after a year or so of work, i dare create a proper repo.

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+.TL
+libgeometry
+.AU
+Rodrigo G. López
+.sp
+rgl@antares-labs.eu
+.AI
+Antares Telecom Laboratories
+Albatera, Alicante
+.FS
+ACHTUNG! this is a
+.B "WORK IN PROGRESS"
+.FE
+.SH
+Introduction
+.PP
+.I Libgeometry is a computational geometry library that provides all
+the utilities anybody working with graphics or scientific simulations
+could need.
+.NH 1
+Data Structures
+.NH 2
+Point2
+.P1
+struct Point2 {
+	double x, y, w;
+};
+.P2
+.PP
+.I Point2
+represents a point in two-dimensional projective space, which itself
+is an extension of the two-dimensional euclidean space that allows us
+to work with vectors and compose affine transformations in a friendly
+manner.  A point
+.EQ
+gfont roman
+(x, y, w)
+.EN
+made out of homogenous coordinates
+.I x ,
+.I y ,
+and
+.I w ,
+yields a point with cartesian coordinates
+.EQ
+(x/w, y/w) .
+.EN
+.NH 2
+Point3
+.P1
+struct Point3 {
+	double x, y, z, w;
+};
+.P2
+.PP
+.I Point3
+is a point in three-dimensional projective space.
+.NH 2
+Matrix
+.P1
+typedef double Matrix[3][3];
+.P2
+.PP
+.I Matrix
+represents a 3x3 matrix, thought to compose affine transformations to
+apply to homogeneous 2D points.
+.NH 2
+Matrix3
+.P1
+typedef double Matrix3[4][4];
+.P2
+.PP
+.I Matrix3
+represents a 4x4 matrix, thought to compose affine transformations to
+apply to homogeneous 3D points.
+.NH 2
+Quaternion
+.P1
+struct Quaternion {
+	double r, i, j, k;
+};
+.P2
+.PP
+.I Quaternions
+are a numbering system that extends the complex numbers up to
+four-dimensional space, and are used to apply rotations and model
+mechanical interactions in 3D space.  Their main advantages with
+respect to their matrix relatives are increased computational and
+storage performance and gimbal lock avoidance.
+.NH 2
+RFrame
+.P1
+struct RFrame {
+	Point2 p;
+	Point2 bx, by;
+};
+.P2
+.PP
+A reference frame (or frame of reference) is
+.NH 2
+RFrame3
+.P1
+struct RFrame3 {
+	Point3 p;
+	Point3 bx, by, bz;
+};
+.P2
+.PP
+A reference frame (or frame of reference) is
+.NH 1
+Algorithms
+.NH 2
+Point2
+.SH
+Addition
+.P1
+Point2 addpt2(Point2 a, Point2 b)
+.P2
+.EQ
+a + b ~=~ left ( x sub a + x sub b ,~ y sub a + y sub b ,~ w sub a + w sub b right )
+.EN
+.SH
+Substraction
+.P1
+Point2 subpt2(Point2 a, Point2 b)
+.P2
+.EQ
+a - b ~=~ left ( x sub a - x sub b ,~ y sub a - y sub b ,~ w sub a - w sub b right )
+.EN
+.SH
+Multiplication
+.P1
+Point2 mulpt2(Point2 p, double s)
+.P2
+.EQ
+p * s ~=~ left ( xs,~ ys,~ ws right )
+.EN
+.SH
+Division
+.P1
+Point2 divpt2(Point2 p, double s)
+.P2
+.EQ
+p / s ~=~ left ( x over s ,~ y over s ,~ w over s right )
+.EN
+.SH
+Vector Dot Product
+.P1
+double dotvec2(Point2 a, Point2 b)
+.P2
+.EQ
+a vec ~•~ b vec ~=~ x sub a x sub b + y sub a y sub b
+.EN
+.SH
+Vector Magnitude/Length
+.P1
+double vec2len(Point2 v)
+.P2
+.EQ
+| v vec | ~=~ sqrt { x sup 2 + y sup 2 }
+.EN
+.SH
+Vector Normalization
+.P1
+Point2 normvec2(Point2 v)
+.P2
+.EQ
+n vec ~=~ left ( x over {| v vec |},~ y over {| v vec |} right )
+.EN
+.NH 2
+Point3
+.SH
+Addition
+.P1
+Point3 addpt3(Point3 a, Point3 b)
+.P2
+.EQ
+a + b ~=~ left ( x sub a + x sub b ,~ y sub a + y sub b ,~ z sub a + z sub b ,~ w sub a + w sub b right )
+.EN
+.SH
+Substraction
+.P1
+Point3 subpt3(Point3 a, Point3 b)
+.P2
+.EQ
+a - b ~=~ left ( x sub a - x sub b ,~ y sub a - y sub b ,~ z sub a - z sub b ,~ w sub a - w sub b right )
+.EN
+.SH
+Multiplication
+.P1
+Point3 mulpt3(Point3 p, double s)
+.P2
+.EQ
+p * s ~=~ left ( xs,~ ys,~ zs,~ ws right )
+.EN
+.SH
+Division
+.P1
+Point3 divpt3(Point3 p, double s)
+.P2
+.EQ
+p / s ~=~ left ( x over s ,~ y over s ,~ z over s ,~ w over s right )
+.EN
+.SH
+Vector Dot Product
+.P1
+double dotvec3(Point3 a, Point3 b)
+.P2
+.EQ
+a vec ~•~ b vec ~=~ x sub a x sub b + y sub a y sub b + z sub a z sub b
+.EN
+.SH
+Vector Cross Product
+.P1
+double crossvec3(Point3 a, Point3 b)
+.P2
+.EQ
+a vec ~×~ b vec ~=~ left ( y sub a z sub b - z sub a y sub b ,~
+			 z sub a x sub b - x sub a z sub b ,~
+			 x sub a y sub b - y sub a x sub b right )
+.EN
+.SH
+Vector Magnitude/Length
+.P1
+double vec3len(Point3 v)
+.P2
+.EQ
+| v vec | ~=~ sqrt { x sup 2 + y sup 2 + z sup 2 }
+.EN
+.SH
+Vector Normalization
+.P1
+Point3 normvec3(Point3 v)
+.P2
+.EQ
+n vec ~=~ left ( x over {| v vec |},~ y over {| v vec |},~ z over {| v vec |} right )
+.EN
+.NH 2
+Matrix
+.SH
+Addition
+.P1
+void addm(Matrix A, Matrix B)
+.P2
+.EQ
+( bold A + bold B ) sub {i,j} ~=~ bold A sub {i,j} + bold B sub {i,j}
+.EN
+.SH
+Substraction
+.P1
+void subm(Matrix A, Matrix B)
+.P2
+.EQ
+( bold A - bold B ) sub {i,j} ~=~ bold A sub {i,j} - bold B sub {i,j}
+.EN
+.SH
+Multiplication
+.P1
+void mulm(Matrix A, Matrix B)
+.P2
+.EQ
+left [ bold A bold B right ] sub {i,j} ~=~ sum from {k = 0} to 3-1 bold A sub {i,k} bold B sub {k,j}
+.EN
+.SH
+Transpose
+.P1
+void transposem(Matrix M)
+.P2
+.EQ
+( bold M sup T ) sub {i,j} ~=~ bold A sub {j,i}
+.EN
+.SH
+Identity
+.P1
+void identity(Matrix M)
+.P2
+.EQ
+bold M ~=~ left [ rpile {
+	1 ~ 0 ~ 0
+above	0 ~ 1 ~ 0
+above	0 ~ 0 ~ 1
+} right ]
+.EN
+.SH
+Determinant
+.P1
+double detm(Matrix M)
+.P2
+.EQ
+det( bold M ) ~=~ lpile {
+			m sub 00 ( m sub 11 m sub 22 - m sub 12 m sub 21 ) +
+above			m sub 01 ( m sub 12 m sub 20 - m sub 10 m sub 22 ) +
+above			m sub 02 ( m sub 10 m sub 21 - m sub 11 m sub 20 )
+}
+.EN
+.NH 2
+Matrix3
+.SH
+Addition
+.P1
+void addm3(Matrix3 A, Matrix3 B)
+.P2
+.EQ
+( bold A + bold B ) sub {i,j} ~=~ bold A sub {i,j} + bold B sub {i,j}
+.EN
+.SH
+Substraction
+.P1
+void subm3(Matrix3 A, Matrix3 B)
+.P2
+.EQ
+( bold A - bold B ) sub {i,j} ~=~ bold A sub {i,j} - bold B sub {i,j}
+.EN
+.SH
+Multiplication
+.P1
+void mulm3(Matrix3 A, Matrix3 B)
+.P2
+.EQ
+left [ bold A bold B right ] sub {i,j} ~=~ sum from {k = 0} to 4-1 bold A sub {i,k} bold B sub {k,j}
+.EN
+.SH
+Transpose
+.P1
+void transposem3(Matrix3 M)
+.P2
+.EQ
+( bold M sup T ) sub {i,j} ~=~ bold A sub {j,i}
+.EN
+.SH
+Identity
+.P1
+void identity3(Matrix3 M)
+.P2
+.EQ
+bold M ~=~ left [ rpile {
+	1 ~ 0 ~ 0 ~ 0
+above	0 ~ 1 ~ 0 ~ 0
+above	0 ~ 0 ~ 1 ~ 0
+above	0 ~ 0 ~ 0 ~ 1
+} right ]
+.EN
+.SH
+Determinant
+.P1
+double detm3(Matrix3 M)
+.P2
+.EQ
+det( bold M ) ~=~ rpile {
+		  m sub 00 ( m sub 11 ( m sub 22 m sub 33 - m sub 23 m sub 32 ) +
+			     m sub 12 ( m sub 23 m sub 31 - m sub 21 m sub 33 ) +
+			     m sub 13 ( m sub 21 m sub 32 - m sub 22 m sub 31 ) )
+above		 -m sub 01 ( m sub 10 ( m sub 22 m sub 33 - m sub 23 m sub 32 ) +
+			     m sub 12 ( m sub 23 m sub 30 - m sub 20 m sub 33 ) +
+			     m sub 13 ( m sub 20 m sub 32 - m sub 22 m sub 30 ) )
+above		 +m sub 02 ( m sub 10 ( m sub 21 m sub 33 - m sub 23 m sub 31 ) +
+			     m sub 11 ( m sub 23 m sub 30 - m sub 20 m sub 33 ) +
+			     m sub 13 ( m sub 20 m sub 31 - m sub 21 m sub 30 ) )
+above		 -m sub 03 ( m sub 10 ( m sub 21 m sub 32 - m sub 22 m sub 31 ) +
+			     m sub 11 ( m sub 22 m sub 30 - m sub 20 m sub 32 ) +
+			     m sub 12 ( m sub 20 m sub 31 - m sub 21 m sub 30 ) )
+}
+.EN
+.NH 2
+Quaternion
+.SH
+Addition
+.P1
+Quaternion addq(Quaternion q, Quaternion r)
+.P2
+.EQ
+q + r ~=~ ( r sub q + r sub r ,~ i sub q + i sub r ,~ j sub q + j sub r ,~ k sub q + k sub r )
+.EN
+.SH
+Substraction
+.P1
+Quaternion subq(Quaternion q, Quaternion r)
+.P2
+.EQ
+q - r ~=~ ( r sub q - r sub r ,~ i sub q - i sub r ,~ j sub q - j sub r ,~ k sub q - k sub r )
+.EN
+.SH
+Multiplication
+.P1
+Quaternion mulq(Quaternion q, Quaternion r)
+.P2
+.EQ
+q ~=~ [ r sub q ,~ v vec sub q ]
+r ~=~ [ r sub r ,~ v vec sub r ]
+qr ~=~ [ r sub q r sub r - v vec sub q • v vec sub r ,~ v vec sub r r sub q + v vec sub q r sub r + v vec sub q X v vec sub r ]
+.EN
+.SH
+Scalar Multiplication
+.P1
+Quaternion smulq(Quaternion q, double s)
+.P2
+.EQ
+qs ~=~ [ r sub q s ,~ i sub q s ,~ j sub q s ,~ k sub q s ]
+.EN
+.SH
+Inverse
+.P1
+Quaternion invq(Quaternion q)
+.P2
+.EQ
+q sup -1 ~=~ left ( r over {| q | sup 2} ,~ -i over {| q | sup 2} ,~ -j over {| q | sup 2} ,~ -k over {| q | sup 2} right )
+.EN
+.SH
+Magnitude/Length
+.P1
+double qlen(Quaternion q)
+.P2
+.EQ
+| q | ~=~ sqrt { r sup 2 + i sup 2 + j sup 2 + k sup 2 }
+.EN
+.NH 2
+RFrame
+.SH
+Change of reference
+.P1
+Point2 rframexform(Point2 p, RFrame rf)
+.P2
+.NH 2
+RFrame3
+.SH
+Change of reference
+.P1
+Point3 rframexform3(Point3 p, RFrame3 rf)
+.P2