|2012-05-27||Bridges over troubled waters|
Bridges and rivers often lead to interesting battles. Also in Arma2. Recently, two new Arma2OA maps were released that featured bridges which the Arma2 AI is capable of crossing most of the time*.
To benefit from this, PlannedAssault now recognizes bridges and includes nearby bridges in its defensive plan.
With Jakerod's Zernovo map and =KCT=Blackmamba's Faysh Khabur map, we have been given two beautiful maps that happen to work for the Arma2 AI. Zernovo is a small map designed around a real-life German river section. That rivers is crossed by multiple bridges so they connect several small towns. The map features West-European farm lands with subtle height differences separated by tree lines. Roads are slightly elevated, enabling hull down positions.
Faysh Khabur represents the Iraq-Syria-Turkey border area in Iraq's Dahuk province. The area is partitioned by a wide yet shallow Tigris river, with just two bridges allowing traffic to cross. The terrain is barren, offering little concealment and long engagement ranges.
What these two maps have in common is that their bridges present great tactical opportunities, especially for the defender. Unless the attacker is capable of amphibious assaults, the bridges funnel him into predictable approaches, as you can see from the screen shots in this update.
To make the defender benefit from bridges, I've extended PlannedAssault with the ability to (1) identify bridges and causeways in Arma/VBS2 terrain, (2) include nearby bridges in the selection of defensive sectors, (3) explicit generation of 'defend bridge' orders for AI and player teams, and (4) pre-registered artillery targets at the far side of bridges included in the defense.
To identify bridges I've had to perform some new terrain analysis. The Arma/VBS2 terrain files do not indicate which objects are bridges, the default location types don't include bridges, and the in-game scripting API does not support queries for bridge objects.
It isn't too hard to identify bridges: typically they are roads with water on both sides. It proved harder to get rid of the false positives: roads with water on both sides that aren't bridges, such as piers and harbor installations and land ends.
All maps featuring bridges (Zernovo, Faysh Khabur, SaraLite) and causeways (Quesh-Kibrul) have been updated with a new terrain database identifying bridges for mission planning.
To identify the most important defensive sectors for an objective, I generate set of sectors around the objective and test which of those sectors are likely to be used by an enemy trying to attack, with infantry or with vehicles. I've updated this approach by adding nearby bridge sectors and giving these bridge sectors a bonus for predicted enemy attacks across them. This bonus reflects bridges being effective bottlenecks that are more easily defended than a wide sector.
One of the pictures in this update shows the difference between defensive sectors as selected previously versus defensive sectors selected while taking into account bridges.
When bridge sectors are included in the defense, the teams are given explicit orders to defend the bridge, per the usual tasks generated with each and every PlannedAssault mission. These are shown in the briefing, and in the HUD as 'new task assigned'.
The final bridge related improvement is a continuation of the earlier defensive behavior. At the far end of each of the defensive sectors a pre-planned fire support target ('TRP') is defined, into which fire support is requested by the AI when hostile ground forces are observed there. This means that the far side of the bridge is 'prepared' for a quick artillery mission. When the attacker moves into this area and, typically, bunches up to get across the bridge, this pre-planned fire support may take a lot of punch out of his attack.
Something not related to bridges: I've been testing my generated missions for Zernovo and Faysh Khabur using two new Russian Federation add-ons. First is Colonel Stagler's Spetsnaz GRU in various kinds of uniforms and camouflage, with and without backpacks. Second is Cmp's Russian modern moterized infantry, in flora, digital woodland and desert camo. Both have been added to the add-on database for Arma2:CO.
Enjoy the bridges!
*: Although many more (Arma1, VBS2 and Arma2) maps feature bridges, on very few of those maps the AI is able to reliably cross these bridges.