Polyline Conversion

A guide for bidirectional V1/V2 conversion of polyline annotations.

Data Structure

V1 Structure

# annotations
{
    "id": "polyline_1",
    "tool": "polyline",
    "isLocked": False,
    "isVisible": True,
    "isValid": True,
    "classification": {
        "class": "road_line",
        "type": "dashed"
    },
    "label": ["road_line"]
}

# annotationsData
{
    "id": "polyline_1",
    "coordinate": [
        {"x": 100, "y": 200, "id": "pt_1"},
        {"x": 150, "y": 250, "id": "pt_2"},
        {"x": 200, "y": 200, "id": "pt_3"}
    ]
}

V2 Structure

{
    "id": "polyline_1",
    "classification": "road_line",
    "attrs": [
        {"name": "type", "value": "dashed"}
    ],
    "data": [[100, 200], [150, 250], [200, 200]]
}

Conversion Rules

V1 → V2

V1 Field	V2 Field
coordinate[{x, y, id}]	data[[x, y], ...]
classification.class	classification
classification.{other}	attrs[{name, value}]

V2 → V1

V2 Field	V1 Field
data[[x, y], ...]	coordinate[{x, y, id}]
classification	classification.class
attrs[{name, value}]	classification.{name: value}

note

During V2→V1 conversion, point IDs are automatically generated as pt_0, pt_1, ...

Usage Examples

Basic Conversion

from synapse_sdk.utils.converters.dm import convert_v1_to_v2, convert_v2_to_v1

# V1 polyline data
v1_data = {
    "annotations": {
        "image_1": [
            {
                "id": "Line123abc",
                "tool": "polyline",
                "classification": {"class": "road_line", "type": "dashed"}
            }
        ]
    },
    "annotationsData": {
        "image_1": [
            {
                "id": "Line123abc",
                "coordinate": [
                    {"x": 100, "y": 200, "id": "pt_1"},
                    {"x": 150, "y": 250, "id": "pt_2"},
                    {"x": 200, "y": 200, "id": "pt_3"}
                ]
            }
        ]
    }
}

# Convert to V2
result = convert_v1_to_v2(v1_data)
annotation_data = result["annotation_data"]

# Check V2 result
polyline = annotation_data["images"][0]["polyline"][0]
print(polyline["data"])  # [[100, 200], [150, 250], [200, 200]]
print(polyline["classification"])  # "road_line"
print(polyline["attrs"])  # [{"name": "type", "value": "dashed"}]

Roundtrip Verification

def verify_polyline_roundtrip(v1_original):
    """Verify polyline roundtrip"""
    # V1 → V2 → V1
    v2_result = convert_v1_to_v2(v1_original)
    v1_restored = convert_v2_to_v1(v2_result)

    # Compare coordinates
    orig_coord = v1_original["annotationsData"]["image_1"][0]["coordinate"]
    rest_coord = v1_restored["annotationsData"]["image_1"][0]["coordinate"]

    assert len(orig_coord) == len(rest_coord)
    for i, (orig, rest) in enumerate(zip(orig_coord, rest_coord)):
        assert orig["x"] == rest["x"]
        assert orig["y"] == rest["y"]

    print("Polyline roundtrip verification successful")

verify_polyline_roundtrip(v1_data)

Difference from Polygon

Property	Polyline	Polygon
Shape closure	Open shape	Closed shape
Minimum points	2	3
Purpose	Lines, paths	Areas