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Turret Mechanics (Part 2) – Transversal vs Angular Velocity

(You might want to read Part One first.)

Imagine that you’re sitting still, at zero m/s.  You have three targets nearby:

  • A Rifter (red) is orbiting you at 500m.  They’ve got their AB on, and are keeping up a steady 1200m/s speed in that tight orbit.
  • An artillery Wolf (blue) is orbiting you at 20km with MWD.  They’re moving at 3600m/s.
  • A Jaguar (gray) is burning directly at you at 2500m/s with MWD on.

14dec2015_transversal

Let’s assume, for now, that you had artillery with infinite range.  The damage you do is determined entirely by tracking.  Which one do you shoot?

When you customize the set of columns that Eve puts in your overview panel, there’s four options for you to choose from:

  • Basic velocity — Shows how fast they’re moving in their direction, in meters per second.  Ignores anything you do.
  • Transversal velocity — Take your direction, and project the target’s movement in that same direction.  Take that part of their movement that’s parallel to your direction, subtract it from your speed, and display the difference.  Measured in meters/second.
  • Radial velocity — The rate at which they’re approaching or retreating from your ship.  Draw a direct line from your ship to their ship, and measure how fast it changes length; ignore the line’s direction.  Measured in meters/second.
  • Angular velocity — the rate at which they change angle to you.  Draw a direct line from your ship to their ship, and measure how fast it sweeps around your ship; ignore the line’s length.  Measured in radians/second.

Notice that angular velocity is different from the other three in the units it uses — in fact, it’s the exact same units that are used to measure the tracking speed of guns!

Returning to our example:

  • Because we’re not moving, all of the ships have the same transversal velocity as their normal velocity, meaning that the Rifter has the slowest transversal, and the Wolf has the highest.
  • If you have radial velocity on overview, the Rifter and Wolf have zero radial velocity (because they’re orbiting you at a fixed distance), while the Jaguar is approaching you at 2500m/s.
  • If you have angular velocity on overview, the directly approaching Jaguar has zero angle, and is easiest to hit.  The Wolf may be moving quickly, but it’s doing so from a great distance, so your turrets only need to move a pokey 0.18 radians/second to track it.  The Rifter, meanwhile, is moving at a zippy 2.4 radians/second.

Transversal is the most familiar to Eve veterans, because it was the only thing available in the early days of Eve.  In theory, it provides easy feedback to how quickly something’s moving away from you — if it’s low, then you’re moving parallel to a target, and should shoot.  However, transversal often lies to you, especially when you’re moving slowly or looking at distant targets; it only becomes consistently useful when you’re skirmishing with another moving target at a moderate distance.

If you’re trying to figure out what you can hit on the battlefield, angular velocity gives you a much more accurate view of the field, and it directly corresponds to the tracking of your guns.  If I know my artillery has a tracking value of 0.013 (radians/sec), then I know that I’ll be able to track and hit anyone on my overview who has an angular velocity less than 0.013, assuming they’re in my optimal range. [1]

In practice, I actually tweak my overview based on what I’m flying.  For artillery and other slow-cycling weapons, or for very slow ships, I use angular velocity.  When I’m flying Taranises and other ships with fast tracking and high speed, I use radial velocity, since that tells me how quickly something is approaching me.  I almost never have transversal on my overview anymore; the only time transversal is notably useful is if I’m trying to fly parallel to someone at a distance, and that rarely happens in modern Eve where kiting tactics are common and speed are essential.

How is this relevant to turret damage?  Remember from Part One: turret damage starts by calculating a chance-to-hit for your guns, and then making a dice roll to determine if you hit (and what the damage is).  Angular velocity and tracking go hand-in-hand in calculating that chance-to-hit.  We’ll discuss how it’s used in Part Three.


1. CCP, if you’re reading this: It’d be significantly either to use both the tracking speed in Show-Info panes, and the Angular Velocity overview column, if you multiplied both numbers by 1000.  Call it milliradians/sec.

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Turret Mechanics (Part 1) – Roll For Initiative(dot)

The easiest way that I’ve found to explain turret mechanics is a throwback that should make immediate sense to tabletop RPG players:

Every time you activate a turret, the Eve engine calculates a chance-to-hit percentage. You then roll a 100-sided die (D100), and use the following rules:

  • If you roll a 1, you get a crit (wrecking blow) — a guaranteed hit for triple damage. [1]
  • If you roll any other number less than or equal to your chance-to-hit, you hit.
  • If you roll a number greater than your chance-to-hit, you miss.

When you hit on any number other than a 1, you take your roll, add 50, and treat the sum as a percentage of your turret’s base damage.  So, assuming that you’re shooting a stationary target at optimal range (100% chance to hit), each roll of the dice can produce a hit ranging from 50% of base damage (a glancing blow) to 150% of base damage (a penetrating/smashing shot).

As your chance-to-hit starts dropping, not only do you start having rolls that miss, but your highest quality shots are the first ones to get converted to misses.  For example, lets say that you have a 75% chance to hit a target; that means you hit on a roll of 1-75, and miss on a roll of 75-00.  That means that you will never hit for more than 125% of your base damage; you cannot get penetrating shots.  As it drops off, not only do you have more chances to do no damage on a shot, but your shots that hit will be of increasingly lower quality.

This is the main way that damage drops off with range, and it’s particularly important for alpha-strike doctrines; fighting in falloff doesn’t only reduce your fleet-wide average damage per cycle due to misses, but it dramatically depresses individual volley damage as well.  Likewise for shooting targets with tiny signature radii.

The other crucial part of turret mechanics is how we actually compute the chance-to-hit percentage.  That’s complex enough to be its own topic, and it’ll be in the next post.


1. Wrecking shots aren’t actually a guaranteed hit — you can only get a wrecking shot if you have a non-zero chance to hit, even if it’s very small. Imagine that you’re in an artillery Tornado with Quake loaded, and an AB Taranis is orbiting you at 500m; you have a near-zero chance to hit it, due to tracking, but it’s still a tiny fraction above zero.  Thus, wrecking shots are possible.  Now, imagine that the same Taranis is 225km away; you have a strictly zero chance to hit with EMP, even if both you and it are completely stationary.  You will never hit it, even if you roll a one.