Reference Information: Explanation of LOS rules

BattleTech Master Rules (BMR Revised page 26):

In all cases, 'Mech units are considered to be 1 Level high (at their firing/target position). Terrain along the LOS between units is intervening (blocking) if:

1. The terrain or terrain feature is higher than both units, or
2. The terrain or terrain feature is adjacent to the attacker and higher than the attacker, or
3. The terrain or terrain feature is adjacent to the target and higher than the target.

Maximum Tech Dead Zone Rule (Max Tech Revised page 21):

Players must check for dead zones if there is no intervening terrain higher than both the attacker and the target, but there is still some question as to whether LOS exists. Note which of the two units is at the higher elevation (2 in the diagram above) and which is the lower (1 in the diagram above). Then find the highest-level hex between the two units, designating it "Hex X." The elevation of Hex X (H in the diagram above) may or may not create a dead zone. To find out, follow the steps shown below.

1. Subtract the elevation level of the lower unit from that of Hex X. This number is "A." (In the diagram above, A = H - L1 - 1; remember, the lower 'Mech is 1 level above its terrain L1.)
2. Subtract the level of Hex X from that of the higher unit. This number is "B." (In the diagram above, B = L2 + 1 - H; remember, the higher 'Mech is 1 level above its terrain L2.)
3. Subtract B from A and multiply the result by 2. This number is "C." (Using the above values for A and B, this gives C = ((H - L1 - 1) - (L2 + 1 - H)) * 2 = 4*H - 2*L1 - 2*L2 - 4.)
4. Count the range to Hex X from both units. Subtract the range to the lower unit (D1 in the diagram above) from the range to the higher (D2 in the diagram above). This number will be negative if the higher unit is closer to Hex X than the lower unit. Add this number to C. (In the diagram above, (D2 - D1) is added to C, giving a total formula of Result = 4*H - 2*L1 - 2*L2 - 4 + D2 - D1.)

If the final result is greater than 0, the lower unit is in the dead zone and LOS is blocked. If the result is 0 or less (negative), then LOS exists between the two units. This equation can be put into another form:

    H = (L1 + L2) / 2 + (D1 - D2) / 4 + 1

This gives the maximum obstacle height, H, which does not block line of sight. Anything higher, does.

Note: Rules 2 and 3 from the BMR rules, concerning higher adjacent terrain, still apply, regardless of the LOS calculation method.

Important Note: IMHO the above calculation, while official Level 3, is wrong. Unless L1 and L2 are fairly close to each other, it can give answers that are absolutely incorrect. You may want to check out this Line of Sight Comparison and form your own opinion.

Maximum Tech Diagramming LOS Rule (MaxTech Revised page 22):

This alternate method uses a diagram, on page 22, but this diagram can also be put in terms of an equation. This equation, resulting from the geometry of the diagram in MaxTech, and using the variables in the diagram above, is:

1. Result = H - (L1 + (L2 - L1) * D1 / (D1 + D2) + 1)
2. Again, if the Result is greater than 0, LOS is blocked;. if the Result is 0 or less (negative), LOS is not blocked.
3. Rules 2 and 3 from the BMR rules, concerning higher adjacent terrain, still apply.

If the final result is greater than 0, the lower unit is in the dead zone and LOS is blocked. If the result is 0 or less (negative), then LOS exists between the two units.

As with the previous example, the above formula can be put into the form:

    H = (D1*L2 + D2*L1) / (D1 + D2) + 1

Again, this gives the maximum obstacle height, H, which does not block line of sight.

As noted above, it is my opinion that the official Level 3 formula from Maximum Tech is in error when D1 and D2 are different, greatly in error when they are greatly different, and I suggest using this Diagramming method and formula instead.

Please report any errors or questions concerning the code or results this page produces to Rick Raisley.

Note: You can save this page so it works on your computer without being connected to the Internet. To do this, using Internet Explorer, use the menu File > Save As, and select Save as Type: Web Page, complete. This saves the JavaScript code and graphics so it will work locally.

You may not, however, use images, HTML or JavaScript code from this or other pages. Please read our Terms of Use.

Page views since 03/07/2004