Thread: Cl

speedcam_maxdistance_from_road is used to ignore a speed camera alert if the camera is located farther away than the selected distance when passing it.

This parameter is important, for example, when driving on an expressway alongside a secondary road with a speed limit of 45 mph, while the expressway itself has a speed limit of 80 mph.

If a speed camera installed on the secondary road, configured to detect speeding above 45 mph regardless of direction, is located less than 10 metres from the expressway, iGO will issue a speeding alert on the expressway whenever you exceed 45 mph, even though you are well below the legal speed limit of 80 mph.

When a speed camera is located at the intersection of two crossing roads, and is therefore less than 10m from both roads, the correct use of directional mode will determine whether the camera is announced and whether the correct speed limit is applied.

For example, consider a speed camera located on a secondary road crossing over an expressway on a bridge. If the camera is intended to monitor traffic on the expressway, it should be configured with a speed limit of 80 mph and oriented in the direction of the expressway. If it is intended to monitor traffic on the secondary road, its orientation should be offset by 90 degrees and its speed limit set to 45 mph.

What remains to be verified in this example is whether a camera located on the bridge, configured and oriented to monitor the expressway, but positioned more than 10m from the expressway while still being located on the secondary road, will ultimately be announced by iGO or ignored.


It is therefore preferable not to tamper with this parameter, as its default value represents a reasonable compromise that works in most cases.

The same applies to speedcam_max_angle, which some people unnecessarily increase. Instead, it would be sufficient to adjust the directional angle of the few affected speed cameras to improve detection. Alternatively, problematic speed cameras could simply be cloned, assigning each clone the most appropriate angle and placing them opposite each other at the beginning of each curve, with each one oriented according to the direction of the road.
It should be noted that a value of 20° for this parameter already represents a lateral distance of 200 m from the intended direction at a distance of 1 km, which is more than sufficient for a speed camera positioned less than 10 m away.

It is also important to be aware of a certain reality: a speed camera positioned 10 m from the road with a detection angle of 20° will be only 27.5 m away from you when it leaves the visibility cone. In that case, the alert will have sounded long before that point—or, visually, you would have to be extremely short-sighted not to see it.

speedcam_snap_distance literally means "speed camera snap distance." Its value may indicate that, below the selected distance between the speed camera and the vehicle, the camera will no longer be announced because it is considered too close to have any meaningful influence on the driver's behavior, taking reaction time and braking distance into account.

There are four main parameters in sys.txt that affect speed camera detection:

speedcam_snap_distance=50 ;; Speed camera snap distance
speedcam_maxdistance_from_road=10 ;; Maximum distance from the road (route)
speedcam_max_angle=28 ;; Visibility cone = 2 * max_angle
speedcam_max_lookahead=500 ;; (1000)

One could say that speedcam_max_angle would represent the field of view, while speedcam_max_lookahead represents the maximum hyperopia and speedcam_snap_distance the minimum myopia at which a text is no longer readable, speedcam_max_angle.

Excessive or inappropriate modification of these values can interfere with predictive detection and the operation of other alert parameters. The most obvious example would be reducing speedcam_max_lookahead to 100 m when we know that laser speed cameras can detect vehicles from more than 1,000 m away.



In iGO, min_frc is most likely related to FRC = Functional Road Class.

FRC is a hierarchical classification of roads: motorways, expressways, main roads, secondary roads, local streets, etc. Whether a higher or lower numerical value represents a higher road class depends on the mapping system being used, so caution is needed when interpreting the exact numerical value.

The min_ prefix generally suggests “minimum FRC class” or “minimum FRC.”

In the context of speed cameras, navigation, or route searching, min_frc could therefore be used to define the minimum road class to be taken into account.

In the case of alerts in particular, one might want them to apply only to certain types of roads. This parameter appears to be mainly present in [speedcam_category:3], which defines section speed cameras, so its use may differ from the definition given above.

An iGO document explicitly identifies **FRC = Functional Road Class** in the section devoted to route calculation. Some discussions indicate that `min_frc` plays a role in determining whether the road speed is used, depending on its class: the value of `min_frc` would be related to the value assigned to `use_road_speedlimit`.

FRC 0 → motorway / major road
FRC 1 → very important road
FRC 2 → important road
FRC 3 → main road
FRC 4 → secondary road
FRC 5 → local road
FRC 6 → residential road
FRC 7 → road of very low importance

A specialized iGO discussion also indicates that `min_frc` works in conjunction with `use_road_speedlimit`, and that `min_frc=-1` is used when allowing the speed provided by the map to be used.

The most consistent interpretation is that `min_frc` is used to determine **from which functional road class iGO may use the speed limit provided by the map**, rather than simply determining whether the speed camera should be displayed.