;-) )
>
> Regards, Barend****
>
>

If you are using latitude/longitude then these methods will work:
1)  Consider implementing Vincentys method, proposed by Thaddeus Vincenty,
 and is documented at
http://www.ngs.noaa.gov/PUBS_LIB/inverse.pdf,  I believe this has a
precision of around 0.5mm. Be careful to avoid domain errors near the
poles. This has the advantage of also calculating forward and back azimuth.

2) Andoyer's method which also takes flattening into account but loses
precision for very short distances.

Alternatively since you are working with short distances implement
Redfearn's formulae to generate UTM coordinates and then use planar
geometry.

For more information see:
http://www.ga.gov.au/geodesy/datums/calcs.jsp#trans
There is a pdf manual (containing all the formulae) (
http://www.icsm.gov.au/gda/gdatm/index.html)  and excel worksheets along
with on-line calculators that you can use here.

Regards
   Andrew

-- 
___________________________________________
Andrew J. P. Maclean
___________________________________________