Source code for climada.util.scalebar_plot

This file is part of CLIMADA.

Copyright (C) 2017 ETH Zurich, CLIMADA contributors listed in AUTHORS.

CLIMADA is free software: you can redistribute it and/or modify it under the
terms of the GNU General Public License as published by the Free
Software Foundation, version 3.

CLIMADA is distributed in the hope that it will be useful, but WITHOUT ANY
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PARTICULAR PURPOSE.  See the GNU General Public License for more details.

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with CLIMADA. If not, see <>.


Function to plot scale bar. Source code by mephistolotl from:

import numpy as np
import as ccrs
import cartopy.geodesic as cgeo

def _axes_to_lonlat(ax, coords):
    """(lon, lat) from axes coordinates."""
    display = ax.transAxes.transform(coords)
    data = ax.transData.inverted().transform(display)
    lonlat = ccrs.PlateCarree().transform_point(*data, ax.projection)

    return lonlat

def _upper_bound(start, direction, distance, dist_func):
    """A point farther than distance from start, in the given direction.

    It doesn't matter which coordinate system start is given in, as long
    as dist_func takes points in that coordinate system.

    start :
        Starting point for the line.
    direction :
        Nonzero (2, 1)-shaped array, a direction vector.
    distance :
        Positive distance to go past.
    dist_func :
        A two-argument function which returns distance.

    coords : a (2, 1)-shaped NumPy array
        Coordinates of a point.
    if distance <= 0:
        raise ValueError(f"Minimum distance is not positive: {distance}")

    if np.linalg.norm(direction) == 0:
        raise ValueError("Direction vector must not be zero.")

    # Exponential search until the distance between start and end is
    # greater than the given limit.
    length = 0.1
    end = start + length * direction

    while dist_func(start, end) < distance:
        length *= 2
        end = start + length * direction

    return end

def _distance_along_line(start, end, distance, dist_func, tol):
    """Point at a distance from start on the segment  from start to end.

    It doesn't matter which coordinate system start is given in, as long
    as dist_func takes points in that coordinate system.

    start :
        Starting point for the line.
    end :
        Outer bound on point's location.
    distance :
        Positive distance to travel.
    dist_func :
        Two-argument function which returns distance.
    tol :
        Relative error in distance to allow.

    Coordinates of a point (a (2, 1)-shaped NumPy array).
    initial_distance = dist_func(start, end)
    if initial_distance < distance:
        raise ValueError(f"End is closer to start ({initial_distance}) than "
                         f"given distance ({distance}).")

    if tol <= 0:
        raise ValueError(f"Tolerance is not positive: {tol}")

    # Binary search for a point at the given distance.
    left = start
    right = end

    while not np.isclose(dist_func(start, right), distance, rtol=tol):
        midpoint = (left + right) / 2

        # If midpoint is too close, search in second half.
        if dist_func(start, midpoint) < distance:
            left = midpoint
        # Otherwise the midpoint is too far, so search in first half.
            right = midpoint

    return right

def _point_along_line(ax, start, distance, angle=0, tol=0.01):
    """Point at a given distance from start at a given angle.

    ax :
        CartoPy axes.
    start :
        Starting point for the line in axes coordinates.
    distance :
        Positive physical distance to travel.
    angle :
        Anti-clockwise angle for the bar, in radians. Default: 0
    tol :
        Relative error in distance to allow. Default: 0.01

    Coordinates of a point (a (2, 1)-shaped NumPy array).
    # Direction vector of the line in axes coordinates.
    direction = np.array([np.cos(angle), np.sin(angle)])

    geodesic = cgeo.Geodesic()

    # Physical distance between points.
    def dist_func(a_axes, b_axes):
        a_phys = _axes_to_lonlat(ax, a_axes)
        b_phys = _axes_to_lonlat(ax, b_axes)

        # Geodesic().inverse returns a NumPy MemoryView like [[distance,
        # start azimuth, end azimuth]].
        return geodesic.inverse(a_phys, b_phys).base[0, 0]

    end = _upper_bound(start, direction, distance, dist_func)

    return _distance_along_line(start, end, distance, dist_func, tol)

[docs]def scale_bar(ax, location, length, metres_per_unit=1000, unit_name='km', tol=0.01, angle=0, color='black', linewidth=3, text_offset=0.005, ha='center', va='bottom', plot_kwargs=None, text_kwargs=None, **kwargs): """Add a scale bar to CartoPy axes. For angles between 0 and 90 the text and line may be plotted at slightly different angles for unknown reasons. To work around this, override the 'rotation' keyword argument with text_kwargs. Parameters ---------- ax : CartoPy axes. location : Position of left-side of bar in axes coordinates. length : Geodesic length of the scale bar. metres_per_unit : Number of metres in the given unit. Default: 1000 unit_name : Name of the given unit. Default: 'km' tol : Allowed relative error in length of bar. Default: 0.01 angle : Anti-clockwise rotation of the bar. color : Color of the bar and text. Default: 'black' linewidth : Same argument as for plot. text_offset : Perpendicular offset for text in axes coordinates. Default: 0.005 ha : Horizontal alignment. Default: 'center' va : Vertical alignment. Default: 'bottom' plot_kwargs : Keyword arguments for plot, overridden by `**kwargs`. text_kwargs : Keyword arguments for text, overridden by `**kwargs`. kwargs : Keyword arguments for both plot and text. """ # Setup kwargs, update plot_kwargs and text_kwargs. if plot_kwargs is None: plot_kwargs = {} if text_kwargs is None: text_kwargs = {} plot_kwargs = {'linewidth': linewidth, 'color': color, **plot_kwargs, **kwargs} text_kwargs = {'ha': ha, 'va': va, 'rotation': angle, 'color': color, **text_kwargs, **kwargs} # Convert all units and types. location = np.asarray(location) # For vector addition. length_metres = length * metres_per_unit angle_rad = angle * np.pi / 180 # End-point of bar. end = _point_along_line(ax, location, length_metres, angle=angle_rad, tol=tol) # Coordinates are currently in axes coordinates, so use transAxes to # put into data coordinates. *zip(a, b) produces a list of x-coords, # then a list of y-coords. ax.plot(*zip(location, end), transform=ax.transAxes, **plot_kwargs) # Push text away from bar in the perpendicular direction. midpoint = (location + end) / 2 offset = text_offset * np.array([-np.sin(angle_rad), np.cos(angle_rad)]) text_location = midpoint + offset # 'rotation' keyword argument is in text_kwargs. ax.text(*text_location, f"{length} {unit_name}", rotation_mode='anchor', transform=ax.transAxes, **text_kwargs)