python - Rounding all coordinates in shapely?

Following on from How can I add points to a LineString in shapely?, I'm hitting a problem where floating point representations mean objects aren't precisely where I expect them be after they are moved using affinity.translate.

This would be fixed if there was a way of rounding all the coordinates to the nearest cm (or other insignificantly-small value).

Does this exist?

---

For what it's worth, I'm doing all my intersection and union operations first before the translation and that seems to be working.

Answer

Shapely and GEOS cannot reduce precision (floating-point precision problem) but you can use other functions as numpy.round() or round(),with the GeoJSON format.

For polygons

from shapely.geometry import shape, mapping
import numpy as np
# one polygon
print poly.wkt

POLYGON ((101.2200527190607 -114.6493019170767, 146.6225142079163 -114.4488495484725, 185.0301801801801 -114.2792792792793, 184.6581081081081 -217.7153153153153, 14.99324324324321 -218.4594594594595, 16.4815315315315 -115.0234234234234, 101.2200527190607 -114.6493019170767))
# convert to GeoJSON format
geojson = mapping(poly)
print geojson
{'type': 'Polygon', 'coordinates': (((101.2200527190607, -114.6493019170767), (146.6225142079163, -114.4488495484725), (185.0301801801801, -114.2792792792793), (184.6581081081081, -217.7153153153153), (14.99324324324321, -218.4594594594595), (16.4815315315315, -115.0234234234234), (101.2200527190607, -114.6493019170767)),)}
 geosjson['coordinates'] = np.round(np.array(geosjon['coordinates']),2)
 print geosjson
 {'type': 'Polygon', 'coordinates': array([[[ 101.22, -114.65],
    [ 146.62, -114.45],
    [ 185.03, -114.28],

    [ 184.66, -217.72],
    [  14.99, -218.46],
    [  16.48, -115.02],
    [ 101.22, -114.65]]])}
 print shape(geosjson)
 POLYGON ((101.22 -114.65, 146.62 -114.45, 185.03 -114.28, 184.66 -217.72, 14.99 -218.46, 16.48 -115.02, 101.22 -114.65))

If you don't want to use Numpy, you can adapt the function def _set_precision(coords, precision) of the geosjson-precision module

 def set_precision(coords, precision):
    result = []

    try:
        return round(coords, int(precision))
    except TypeError:
        for coord in coords:
            result.append(_set_precision(coord, precision))
    return result
 geojson = mapping(poly)
 geosjson['coordinates']= set_precision(geosjson['coordinates'], 2)
 print geosjson
 {'type': 'Polygon', 'coordinates': [[[101.22, -114.65], [146.62, -114.45], [185.03, -114.28], [184.66, -217.72], [14.99, -218.46], [16.48, -115.02], [101.22, -114.65]]]}

 print shape(geosjson)
 POLYGON ((101.22 -114.65, 146.62 -114.45, 185.03 -114.28, 184.66 -217.72, 14.99 -218.46, 16.48 -115.02, 101.22 -114.65))