update readme

README.md

@@ -1,13 +1,10 @@
 # mappers
 
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 Pure Rust geographical projections library. Similar to `Proj` in basic functionality but allows for a use in concurrent contexts.
 
@@ -64,20 +61,29 @@ println!("lon: {}, lat: {}", lon, lat); // lon: 6.8651, lat: 45.83260000001716
 
 Some projections are mathematically exactly invertible, and technically geographical coordinates projected and inverse projected should be identical. However, in practice limitations of floating-point arithmetics will introduce some errors along the way, as shown in the example above.
 
-## Multithreading
+## ConversionPipe
+
+This crate also provides a struct `ConversionPipe` that allows for easy
+conversion between two projections. It can be constructed directly from
+`Projection` with `pipe_to` method or directlywith `ConversionPipe::new()`.
 
-For projecting multiple coordinates at once, the crate provides `_parallel`
-functions that are available in a (default) `multithreading` feature. These functions
-use `rayon` crate to parallelize the projection process. They are provided
-mainly for convenience, as they are not much different than calling
-`.par_iter()` on a slice of coordinates and mapping the projection function over it.
+### Example
 
 ```rust
-let lcc = LambertConformalConic::new(2.0, 0.0, 30.0, 60.0, Ellipsoid::WGS84)?;
+// We start by defining the source and target projections
+// In this case we will use LCC and LongitudeLatitude
+// to show how a normal projection can be done with ConversionPipe
+let target_proj = LambertConformalConic::new(2.0, 0.0, 30.0, 60.0, Ellipsoid::WGS84)?;
+let source_proj = LongitudeLatitude;
+
+let (lon, lat) = (6.8651, 45.8326);
 
-// Parallel functions use slices of tuples as input and output
-let geographic_coordinates = vec![(6.8651, 45.8326); 10];
+// Now we can convert to LCC and back to LongitudeLatitude
+let (x, y) = source_proj.pipe_to(&target_proj).convert(lon, lat)?;
+let (pipe_lon, pipe_lat) = target_proj.pipe_to(&source_proj).convert(x, y)?;
 
-let map_coordinates = lcc.project_parallel(&geographic_coordinates)?;
-let inversed_coordinates = lcc.inverse_project_parallel(&map_coordinates)?;
+// For simple cases the error remains small
+// but it can quickly grow with more complex conversions
+assert_approx_eq!(f64, lon, pipe_lon, epsilon = 1e-10);
+assert_approx_eq!(f64, lat, pipe_lat, epsilon = 1e-10);
 ```