Concering the LOS -
Progressive Block Point Addition
The original release of POA-2 used a purely additive method for determining LOS blocking. In this method, LOS points for terrain (as determined in the section above) were simply added to the LOS as it passed through each location. There was no consideration made for what the LOS may have already passed through, or the fact that the terrain may have overlapped to some degree.
Thanks to a suggestion by Peter von Kleinsmid, POA now uses progressive instead of additive accumulation of LOS block points. In the progressive method, terrain blocking points are adjusted based on what other terrain is in the current location or what terrain the LOS has already passed though. This method is more accurate, in that it models realistic random distribution and overlap between the discrete blocking features in each location (e.g., single trees, buildings, etc.).
To use a very simplified example, let’s assume that one tree causes 1 point worth of blocking, and 10 total points will block the LOS.
At first glance, it would seem that 10 trees should completely block the LOS. However, in reality this is rarely going to be the case because the trees won’t be exactly side-by-side. In fact, in the most extreme case the trees would be aligned perfectly behind one another (from the spotter’s perspective) and the LOS would only be blocked by 10%. In this case, the spotter would see only a single tree, while the other nine will be hidden behind it (and will have no effects on the LOS).
In the chart below, the vertical columns represent the five locations an LOS passes through (Evaluation Points), and the horizontal rows show whether a tree “position” is blocked or not. There are ten “positions” available - one for each of the 10 points needed to block the LOS. For simplicity, in this example single trees cannot be broken up - they can only occupy a single LOS blocking position.
A position (row) is considered blocked to the final LOS if it has at least one tree in it, otherwise it is open.
Using the additive method, the trees in each location would have been added together for a total of 10 blocking points and would have blocked the LOS (10% + 20% + 30% + 20% + 20% = 100%).
In reality, however, the LOS is only 70% blocked. Because the trees are randomly placed in each location, there is a discrete probability that some will overlap, based on the total number of trees in all locations. Overlap results in some tree positions having more than one tree, while others have none. In the above example, trees overlap in Position 2 (Loc 2 and Loc 5), Position 4 (Loc 1 and Loc 4), and Position 8 (Loc 3 and Loc 5). This overlap allows Positions 3, 7 and 10 to remain open.
The progressive model accounts for these statistical overlaps, and makes reduction to the base blocking point values as they are added. The reduction occurs at two levels: to determine the points of each location (for locations with multiple terrain types in them) and along the entire LOS (for each new location it enters).
Range Effects:
In addition to points added from passing through terrain, by default the LOS also accumulates blocking points based solely on the range between the spotter and the target. These points represent dust, distortion, diffraction, and other effects inherent in the atmosphere. The number of points added is based on the Maximum Sighting Range, which is set in the Game Conditions Form when creating a new scenario (Checklist step #4). By definition, at the Maximum Sighting Range the LOS generates 100 blocking points.
Blocking points are added proportionally based on the actual range as a percentage of the Maximum Sighting Range. For example, if the actual range is 40% of the Maximum Range, 40 points will be added to the LOS.
The default Maximum Sighting Range is 10,000 meters.
A secondary effect of long-range on LOS determinations is caused by the curvature of the Earth. The LOS calculations take this curvature into account, using the elevations of the spotter and target. The routines assume the Earth is a perfect sphere outside the area of the map. The LOS can never pass under the horizon (through the Earth).
Silhouetted Targets
The LOS routines also determine if a target is silhouetted, or outlined against a contrasting background - normally the sky. To do this, the routines “run out” the LOS a distance past the target to see if it intercepts the ground or terrain. If it doesn’t, the target is considered silhouetted. Otherwise it is not.
The range of the extra “run out” is a hyperbolic function based on the range between the target and spotter, but is always at least 500 meters.
