Charles Dunkl (1941-) &
Don Ramirez (1943-)
"Algorithm 736: Hyperelliptic Integrals
and the Surface Measure of Ellipsoids" ACM-Trans. Math. Software, v.20 (1994) pp. 427-435.
Surface Area of an Ellipsoid
What is the surface area of an ellipsoid? [spheroid]
There are simple formulas for the surface area
of an ellipsoid of revolution,
but when the 3 semiaxes
(a, b, c) are distinct, the formula isn't elementary:
The surface area of an ellipsoid of equation
The above was originally posted here to provide a correct version of a flawed formula
given in the
Mathematica 4 documentation
[where "EllipticE" and "EllipticF" are interchanged, as
David W. Cantrell first pointed out].
As of 2005, the typo has only been corrected in the
5 documentation ...
Knud Thomsen (Denmark, 2004-04-26; e-mail)
The following symmetrical formula seems to give the surface area of a general ellipsoid
with a relative error < 1.42%.
Could it be new? [...]
S » 2p
( apbp +
bpcp ) 1/p
where p = lg(3) = ln(3)/ln(2)
The above (correct) graphic rendition won't match the previously quoted formula if
your web browser fails to provide proper legacy support for the
The "bad boys", including some versions of Safari,
Opera and Firefox, display "p" instead pf "π" and render
other kinds of unreliable gibberish in all scientific
web pages whose authors make explicit use of the "Symbol font", following the relevant
(issued in 1997 and universally supported until 2005 or so).
To be safe, you are urged to swich to a "nice guy",
like Internet Explorer or Google Chrome
(otherwise, you have to use one of the temporary solutions
Somebody must have thought of this formula before but it seems unpublished.
If you know better, please
and I'll post updates here.
Meanwhile, I shall refer to the above as
Thomsen's formula (2004-04-26).
For a very long prolate ellipsoid of revolution,
Thomsen's expression is
times the true surface area
(a relative error of about -1.41544 %).
On 2004-05-13, Knud Thomsen
(Denmark) wrote: [edited summary]
S » 4p
[ ( apbp +
bpcp ) / 3 ] 1/p
approximates the true surface area of the ellipsoid with the least relative error
(± 1.061 % worst case)
when p » 1.6075
Best regards, Knud Thomsen
This second expression is exact for a sphere regardless of the value of p,
whereas the previous one is always exact for a degenerate ellipsoid
(c = 0).
Both coincide for the value p = lg(3) = 1.5849625...
first given by Thomsen.
Knud Thomsen (2004-05-14) and David Cantrell
(2004-05-16) independently mentioned
the obvious generalization to n-dimensional ellipsoids
(with semiaxes a1, ... an )
which may be expressed in terms of the Hölder mean (H)
of the n products of n-1 semiaxes
( H = 0 when two or more semiaxes are zero):
(a1a2 ... an )
[ (a1-p + a2-p + ... +
an-p ) / n ] 1/p
an-1 ) / n 1/p
[when one semiaxis, say an, is zero]
V = Rn
pn/2 / G(1+n/2)
[R is the hypersphere radius]
S = 2 Rn-1
pn/2 / G(n/2)
= 2 H
pn/2 / G(n/2)
Scaling considerations translate into the exact formula for the hypervolume (V)
of an ellipsoid (replace Rn by
The n-1 dimensional case gives half the hyperarea of the [two sided]
degenerate n-dimensional ellipsoid, which is thus:
S' = 2 ( n1/p H )
p[n-1]/2 / G(1+[n-1]/2)
The expressions for S (hypersphere) and S' (degenerate hyperellipsoid)
are identical functions of H (generalizing the
YNOT formula for the ellipse) if:
G(n/2+1/2) / G(n/2)
G(n/2+1/2) / G(n/2)
has different elementary expressions in terms of
depending on the parity of n :
If n = 2k, then
A = p (2k-1)!! / 2k (k-1)!
= (p/2) (n-1)!! / (n-2)!!
If n = 2k+1, then
A = 2k k! / (2k-1)!!
= (n-1)!! / (n-2)!!
The limit of this value of p is 2 for [very] large values of n...
Thomsen and Cantrell both expressed some doubts about the future popularity
of such approximate formulas for the hyperareas of hyper-ellipsoids...
(2004-05-02) Approximate Surface Area of a Scalene Ellipsoid
Ellipsoids of revolution
and flat ones may be considered trivial cases...
An ellipsoid of semiaxes a, b and c is
called scalene if these three quantities are distinct, or rather [using the
inclusive viewpoint which is almost always
preferred in a mathematical context] when no two of them are known to coincide...
Let a be the largest semiaxis and c the smallest one.
Let e =
The surface area (S) of the ellipsoid has a simple expression in 3 special cases:
for an oblate or prolate ellipsoid of revolution,
and for a degenerate ellipsoid (namely, a flat spheroid
whose surface consists of the two sides of
an ellipse) :
If a = b, then
S = 2p [ a2 +
c2 atanh(e)/e ]
If b = c, then
S = 2p [ c2 +
ac arcsin(e)/e ]
Prolate ellipsoid (cigar).
If c = 0, then
S = 2p ab
The above symmetrical formula,
proposed in 2004 by the Danish geologist Knud Thomsen, is exact
for either a sphere ( a = b = c ) or a flat spheroid.
It's to the ellipsoid area what the
is to the ellipse perimeter.
Dropping the simplicity and symmetry of Thomsen's formula, it's fairly easy
to devise expressions that are correct in all three of the above trivial cases...
For example, we may define atanh(x)/x and arcsin(x)/x by continuity when x is zero
(both quantities are thus equal to 1 when x is 0) and consider the expression:
2p [ a (b-c) +
ac arcsin(u)/u + c2 atanh(v)/v ]
u = Ö(1-b2/a2)
v = Ö(1-c2/b2)
This turns out to be a poor kind of "improvement" over
Thomsen's formula except, of course,
when the ellipsoid is a solid of revolution, or nearly so.
The worst discrepancy between the two expressions
occurs when a is much larger than the other two semiaxes and c
is lb, with
l = (p/2-1)1/(p-1)
which makes Thomsen's expression
times the other (» 7.578 % larger).
As Thomsen's value is already a -1½ % underestimate,
the above is -9% off...
This goes to show that there's a price to pay for breaking up a natural symmetry
in an approximation (as asymmetrical error terms don't automatically cancel out).
This remark also applies to another approximation (< 2.1 %) proposed in 2003
by Dr. Andreas Dieckmann (of Bonn University) in terms of
r = arcsin(e)/e :
This gives the correct area
S = 2pc (c+ar)
for prolate spheroids.
On 2004-05-17, we received the first attempt at optimizing a symmetrical
formula by Knud Thomsen, who investigated the following expression, featuring
a second parameter (k) generalizing his earlier formula (the case k = 0):
The formula is designed to be correct in the case of a sphere for all values of p and k.
Selecting p = ln(2) / ln(p/2), Thomsen claims optimal results
when k is around 0.0942 and suggests the
convergent 3/32 (0.9375)
which is good enough to yield a relative error between
-0.204 % and +0.187 %
[the next convergents would be 5/53 and 8/85].
This represents an improvement of one order of magnitude over his
original formula (k=0).
Earlier work of Achim Flammenkamp
(of Universität Bielefeld, Germany)
along similar lines was brought to our attention on 2004-06-14 by his colleague
Building on an article of Klamkin, Flammenkamp
investigated several approximations to the surface area of an ellipsoid around 1990,
including the following two expressions.
The first one has only a 10% accuracy,
whereas a worst relative error of 2.09% is claimed for the second formula.
S » 2p
[ ( ab + ac + bc )
- 3 abc / (a+b+c) ]
S » p
( ab + ac + bc )
( a2b2 +
b2c2 )½ ]
From 1994 notes (2006-10-20)
The nautical mile (officially: 1852 m)
A lesson in averages... over the surface of an oblate spheroid.
Originally, one nautical mile was meant to correspond to the distance between
two points on the Ocean separated by a geocentric
angle of one minute (1°/60).
Taking into account the oblateness of the Earth, the nautical mile should be defined,
more precisely, as an "average" minute of latitude.
Following a 1929 resolution of the International Hydrographic Conference,
the international nautical mile (NM)
is now officially defined as exactly equal to 1852 m.
(This conventional definition had been legal in France since 1906.)
The so-called "British Admiralty" nautical mile also has a conventional value:
6080 ft, or exactly 1853.184 m.
If the meter was still defined in reference to the Meridian, there would be
exactly 10 000 000 meters in a quarter meridian, corresponding to a change
in latitude of 5400 minutes.
A "typical" single minute of latitude would
then be equal to 100000/54 or about 1851.852 m.
To the nearest whole number of meters,
this gives the above definition of the international nautical mile.
The nautical mile formerly used in the United States had a different definition:
1/21600 of the meridian of the so-called Clark spheroid
(which is a sphere having the same surface as the Earth).
Modern values for the Reference Ellipsoid (see below)
would put the radius of Clark's spheroid at about 6371007.181 m and
the "conventional" value of the
US nautical mile at 1853.250866 m (6080.219 ft, or 6080.207 "US Survey" ft).
The true shape of the Earth (the so-called "geoid") is
defined as an equipotential surface
(i.e., a surface which is everywhere perpendicular to
the local vertical indicated by a plumb line).
Such a shape turns out to be quite complicated,
but its irregularities are best charted in comparison
with a close "regular" approximation, the
Reference Ellipsoid, whose exact
shape and size have been defined in 1979, in Canberra (IUGG 1980).
The Reference Ellipsoid is defined to have the following characteristics:
Equatorial radius (a) exactly equal to 6378137 m.
Oblateness f = 1 / 298.257222101 =
1 - b/a
The polar radius b = a (1- f )
is the distance of either pole to the center.
The Meridian is an ellipse of eccentricity
e = Ö(2f-f 2 ) = 0.0818191910428.
The length of the reference Meridian is thus:
The "uncertainty" stated (between parentheses) is in units of the last significant digit shown
and corresponds to an "uncertainty" of half a unit in the least significant digit of the
value for the oblateness f specified above.
That's a ludicrous precision of 120 nm.
Divide this by 21600 and you obtain:
Forsaking most of the ludicrous precision, we may state this result in terms
of the aforementioned international nautical mile (NM) henceforth equal to 1852 m.
1852.216 m = 1.000117 NM
Now, none of the above computations
yield the proper "average minute of latitude" on that spheroid.
Actually, proper averaging yields subtler and simpler results
with expressions involving only elementary functions and shunning
all the arcana related to the
perimeter of an ellipse.
Like many questions about averages,
this one can only be properly addressed if probabilistic assumptions are made explicit:
Let's do our "averaging" by giving equal weight to any
square inch on the surface of the Globe.
This is the simplest natural approach which refers only
to the spheroid's geometry, shunning ad hoc alternatives for the
real Earth (like considering only open oceans, or even weighing maritime
routes according to their estimated traffic).
Thus, a "random" point on the Earth is more likely to be at a low latitude
than a high one. Loosely speaking, there are "more points" in the vicinity
of the equator, at latitude 0°, than in the North Pole's vicinity, at
On a sphere, for any infinitesimal positive quantity
a random latitude would be between q and
q+d with probability
½ cos(q) d.
The correct "weighing" for an oblate spheroid is somewhat more complicated and
yields the following (exact) formula, in terms of the radius of the equator
(a) and the eccentricity of the meridian (e):
Average Minute of Geocentric Latitude For the Earth, this is : 1853.256 m = 1.000678 NM
2 [ 1 - e2 ( 1 - 2 e2 / 15) ]
(1 + (1-e2 ) atanh(e) / e )
The second factor in the right-hand side is close to unity for small values
of e, but it can become large when e approches one.
Technically, the value of an average minute of latitude is indeed infinite
for a flat disk (e = 1).
The difference with the "British Admiralty nautical mile" of 6080 ft
is less than 3 inches, and the former definition (6080.2 ft) of the US
nautical mile is only a centimeter off the mark.
These two are indeed good
approximations to the "average minute of latitude", while the more naive
"new" nautical mile of 1852 m is over a meter short!
This is not the end of the story, though.
So far, the "latitude" we spoke
about has been the "geocentric" one: the angle between the plane of the
equator and a line going through the center of the Earth.
This is not the "geodetic"
latitude which is really seen by navigators who measure the angle
between the horizon (or a vertical line, which does not go through the
center of the Earth) and a fixed direction, like the celestial pole.
If the Earth was a sphere, there would not be any difference whatsoever.
Also, since there are still 21600 "geodetic" minutes of latitude in a full
meridian; this yields the same "naive" average of 1852.216 m as for the
Things change when we average "correctly" over the
surface of the globe: First, we observe that distance changes along a
meridian with geodetic latitude at a rate (per radian) equal to the
meridian's radius of curvature —this is one way the radius of curvature
can be defined, for any planar curve.
Thus, at a point where the
radius of curvature of the meridian is R, the geodetic minute of latitude
is equal to Rp/10800.
The average (over the ellipsoid's surface) of R is
6356828.89 m, which gives a low value (1849.12657 m) for the average
"geodetic" mile, almost 3 meters short of the international nautical mile.
The corresponding formula is very similar to the "geocentric" one:
Average Minute of Geodetic Latitude For the Earth, this is : 1849.127 m = 0.998448 NM
2 [ 1 - e2 ( 4/3 - 8 e2 / 15) ]
(1 + (1-e2 ) atanh(e) / e )
This is smaller than the geocentric expression for roundish spheroids
but becomes higher when the polar radius is below
or about 40.825% of the equatorial radius.
Compared to the geodetic latitude, the geocentric value
is between 33.333% lower (for e near 1)
and 14.564% higher
(for e = Ö(9-Ö21)/Ö8) ).
A great ellipse on an ellipsoid is defined as the intersection
of the surface of the ellipsoid with a plane that goes through its center.
Great ellipses are not necessarily geodesics (which is
to say that the shortest path betwen two points on the surface of an ellipsoid
isn't always an arc of a great ellipse).
If the center of the ellipsoid and two points on its surface are aligned, those
two points are said to be antipodal.
The great ellipses through two antipodal points may have different lengths.
Sidey P. Timmins,
U.S. Census Bureau (2012-01-09)
Curved Surface Area with a Given Boundary on the Surface of the Earth
What area is delimited by a closed curve on an oblate spheroid?
On an oblate ellipsoid of revolution with equatorial radius a
and polar radius b, let's consider the curved surface area
bounded by a "rectangle" consisting of the equator,
two arcs of meridians and an arc of the parallel line of constant
We tally that surface area positively
in the Northern Hemisphere and negatively
in the Southern Hemisphere when going from West to East (increasing longitudes)
and vice-versa westward.
That area is directly proportional to the difference between
the longitudes of the two meridians. The coefficient of proportionality is
some odd function f (which shall be computed
below) of the aforementioned geodetic latitude.
In particular, for an infinitesimal longitude difference
dq, the above curved rectangle encloses the following
infinitesimal surface area:
- f (j)
The negative sign makes the above consistent with the
sign convention used
for planar areas.
The equator oriented eastward plays the rôle of the x-axis
and the northward meridian is analoguous to the y-axis.
Indeed, in the Northern hemisphere where f
is positive, a positive dq
corresponds to a clockwise boundary
(eastward at the given longitude and
westward back on the equator)
which must encircle a negative infinitesimal area, by convention.
Along a closed loop
(possibly specified by giving
as a periodic function of a parameter t )
the contour integration of the above
would give the area enclosed by the curve
only if doesn't go around the polar axis.
To remove this inconvenient restriction
(which has no counterpart in planar geometry) we shall consider instead
the infinitesimal area swept by the arc of a meridian originating at the
North pole, counted positively eastward :
[ f (p/2)
- f (j) ]
The integral of that is the correct area encircled by the curve
(defined only modulo
the total surface area of the ellipsoid)
even if the curve goes around the polar axis many times.
(The area bounded by a self-crossing loop is tallied like
in the planar case, as depicted at right.)
Signed Area Encircled by a Closed Curve
Drawn on a Spheroid :
A = ò
[ f (p/2)
- f (j) ]
[ f (p/2)
- f ( j(t) ) ]
q' (t) dt
The general expression of f can be obtained by means of
cartesian coordinates (well, cylindrical ones, actually).
The correspondance with geodetic coordinates is
given elsewhere on this site).
The basic infinitesimal rectangular surface area is equal to the displacement
r dq along the parallel multiplied into the
(perpendicular) displacement ds along the meridian:
df dq =
r dq ds =
r dq dz
[ 1 + (dr/dz)2 ]½
Using the equation of the meridian
(r/a)2 + (z/b)2 = 1 we obtain:
df = r dz
[ 1 + (dr/dz)2 ]½
dr/dz = -(a/b)2 z/r
It works! A very simple formula - wow! [...] Thank you.
Total Surface Area of an Oblate Spheroid :
The surface area of the Northern hemisphere being
2 p f (p/2)
the surface area of the entire oblate spheroid is thus shown to be
4 p f (p/2)
which boils down to the very nice formula
Surface Area of an Oblate Spheroid
a 2 + b 2 atanh(e)/e
For a sphere
( a = b and e = 0 ) that's
4 p a 2
Area Bounded by a Closed Polygonal Line :
Sidey Timmins' original question was actually about the case where the boundary
curve is a "polygonal" line.
The value of the above integral can be obtained through the following
trapezoidal approximation (which does turn into an
exact formula when the special type of "straight" lines
investigated below is used to join one vertex of the polygon
to the next).
Area Bounded by a Noncircumnavigating Polygonal Line
= òf (j)
= Sif ( ji )
( qi+1 -
qi-1 ) / 2
In this, there are n vertices in the polygon
and the indices involved are understood to be
(the points of indices 0 and n coincide).
(2012-01-22) "Pseudo-Straight Lines" on an Oblate Spheroid
Curves that sweep out areas varying quadratically with longitude.
When used as the sides of polygonal boundaries,
such curves turn the above
trapezoidal approximation into an exact formula.
With the notations of the previous section,
those curves feature an increase in f
proportional to the increase in longitude:
d f = k dq
f (j) =
fo + k q
A parametrical family of curves is thus explicitely defined
which does not appear to have any particularly enlightening characteristics...
By the Gauss-Bonnet theorem, those curves would actually be
geodesics on a surface of revolution of constant Gaussian curvature
(sphere or pseudo-sphere). This is not the case for an oblate ellipsoid,
but it's close enough for practical purposes when the vertices are not widely
separated (so the variations in curvature from one vertex to the next are negligible).