Source code for alvinxy.alvinxy

'''
AlvinXY Utility Module

All of this is based on WHOI's original implementations in C and MATLAB.

'''

from math import *
import numpy as np

def  mdeglat(lat):
    '''
    Provides meters-per-degree latitude at a given latitude
    
    Args:
      lat (float): latitude

    Returns:
      float: meters-per-degree value
    '''
    latrad = lat*2.0*pi/360.0 ;

    dy = 111132.09 - 566.05 * cos(2.0*latrad) \
         + 1.20 * cos(4.0*latrad) \
         - 0.002 * cos(6.0*latrad)
    return dy

def mdeglon(lat):
    '''
    Provides meters-per-degree longitude at a given latitude

    Args:
      lat (float): latitude in decimal degrees

    Returns:
      float: meters per degree longitude
    '''
    latrad = lat*2.0*pi/360.0 
    dx = 111415.13 * cos(latrad) \
         - 94.55 * cos(3.0*latrad) \
	+ 0.12 * cos(5.0*latrad)
    return dx

def ll2xy(lat, lon, orglat, orglon):
    '''
    AlvinXY: Lat/Long to X/Y
    Converts Lat/Lon (WGS84) to Alvin XYs using a Mercator projection.

    Args:
      lat (float): Latitude of location
      lon (float): Longitude of location
      orglat (float): Latitude of origin location
      orglon (float): Longitude of origin location

    Returns:
      tuple: (x,y) where...
        x is Easting in m (Alvin local grid)
        y is Northing in m (Alvin local grid)
    '''
    x = (lon - orglon) * mdeglon(orglat);
    y = (lat - orglat) * mdeglat(orglat);
    return (x,y)



def xy2ll(x, y, orglat, orglon):

    '''
    X/Y to Lat/Lon
    Converts Alvin XYs to Lat/Lon (WGS84) using a Mercator projection.

    Args:
      x (float): Easting in m (Alvin local grid)
      x (float): Northing in m (Alvin local grid)
      orglat (float): Latitude of origin location
      orglon (float): Longitude of origin location

    Returns:
      tuple: (lat,lon) 
    '''
    lon = x/mdeglon(orglat) + orglon
    lat = y/mdeglat(orglat) + orglat

    return (lat, lon)


# Vectorize
vxy2ll = np.vectorize(xy2ll)
vll2xy = np.vectorize(ll2xy)