Introduction
As discussed in https://navtechradar.atlassian.net/wiki/spaces/TUN/pages/789839905/Final+Steps#Carriageway-Stats there are fields that show the expected radar coverage for a section of carriageway, as well as the actual radar coverage for the section, pending a healthy radar connection.
This page covers when there are changes to the carriageway coverage status which can also highlight problems with the radar.
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This page covers carriageway section allocation to a radar and coverage.
Coverage is where we have radar coverage for all or parts of a carriageway so we can track vehicles.
Allocation is how we have allocated sections of a carriageway to radar for the sole purpose of gathering traffic statistics.
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Coverage
There are four elements which control coverage:
Range of the Radar
The range of the radar depends on the model deployed and is calculated by the Range Resolution x Range in Bins. In the example below, the range is displayed within the purple boundary and the Raw Data is displayed in bright green:
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Radar Contour Map
The radar processes raw data far beyond the carriageway area, and this data is superfluous. Therefore, by creating a Contour Area, you prevent the steaming of unnecessary data.
In the example below, the range of the radar is still within the purple boundary, however, a Contour Map has been created which limits the range of the radar to the area near the carriageway. The Raw Data from this Radar Contour Map can be seen in bright green:
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Exclusion Areas
An Exclusion Area is the equivalent of a black hole to the system; everything within its borders is completely ignored. This is useful to have at a junction, or roundabout, for example, to prevent a car waiting to pull out being classified as a Stopped Vehicle.
In the example below, the Exclusion Area is in bright yellow, and this further limits the radar coverage:
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Radar Group Allocation to a Carriageway
Finally, Radar Group allocation to a carriageway can effect the range of a radar. In the example below, which is within a tunnel with two bores, there are two Radar Groups; one for each of the single carriageways; one travelling eastwards, and the other westwards. Using two different radar groups, the eastwards radar will not report back any data from the westward carriageway and vice-versa:
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Allocation
There are two sensor allocation modes:
Nearest
This is the default mode. The section closest to a radar is allocated to only that radar for purposes of gathering traffic stats.
We can lose a section if a radar fails but we might not lose coverage because another radar covers the section in question. So this means we can always have overlapping tracking coverage but we can't have the concept of overlapping with traffic stats gathering when using nearest because its always 1 section to 1 radar. In the image below, the radar with a black boundary has failed, but the range of the radar either side of it will have overlapping tracking coverage, but there will not be tracking stats within the black boundary:
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All in Range
In this mode the radar will gather traffic stats from all sections within range of the radar. This means where radar have overlapping coverage then we will gather duplicate statistics for sections covered by more than one radar.
The implications for a radar failure are slightly different for coverage and section allocation.
Section to Radar Allocation
Your allocation images can be used to explain how section - radar allocation works
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Here is the map showing a carriageway with a healthy carriageway coverage status for a section.
The Normal Coverage and Current Coverage of the radar for the selected section 19 (which is well within the range of the radar) is showing 100%:
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Peripheral Coverage
When sections of the carriageway are situated towards the edge of the radar range, then the coverage may be reduced. Section 15 is near the edge of the radar boundary, and it shows a Normal and Current Coverage of 99.3%:
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Coverage Out Of Range
Section 14 is just over the boundary of the radar range and so the normal and current coverage is greatly reduced - both at 0.9%:
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Section 13 is out of range of the radar, and therefore not allocated to it. It is therefore expected that the normal and current coverage are at 0.0%.
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Exclusion Area
There are other reasons why coverage is not as high as you’d expect; in this scenario, an exclusion area, highlighted in yellow, has been placed within halfway of Section 19, and this excludes any radar data returning from this area, so the Normal and Current Coverage are at 47.4%:
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Unhealthy Radar
If the radar status is unhealthy then the radar coverage falls; in the example below it is expected to be at 100% but the Current Coverage is showing as 0.0%:
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The coverage status change is reflected in the ICD-001 Carriageway Statistics Report.
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