diff --git a/geodetic.cabal b/geodetic.cabal
--- a/geodetic.cabal
+++ b/geodetic.cabal
@@ -1,5 +1,5 @@
 name:               geodetic
-version:            0.1.0
+version:            0.1.1
 license:            BSD3
 license-File:       etc/LICENCE
 author:             Tony Morris <ʇǝu˙sıɹɹoɯʇ@ןןǝʞsɐɥ>
diff --git a/src/Data/Geo/Geodetic/GreatCircle.hs b/src/Data/Geo/Geodetic/GreatCircle.hs
--- a/src/Data/Geo/Geodetic/GreatCircle.hs
+++ b/src/Data/Geo/Geodetic/GreatCircle.hs
@@ -32,12 +32,15 @@
 -- >>> fmap (printf "%0.4f") (do fr <- (-16.7889) ..#.. 41.935; to <- 6.933 ..#.. (-162.55); return (sphericalLaw (6350000 ^. nSphere) fr to)) :: Maybe String
 -- Just "17081801.7377"
 sphericalLaw ::
-  Sphere
-  -> Coordinate
-  -> Coordinate
+  (HasCoordinate c1, HasCoordinate c2) =>
+  Sphere -- ^ reference sphere
+  -> c1 -- ^ start coordinate
+  -> c2 -- ^ end coordinate
   -> Double
-sphericalLaw s start end =
-  let toRadians n = n * pi / 180
+sphericalLaw s start' end' =
+  let start = start' ^. coordinate
+      end = end' ^. coordinate
+      toRadians n = n * pi / 180
       lat1 = toRadians (fracLatitude # (start ^. latitude))
       lat2 = toRadians (fracLatitude # (end ^. latitude))
       lon1 = toRadians (fracLongitude # (start ^. longitude))
@@ -52,8 +55,9 @@
 -- >>> fmap (printf "%0.4f") (do fr <- (-16.7889) ..#.. 41.935; to <- 6.933 ..#.. (-162.55); return (sphericalLawD fr to)) :: Maybe String
 -- Just "17128743.0669"
 sphericalLawD ::
-  Coordinate
-  -> Coordinate
+  (HasCoordinate c1, HasCoordinate c2) =>
+  c1 -- ^ start coordinate
+  -> c2 -- ^ end coordinate
   -> Double
 sphericalLawD =
   sphericalLaw earthMean
@@ -75,4 +79,4 @@
     ) x) =>
     x
 sphericalLaw' =
-  optional1 sphericalLaw earthMean
+  optional1 (sphericalLaw :: Sphere -> Coordinate -> Coordinate -> Double) earthMean
diff --git a/src/Data/Geo/Geodetic/Haversine.hs b/src/Data/Geo/Geodetic/Haversine.hs
--- a/src/Data/Geo/Geodetic/Haversine.hs
+++ b/src/Data/Geo/Geodetic/Haversine.hs
@@ -32,12 +32,15 @@
 -- >>> fmap (printf "%0.4f") (do fr <- (-16.7889) ..#.. 41.935; to <- 6.933 ..#.. (-162.55); return (haversine (6350000 ^. nSphere) fr to)) :: Maybe String
 -- Just "17081801.7377"
 haversine ::
-  Sphere
-  -> Coordinate
-  -> Coordinate
+  (HasCoordinate c1, HasCoordinate c2) =>
+  Sphere -- ^ reference sphere
+  -> c1 -- ^ start coordinate
+  -> c2 -- ^ end coordinate
   -> Double
-haversine s start end =
-  let lat1 = fracLatitude # (start ^. latitude)
+haversine s start' end' =
+  let start = start' ^. coordinate
+      end = end' ^. coordinate
+      lat1 = fracLatitude # (start ^. latitude)
       lat2 = fracLatitude # (end ^. latitude)
       toRadians n = n * pi / 180
       dlat = (toRadians (lat1 - lat2)) / 2
@@ -56,8 +59,9 @@
 -- >>> fmap (printf "%0.4f") (do fr <- (-16.7889) ..#.. 41.935; to <- 6.933 ..#.. (-162.55); return (haversineD fr to)) :: Maybe String
 -- Just "17128743.0669"
 haversineD ::
-  Coordinate
-  -> Coordinate
+  (HasCoordinate c1, HasCoordinate c2) =>
+  c1 -- ^ start coordinate
+  -> c2 -- ^ end coordinate
   -> Double
 haversineD =
   haversine earthMean
@@ -79,4 +83,4 @@
     ) x) =>
     x
 haversine' =
-  optional1 haversine earthMean
+  optional1 (haversine :: Sphere -> Coordinate -> Coordinate -> Double) earthMean
diff --git a/src/Data/Geo/Geodetic/Vincenty.hs b/src/Data/Geo/Geodetic/Vincenty.hs
--- a/src/Data/Geo/Geodetic/Vincenty.hs
+++ b/src/Data/Geo/Geodetic/Vincenty.hs
@@ -63,14 +63,18 @@
 -- >>> fmap (\c' -> direct ans convergence c' (modBearing 165.34) 4235) ((-66.093) ..#.. 12.84)
 -- Just (VincentyDirectResult (Coordinate (Latitude (DegreesLatitude (-66)) (Minutes 7) (Seconds 47.0662)) (Longitude (DegreesLongitude 12) (Minutes 51) (Seconds 49.4139))) (Bearing 165.3183))
 direct ::
-  Ellipsoid
-  -> Convergence
-  -> Coordinate
-  -> Bearing
-  -> Double
+  (HasEllipsoid e, HasCoordinate c, HasBearing b) =>
+  e -- ^ reference ellipsoid
+  -> Convergence -- ^ convergence point to stop calculating
+  -> c -- ^ begin coordinate
+  -> b -- ^ bearing
+  -> Double -- ^ distance
   -> VincentyDirectResult
-direct e conv start bear dist =
-  let sMnr = e ^. semiMinor
+direct e' conv start' bear' dist =
+  let e = e' ^. ellipsoid
+      start = start' ^. coordinate
+      bear = bear' ^. bearing
+      sMnr = e ^. semiMinor
       flat = e ^. flattening
       alpha = radianBearing # bear
       cosAlpha = cos alpha
@@ -124,9 +128,10 @@
 -- >>> fmap (\c' -> directD c' (modBearing 165.34) 4235) ((-66.093) ..#.. 12.84)
 -- Just (VincentyDirectResult (Coordinate (Latitude (DegreesLatitude (-66)) (Minutes 7) (Seconds 47.0667)) (Longitude (DegreesLongitude 12) (Minutes 51) (Seconds 49.4142))) (Bearing 165.3183))
 directD ::
-  Coordinate
-  -> Bearing
-  -> Double
+  (HasCoordinate c, HasBearing b) =>
+  c -- ^ begin coordinate
+  -> b -- ^ bearing
+  -> Double -- ^ distance
   -> VincentyDirectResult
 directD =
   direct wgs84 convergence
@@ -150,7 +155,7 @@
     ) x) =>
     x
 direct' =
-  optional2 direct wgs84 convergence
+  optional2 (direct :: Ellipsoid -> Convergence -> Coordinate -> Bearing -> Double -> VincentyDirectResult) wgs84 convergence
 
 -- | Vincenty inverse algorithm.
 --
@@ -166,13 +171,17 @@
 -- >>> do fr <- 27.812 ..#.. 154.295; to <- 87.7769 ..#.. 19.944; return (inverse ans convergence fr to)
 -- Just (GeodeticCurve 7099229.9126 Azimuth 0.0000 Azimuth 180.0000)
 inverse ::
-  Ellipsoid
-  -> Convergence
-  -> Coordinate
-  -> Coordinate
+  (HasEllipsoid e, HasCoordinate c1, HasCoordinate c2) =>
+  e -- ^ reference ellipsoid
+  -> Convergence -- ^ convergence point to stop calculating
+  -> c1 -- ^ start coordinate
+  -> c2 -- ^ end coordinate
   -> Curve
-inverse e conv start end =
-  let b = e ^. semiMinor
+inverse e' conv start' end' =
+  let e = e' ^. ellipsoid
+      start = start' ^. coordinate
+      end = end' ^. coordinate
+      b = e ^. semiMinor
       f = e ^. flattening
       (phi1, phi2) =
         let rl k = radianLatitude # (k ^. latitude)
@@ -223,15 +232,15 @@
       ed = whileDo iter pred' begin
       ifi p t a = if p a then t a else a
       (alpha1, alpha2) =
-        let alphaNoConverge :: (Fractional b0, Num b0, Ord b0) => Bool -> Ordering -> b0 -> b0 -> (b0, b0)
-            alphaNoConverge c cp x y = vmap2 (ifi (>= 360) (subtract 360)) (if c
-                                                                              then (x, y)
-                                                                              else if cp == GT
-                                                                                then (180.0, 0.0)
-                                                                                else if cp == LT
-                                                                                  then (0.0, 180.0)
-                                                                                  else let nan = 0/0
-                                                                                        in (nan, nan))
+        let alphaNoConverge c cp x y =
+              vmap2 (ifi (>= 360) (subtract 360)) (if c
+                                                     then (x, y)
+                                                     else if cp == GT
+                                                       then (180.0, 0.0)
+                                                       else if cp == LT
+                                                         then (0.0, 180.0)
+                                                         else let nan = 0/0
+                                                               in (nan, nan))
         in alphaNoConverge (result ed == Converge) (compare phi1 phi2) 0 0
   in curve (b * a' ed * (sigma ed - deltasigma ed)) (modAzimuth alpha1) (modAzimuth alpha2)
 
@@ -243,8 +252,9 @@
 -- >>> do fr <- 27.812 ..#.. 154.295; to <- 87.7769 ..#.. 19.944; return (inverseD fr to)
 -- Just (GeodeticCurve 7099204.2589 Azimuth 0.0000 Azimuth 180.0000)
 inverseD ::
-  Coordinate
-  -> Coordinate
+  (HasCoordinate c1, HasCoordinate c2) =>
+  c1 -- ^ start coordinate
+  -> c2 -- ^ end coordinate
   -> Curve
 inverseD =
   inverse wgs84 convergence
@@ -267,7 +277,7 @@
     ) x) =>
     x
 inverse' =
-  optional2 inverse wgs84 convergence
+  optional2 (inverse :: Ellipsoid -> Convergence -> Coordinate -> Coordinate -> Curve) wgs84 convergence
 
 ---- not exported