Grismar's EVE Wiki : SignatureRadius

Signature Radius

This article explains the concept of signature radius, its implications in EVE and how to make use of it.

The signature radius of a ship represents how large a ship seems for purpose of determining missile damage, tracking and the time needed to get a good lock on the ship. Note that it may also affect the time requires to scan with scan probes, come Kali.

For practical reasons, the signature radius of a ship is a single value, making the ship the same size in every direction, from every angle, for the above purposes. So it's just as hard to target or hit an Armageddon when you're facing it as when you're trying to hit its flanks.

Frigates generally have a signature radius in the range 30-50m, Destroyers about 75-90m, Cruisers 100-160m, Battlecruisers 240-300m and Battleships 320-480m. You can look up the exact data on specific ships in databases like ESSDB (oog).

Signature Radius and Tracking

Your guns require sufficient tracking to be able to hit a target that is moving across your line of vision. The basic tracking attribute assumes that you're aiming at a point and tells you how far your target is allowed to travel from that point in the next second.

For example, if your target is 25km away from you and your gun can track 0.02 rad/s, the target is allowed to move 500m/s and you should still be able to hit it. However, calculating tracking like that assumes the target has no size, but it does: signature radius. The larger the target, the easier it is to track, since you can miss the center by a larger margin and still hit.

Effectively, if the ship in the previous example had a 100m signature radius, it would have to travel at least 600m/s to avoid your shots (Note: these numbers still need verification). The larger it gets, the faster it needs to move to be able to dodge your bullets, blasts or beams.

Since the target painter increases signature radius, it effectively gives you a larger target to shoot and as a result, the target needs to move faster to avoid your shots. Activating a MWD also increases your signature radius substantially, so take that into account when using it.

Signature Radius and Missile Damage

When a missile strikes, it explodes, damaging only its target. However, missiles do have an explosion radius that is used to determine whether their blast is focused enough to actually deal all their damage to the target.

If the explosion radius is larger than the signature radius, only part of the damage is dealt. The damage from the blast is inversely proportional to the distance from the center of the blast. That may sound complicated, but it simply means that whatever part of the explosion radius is covered by the signature radius matches the part of the damage that's dealt.

For example, if your ship has a signature radius of 50m and is hit by a heavy missile with an explosion radius of 125m, the signature radius covers 40% of the explosion radius and only 40% of the maximum damage is dealt to your ship.

Signature Radius and Targeting

Your ship has a specific scan resolution. This indicates how fast it can target other ships. But the targeting speed is also dependant on the signature radius . The larger the ship, the easier it is to get a lock, so the better the targeting speed.

Note: the actual math on this eludes me at the time. Some experimentation needed to get the actual figures in here.

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Current EVE version: 2.13.25245 (Dragon)