Mobile obstacles are objects that penetrate the obstacle collection surfaces without having a fixed location. The total perimeter of the potential penetration is captured, irrespective of the obstacle actual location.
The geometry should be a line or a polygon, depending on the movement area footprint penetrating the obstacle collection surface. The threshold definition as specified in EUROCAE ED-98C App G can be used to determine the exact geometry of the footprint, i.e. a line or polygon.
If the mobile character of an obstacle is not relevant for aviation, it should be considered as a 'static' obstacle with a horizontal extent. For example, in the case of a railroad with an overhead power line, the power line is the relevant obstacle (not mobile). The trains moving on the railroad are irrelevant in this case.
Obstacles at fixed positions with variable geometry are not considered mobile obstacles. Please refer to Obstacles with variable geometry for the appropriate coding guidelines.
Typical cases for mobile obstacle are obstacles moving along a line or within an area, e.g. ships, cars or rail mounted cranes.
The VerticalStructurePart.mobile property may be used to indicate that the VerticalStructurePart is expected to move around its nominal location. If the VerticalStructurePart.mobile property is set to "YES", then the obstacle is moving along a curve or within the boundaries of a polygon. Therefore a point obstacle can never be mobile.
It is assumed that the VerticalStructure.width property for a curve, respectively the polygon covers the entire horizontal extent of the moving part, i.e. no part of the obstacle is outside these limits. If, for example, a crane moves along a line, the width of the line should be selected to cover all possible positions of the crane's jib.
Mobile obstacles may also have a schedule. For example, trains on a railroad can be present only at certain times. In this case, the VerticalStructurePart (line or polygon) concerned may have associated Timesheet(s).
Coding as polygon or line depending on area
Roads, railroads, powerlines and other line shape obstacles can be modeled either as lines with a width or as polygons. EUROCAE ED-98C App G.3 gives some guidance, when such obstacles shall be coded as a polygon rather than a line, namely if the width of the footprint penetrating the collection surface:
- for Area 1 if larger than 100 meters, or 32 meters for helicopter requirements
- for Area 2 if larger than 10 meters
- for Area 3 if larger than 1 meter
- for Area 4 if larger than 5 meters.
This means that small and narrow roads in Area 1 can be simply modeled as a line, whereas the same object in area 2 should be modeled as a polygon.
Regardless of the shape, it is essential to code the highest elevation of the obstacle in the elevation property of the elevatedCurve or elevatedSurface element of the VerticalStructurePart.
Rail mounted cranes
A gantry crane (picture below left) or a container crane in a harbour can move in a limited area defined by the rails. A rail mounted gantry crane is captured considering the height and the maximum area of movement, which defines the footprint of the obstacle (picture below right). Then, the relevant footprint of the object is considered taking into account the penetration of the collection surface.
Such a crane should be coded as a VerticalStructurePart.horizontalProjection of type ElevatedSurface.
Moving obstacles (cars, trucks) on a road
Such mobile obstacles are captured as a polygon considering the maximum height of the trucks using the roads and the lateral boundary of the part of the roads relevant for the operation.
Small roads may alternatively be coded as line obstacles with a width (see above).
Ship channels are areas, where vessels may be present in any part of the area. In the example below there are three ship channels with different maximum vessel heights:
- up to 15 meters in the red area close to the runway
- up to 30 meters in the yellow area
- up to 49 meters in the blue area
Vessels exceeding these limits might still be possible, but shall be announced by NOTAM or ATIS.
Since these areas are quite large and clearly located in Area 2, they shall be coded as polygons with the maximum ship height as elevation.
In this example the waters are sea level, therefore the elevation equals the height. In cases of water bodies at higher elevations (e.g. rivers, or lakes) the elevation should be the elevation of the water plus the hip height.
Mobile cable cranes
Cable cranes are mobile constructions used for logging woods in hilly forests. They are moved within a known perimeter every few days. The obstacle is captured as a polygon with an elevation of the highest possible point of the crane.