This module provides helper functions for contour plotting on a map background, when data points are provided with coordinates (x,y), values and name. Depends on matplotlib, numpy and PIL.
plot_contours(filename, points, options)¶
Create a contour plot image based on data points. points is a list object containing tupples of the form (x, y, v, name) where x,y the coordinates of each point, v a floating point value or any non-arithmetic value (such as None or NaN) if the value is unknown. name is a string containing the point name for labeling. filename is the full path (containing directory) of the image file that will be written. options is a dictionary like object holding several options for the contours creation process. Options are explained bellow:
- contours_font_size, see matplotlib documentation.
- labels_format, e.g. ‘%f’, see matplotlib documentation.
- draw_contours, True to draw contours.
- color_map, e.g. ‘winter_r’, ‘hsv’, ‘hot’ etc, see matplotlib documentation.
- labels_font_size, see matplotlib documentation.
- text_color, e.g. ‘black’, see matplotlib documentation.
- contours_color, e.g. ‘red’, see matplotlib documentation.
- draw_labels, True to draw labels.
- markers_color, e.g. ‘green’, see matplotlib documentation.
- markers_style, ‘+’, ‘*’ etc. see matplotlib documentation.
- draw_markers, True to draw markers.
- granularity, the detail of the contour grid. Start from a value of 30 increasing for much detail. Over 100 maybe is useless. Do not drop under 5.
- chart_bounds_bl_x, the bottom left abscissa of the map.
- chart_bounds_bl_y, the bottom left ordinate of the map.
- chart_bounds_tr_x, the top right abscissa of the map.
- chart_bounds_tr_y, the top right ordinate of the map.
- chart_bounds_srid, the referense system for the coordinates, use a conformal projection such as UTM or spherical mercator to have identical scales on x and y, e.g. 2100 for GRRS-87.
- compose_background, set to True to overlay contours on a map background. The composition is realized with the PIL module.
- background_image, the filename (w/o directory) of the background for composition.
- mask_image, an optional image containing mixing values as alpha values, when composition method is ‘composite’. See PIL documentation.
- compose_method, e.g. ‘add’, ‘multiply’, ‘blend’, ‘composite’, see PIL documentation.
- swap_bg_fg, Swap the bacground and foreground (contours) image order. It has effect on some methods such as ‘composite’, ‘blend’, ‘add’, ‘subtract’.
- compose_alpha, the mixing ration between bg and fg, has mean only for ‘blend’ method. It is used also in ‘add’ and ‘subtract’ as scale parameter.
- compose_offset, an offset parameter for ‘add’ and ‘subtract method’.
- backgrounds_path, the path of the directory holding bacground and mask images.
- chart_large_dimension, an integer tha specifies the large dimension of the chart produced.
- boundary_distance_factor, the default value is 1. It specifies the size of the virtual boundary. If width, height are the dimensions of the displayed area, then the virtual boundary has a size of (1+2*fac)*width, (1+2*fac)*height. Factor values should be altered with caution.
- boundary_value, default value is 0. This is the value of the points on the virtual boundary. A value of 0 is ok for rainfall events.
- boundary_mode is an integer value, default is 0. If set to zero (0) then the boundary value specified by the boundary_value parameter is a constant number. If set to one (1) then the boundary_value is a factor to the mean value of all data points. Then the factor*mean_value is set to all data points on the boundary.