Defining the Location of GAD Objects

Geotechnical Assets

As described in CS641, the extents of Geotechnical Assets should be defined by:

Points of zero height between Geotechnical Assets of different types.
Bridges and underpasses.
Service provider area boundaries.
Significant changes in geology (as shown on the 1:50,000 British Geological Survey map, or observed).
Significant changes in earthwork fill materials (as shown on as-built drawings, or observed).

During creation of a Geotechnical Asset you will be asked to define the location of the Start and End of the Asset using easting and northing co-ordinates aligned with the Ordnance Survey National Grid (OSGB). Co-ordinates can be input directly, or by selecting a point on the map.

Both the start and end location must be selected on the same side of the Network. Selecting to select both points on the same side of the Network will cause the system to fail to link both locations.

When selected or entered, the start location will show on the map as a green cross . The end location will show as a green plus sign .

A description can also be added to help define co-ordinates in relation to a reference points which can be visually observed in-situ (e.g. mile posts). The co-ordinates can then later be defined from the information about the reference point, the direct distance from it and the chainage distance (both in metres).

You will also define whether the Asset is 'Off-network'. Off network objects are not related to the current road network (or cannot currently be related to the network pending a refresh), but still need to be recorded in the system.

Off network Assets will not follow the alignment of the road and will not snap to Network sections. The Asset extents will be a straight line between your selected start and end locations.

Classifying Assets as 'Off-Network' will limit the analysis capabilities of the system for that Asset. It should only be selected in rare and exceptional circumstances and you will be prompted to record the reason.

'Snapping' to Network

The NH road Network is represented digitally on the system by the IAM-IS network model. This splits the Network into discrete, uniquely identifiable segments, which can be viewed and searched from the Map.

For 'On-Network' Assets, the start and end locations of an Asset (as well as any intermediate locations) must be linked to one of these Network segments. The linked location is used for a variety of reporting and analysis purposes within the system, for example to calculate the length of the Asset along the carriageway.

The link is formed automatically by clicking the Snap To Network button on the Command Bar, after inputting the co-ordinates.

When snapped, the start snapped location will show as a red cross . The end snapped location will show as a red plus sign .

The Asset location (defined by the co-ordinates previously input) is displayed on the map, alongside the suggested 'snapped' point on the Network. Click Next on the command bar to confirm.

Each location can only be snapped to one segment. Where several segments are close together, a list of possible snapped points is presented (one for each possible segment), for you to select the correct one. This would occur for example near a junction, where an Asset could be associated with either the main carriageway or the slip road.

Finally click Link Locations on the command bar and an offset representation of the asset will be shown on the map.

A number of validation checks are undertaken at this point to make sure that the asset does not cross over a road section including slip roads i.e. the Asset follows the 'kerb-line'.

Locations which are more than 200m from the nearest segment cannot be snapped to the network.
The IAM-IS network model will be refreshed intermittently, but will not always be fully up to date. Where the road layout has recently been changed, it may not be possible to snap an asset location correctly until the IAM-IS model is refreshed. In such cases, the asset should be temporarily recorded as 'off-network' and updated once the model has been refreshed.

Condition and Inventory Items

During creation of a Condition or Inventory Item you will be asked to define its location.

You can locate the item by defining its start and end points in the same way as for Geotechnical Assets. Where possible you should enter the start and end locations in the same direction as the Asset chainage.

When selected or entered, the start location will show on the map as a green cross . The end location will show as a green plus sign .

As part of the process you will be asked to optionally create a slope geometry at the start and end of the item.

Alternatively, you can fully define the co-ordinate of the mid-point, and then specify the objects length.

If creating a mid-point item you will be asked to optionally create a slope geometry at the item mid-point.

When selected or entered, the mid-point location will show on the map as a green cross .

Locating an object by its mid-point is primarily intended for short features (less than approx. 20m) where recording the start and end could lead to a significantly inaccurate length due to the GPS accuracy of the two points.

'Snapping' to Asset

A three-dimensional Geotechnical Asset is represented on the system as a linear object i.e. a line on the map.

The location of Items must be linked to a point along the Geotechnical Asset, in a similar way that Geotechnical Assets must be linked to the road network model.

The link is formed automatically by clicking the Snap To Asset button on the Command Bar, after inputting the co-ordinates.

When snapped, the start and mid-point snapped locations will show as a red cross . The end snapped location will show as a red plus sign .

After snapping each location you will be prompted to choose an IAM-IS section to associate each point with from a summary grid. The closest section to your selected point will be the default section and highlighted in orange on the map. To change the section select a different option from the grid.

Once all locations have been snapped and sections selected, click Link Locations on the command bar and an offset representation of the asset will be shown on the map.

If creating a mid-point item, enter the length of the item and then click Link Locations.

Click Finish Locating to complete the locating process and be prompted to enter the item's details.

Locating items outside or towards the end of the extents of parent objects

The extents of an item must lie fully within the extents of its parent object (an asset or inventory item). Therefore when defining an items extents there are the following scenarios to consider:

Start/ end point outside of extents - If you select a point outside the extents of its parent, the point will snap to the end of the extents. The picture below shows an example of the start point of an item located outside the extent of an Asset and snapped to the start of the Asset extents:
Mid-point outside of extents - If the mid-point of an item is located outside the extents of its parent, the mid-point will be snapped to the nearest edge of the parent extents. The length of the item will be the entered length starting from the edge of the parent extents. The picture below shows a mid-point located outside the extents of an Asset extents (purple line) and the item extents (shown as offset in green) starting from the edge of the Asset extents:
Mid-point located less than half the entered length from the start or end extents - If the mid-point of an item is located less than half the entered item length from the start or end of the parent extents, the mid-point of an item will snap to the extents as expected. The item extents will start at the edge of the parent extents and extents length will be the entered length. In the example shown below, the mid-point is located 15m from the start of the Asset and has an entered length of 80m. As the item is less than half the entered length from the start, the mid-point snaps in the expected location and the item extents is 80m from the start of the Asset:
Entered length of mid-point item larger than length of parent object - If a mid-point item has an entered length greater than the length of its parent's extents, the item extents will show as the same length as its parent. The item length will still show as its entered length in the item's Details page, but the extents will show as the length of its parent.

Condition and Inventory Sets

The location and extents of Condition and Inventory Sets are determined automatically by the system, based upon their constituent Items.

Intermediate Slope Geometries

During creation of an intermediate Slope Geometry you will be asked to define its location along the Asset.

This is done in the same way as for Condition and Inventory Items described above, although only a single point location is defined (no length input is required). Slope Geometries can also be located during the locating of items, see here for details of creating Slope Geometries. The Slope Geometry will be located at the start or end of the extents of the item if created for a start and end item. If you choose to create a slope geometry for a mid-point item, it will be located at the snapped location of the mid-point.