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Snap to Network

Available in real-time and big data analytics.

The Snap to Network tool updates point geometry to align with a polyline network. The distance to search from point features must be specified. The tool aligns, or snaps, point features to network elements within that distance.

The Track ID and Start time options must be specified on the input dataset, as the track-based sequential and directional nature of observations is used to snap the features to the correct network line feature.

The Snap to Network tool has two input datasets. The target dataset is the point features dataset of observations that have both Track ID and Start time options. The join dataset is a polyline dataset representing a network. This polyline dataset has three required fields to function with the Snap to Network tool. The Usage notes section provides more details.

Examples

The following are example use cases for the tool:

  • A transportation organization is monitoring vehicles equipped with automatic vehicle location (AVL) tracking devices. The Snap to Network tool can be used to snap observations to a road network to improve the accuracy of the AVL GPS observations.

  • A city is monitoring snowplow operations and wants to better understand vehicle movement. The Snap to Network tool can be used to snap observations to the city's road network. The LineID attribute field can be used in an attribute join to enrich vehicle observations with the road segment attribute information for the road the vehicle is traveling along.

Usage notes

Note the following when working with the tool:

  • The schema of the layer for the polyline features network must contain proper values in the following three fields:

    • OBJECTID or FID

    • F_AUTOMOBI or F_AUTOMOBILES

    • T_AUTOMOBI or T_AUTOMOBILES

  • The OBJECTID or FID field provided must contain a unique integer (numeric) value for each polyline feature. If the OBJECTID or FID field is provided as a float, it is converted to an integer.

  • The F_AUTOMOBI / F_AUTOMOBILES and T_AUTOMOBI / T_AUTOMOBILES fields indicate the driving direction relative to the digitizing direction of the polyline features. The F_AUTOMOBI / F_AUTOMOBILES and T_AUTOMOBI / T_AUTOMOBILES fields should be string fields with a value of either Y or N. If you have fields with these values but with different field names, you can use the Calculate Fields or Map Fields tool to change or generate a copy of these fields with the required names.

    • If the driving direction is against the digitizing direction, F_AUTOMOBI / F_AUTOMOBILES = Y and T_AUTOMOBI / T_AUTOMOBILES = N.

    • If the driving direction is the same as the digitizing direction, F_AUTOMOBI / F_AUTOMOBILES = N and T_AUTOMOBI / T_AUTOMOBILES = Y.

    • If the street segment is a two-way street, F_AUTOMOBI / F_AUTOMOBILES = N and T_AUTOMOBI / T_AUTOMOBILES = N.

  • The Split distance, Split duration, and Heading parameters are optional.

  • Target features missing geometry, track ID values, or start time values are discarded from the snapped features.

  • Network features missing geometry are not considered.

  • Point features don't snap to network polyline segments with a value of Y for both F_AUTOMOBI / F_AUTOMOBILES and T_AUTOMOBI / T_AUTOMOBILES fields because they are treated as a closed segment.

  • This tool requires geometry.

  • When the Prevent wrong-way snapping on one-way roads parameter is checked (default), a point feature is not snapped to a one-way road segment if it is traveling opposite the permitted direction of travel. To allow a point feature to be snapped to the best segment, even when it is traveling opposite the permitted direction of travel on a one-way road, leave this parameter unchecked.

Parameters

The following table describes the parameters for the tool:

Parameter

Description

Data type

Input layer

The point features to snap to the network based on user-defined parameter values.

This dataset must have Track ID and Start Time key fields defined.

Point Features

Network layer

The polyline features representing a network to which the input point features are snapped.

The layer must have the following three fields:

  • OBJECTID or FID

  • F_AUTOMOBI / F_AUTOMOBILES

  • T_AUTOMOBI / T_AUTOMOBILES

The F_AUTOMOBI / F_AUTOMOBILES and T_AUTOMOBI / T_AUTOMOBILES fields indicate the driving direction relative to the digitizing direction of the polyline features. The F_AUTOMOBI and T_AUTOMOBILES fields should be string fields with a value of either Y or N. If you have fields with these values but with different names, you can use the Calculate Fields or Map Fields tool to change or generate a copy of these fields with the required names.

  • If the driving direction is against the digitizing direction, F_AUTOMOBI / F_AUTOMOBILES = Y and T_AUTOMOBI / T_AUTOMOBILES = N.

  • If the driving direction is the same as the digitizing direction, F_AUTOMOBI / F_AUTOMOBILES = N and T_AUTOMOBI / T_AUTOMOBILES = Y.

  • If the street segment is a two-way street, F_AUTOMOBI / F_AUTOMOBILES = N and T_AUTOMOBI / T_AUTOMOBILES = N.

Polyline Features

Search distance

The distance to search from each point feature for network features that the point features can snap to.

String

Track ID fields

The fields that uniquely identify observations. If the track ID is identified in the input dataset, it is automatically picked up.

If a track ID has not been specified for the input dataset, this parameter must be used to identify the Track ID fields that uniquely identify observations.

String

Split duration

(Optional)

The amount of time between observations that, if exceeded, breaks the processing out to a separate track.

String

Split distance

(Optional)

The distance between observations that, if exceeded, breaks the processing out to a separate track.

String

Heading

(Optional)

If the input features have a heading field with values, the field can be specified in this parameter to improve how accurate the points snap to the network.

The field specified for the heading must be a numeric field.

String

Join fields

Choose fields from the network schema to add to the target features.

For example, if a join field of STREET_NAME is chosen, the output schema has the field STREET_NAME added. If a point is snapped to a street named Main Street, the value for this field is also Main Street.

String

Feature handling

Used to specify how the Snap to Network tool should handle features that are not snapped to a network feature.

You can retain features that snap to the network, or all features including those that don't snap to the network.

If a feature is not snapped successfully, the original geometry is retained and fields that the Snap to Network tool should have populated contain a null value.

The options are: Retain only features that are snapped to the network or Retain all features.

Boolean

Prevent wrong-way snapping on one-way roads

When this parameter is checked, a point feature is not snapped to a one-way road segment if it is traveling opposite the segment's permitted direction of travel. The default is checked.

When this parameter is unchecked, a point feature is snapped to the best segment even if it is traveling opposite the permitted direction of travel on a one-way road segment.

Boolean

Output layer

The output layer contains the following attributes appended to the original attributes for each feature. Any join fields specified are also added to the output layer.

Field name

Description

Field type

OrigX

The original x-coordinate of the point.

Float64

OrigY

The original y-coordinate of the point.

Float64

LineID

The OBJECTID or FID of the network polyline feature that the point feature was snapped to.

Float64

FractionAlong

The percentage fraction along this polyline on which the point feature was snapped.

Float64

DistanceToLine

The distance from the original feature to the point along the polyline where it was snapped.

Float64

SnapScore

The relative estimated accuracy of the snap operation.

Float64

HeadingOriginal

The heading as calculated by the original position of the point (and its immediate prior point).

Float64

HeadingSnapped

The heading as calculated by the snapped position of the point (and its immediate prior snapped point).

Float64