mask

mask(fs, area, missing=False)

For each field in fs creates a field containing 0 or 1 values according to whether a grid point is inside (1) or outside (0) the area. An additional named argument, missing set to True will change the behaviour so that points outside the area will become missing values and points inside the area retain their original value.

Parameters

  • fs (Fieldset) – input fieldset

  • area (list) – area as [N, W, S, E]

  • missing (bool) – set to True to change the behaviour as described above. New in Metview version 5.13.0.

Return type

Fieldset

Example

Non-rectangular masks, and even convex masks can be created by using the operators and, or and not. To create the following mask:

../../_images/mask_1.png

first decompose it into basic rectangles:

../../_images/mask_2.png

then create a mask for each of them and use and and or to compose the desired mask like this:

import metview as mv

# Define basic rectangles
a = [50,-120,10,-30]
b = [20,20,50,10]
c = [50,50,40,100]
d = [35,-60,-40,100]

# The field defining the grids
f = mv.read(path_to_your_grib_file)

# First compute the union of a,c and d
m = mv.mask(f,a) or mv.mask(f,d) or mv.mask(f,c)

# Then remove b
m = m and not mv.mask(f,b)

Note

See also rmask(), poly_mask(), bitmap() and nobitmap().

mask(gpt, area)

Creates a Geopoints containing values of 0 or 1 according to whether they are inside (1) or outside (0) the area.

Parameters

  • gpt (Geopoints) – input geopoints

  • area (list) – area as [N, W, S, E]

Return type

Geopoints

Points with missing latitudes or longitudes are considered to be outside any area. See the documentation for the fieldset version of this function to see how to compose more complex regions than a simple rectangular area.

Notebooks using metview.mask

thumbnail

Slicing and dicing GRIB data