A `Shapes` structure is a collection of shapes extracted from an image.
The fields `nrow`

and `ncol`

are the dimensions of the image.
The field `interpolation`

is the convention used to extract level
lines. Currently, the valid values are 0 (module `flst`

) and 1 (module
`flst_bilinear`

).

The elements are stored consecutively in the array `the_shapes`

of size
`nb_shapes`

. By convention, the shape at index 0 is the root of the
tree.

The field `smallest_shape`

is an array of size
`nrow`

×`ncol`

giving for each pixel the smallest shape in
the tree that contains it. By going upward in the tree, it is possible to know
all the shapes containing a given pixel.

mw 2004-05-05