flexpolyline

FlexPolyline

This is a python implementation of the Flexible Polyline format.

The polyline encoding is a lossy compressed representation of a list of coordinate pairs or coordinate triples. It achieves that by:

1. Reducing the decimal digits of each value.
2. Encoding only the offset from the previous point.
3. Using variable length for each coordinate delta.
4. Using 64 URL-safe characters to display the result.

Install

pip install flexpolyline

Usage

Encoding

encode(iterable, precision=5, third_dim=ABSENT, third_dim_precision=0)

Encodes a list (or iterator) of coordinates to the corresponding string representation. See the optional parameters below for further customization. Coordinate order is (lat, lng[, third_dim]).

**Optional parameters**

* `precision` - Defines how many decimal digits to round latitude and longitude to (ranges from `0` to `15`).
* `third_dim` - Defines the type of the third dimension when present. Possible values are defined in the module: `ALTITUDE`, `LEVEL`, `ELEVATION`, `CUSTOM1` and `CUSTOM2`. The last two values can be used in case your third dimension has a user defined meaning.
* `third_dim_precision` - Defines how many decimal digits to round the third dimension to (ranges from `0` to `15`). This parameter is ignored when `third_dim` is `ABSENT` (default).


#### `dict_encode(iterable, precision=5, third_dim=ABSENT, third_dim_precision=0)`

Similar to the `encode` function, but accepts a list (or iterator) of dictionaries instead. Required keys are `"lat"` and `"lng"`. If `third_dim` is set, the corresponding key is expected `"alt"`, `"elv"`, `"lvl"`, `"cst1"` or `"cst2"`. 


#### Examples

Following is a simple example encoding a 2D poyline with 5 decimal digits of precision:

```python
import flexpolyline as fp

example = [
    (50.1022829, 8.6982122),
    (50.1020076, 8.6956695),
    (50.1006313, 8.6914960),
    (50.0987800, 8.6875156),
]

print(fp.encode(example))

Output: BFoz5xJ67i1B1B7PzIhaxL7Y.

Another example for the 3D case with altitude as the third coordinate:

example = [
    (50.1022829, 8.6982122, 10),
    (50.1020076, 8.6956695, 20),
    (50.1006313, 8.6914960, 30),
    (50.0987800, 8.6875156, 40),
]

print(fp.encode(example, third_dim=flexpolyline.ALTITUDE))

Output: BlBoz5xJ67i1BU1B7PUzIhaUxL7YU

Decoding

decode(encoded_string)

Decodes the passed encoded string and returns a list of tuples (lat, lng[, third_dim]).

iter_decode(encoded_string)

Similar to decode but returns an iterator instead.

dict_decode(encoded_string)

Similar to decode but returns a list of dictionaries instead. The keys "lat" and "lng" are always present, while the third dimension key depends on the type of third dimension encoded. It can be one of the following: "alt", "elv", "lvl", "cst1" or "cst2".

iter_dict_decode(encoded_string)

Similar to dict_decode but returns an iterator instead.

get_third_dimension(encoded_string)

Returns the value corresponding to the third dimension encoded in the string. Possible values defined in the module are: ABSENT, ALTITUDE, LEVEL, ELEVATION, CUSTOM1 and CUSTOM2

Examples

Example of decoding of a 2D polyline:

import flexpolyline as fp

print(fp.decode("BFoz5xJ67i1B1B7PzIhaxL7Y"))

Output:

[
    (50.10228, 8.69821),
    (50.10201, 8.69567),
    (50.10063, 8.69150),
    (50.09878, 8.68752)
]

Example of decoding dicts from a 3D polyline:

import flexpolyline as fp

print(fp.dict_decode("BlBoz5xJ67i1BU1B7PUzIhaUxL7YU"))

Output:

[
    {'lat': 50.10228, 'lng': 8.69821, 'alt': 10},
    {'lat': 50.10201, 'lng': 8.69567, 'alt': 20},
    {'lat': 50.10063, 'lng': 8.69150, 'alt': 30},
    {'lat': 50.09878, 'lng': 8.68752, 'alt': 40}
]