"How do you handle terrain blind spots" Topic

Specifically behind hills. I'm looking for a quick and simple rule to use in my ECW rules to calculate how far from the crest of a lower hill (from the observers position) the dead ground extends. I'm not looking for detailed trigonometry here just a rough approximation that reflects the relationship between the height of the observer, the height of the intervening (lower) hill, the distances between the observer and the target, and the target and the crest of the lower hill. E.g. observer is at 200 feet target is at sea level and the intervening hill is 100 feet high the two hill crest lines are lets say 100 feet apart. how close to the crest line of the lower hill would the blind spot extend to?

But I really want a rule that can be applied to different positions and height differences on the game table. To make things fun it seems most game designers fudge this so I guess its not easy to to create a simplistic rule.

Answers on a postcode to that damn Pythagoras bloke, Greece. or better yet post below!

How about:
Distance between observer and intervening hill/(height of observer – height of intervening hill) x height of intervening hill.
Using your figures
100/(200 – 100) x 100 = 100 foot deep blind area

If the observer is on a 300 foot high hill:
100/(300 – 100)/x 100 = = 50 foot deep blind area.

And if the observer is the same height as the intervening hill:
100/0 x 100 and the blind area is infinitely deep.

This assumed that the observer is prone (otherwise add his/her height to eye level to the height of the hill he/she is standing on) and disregards the curvature of the earth.

Or you could just say that hills obscure line of sight.

John that sort of mirrors what i had in mind. If anyone else wants to chip in or has an example of how other rule sets cover this I'm still open to ideas.

Any visibility rules inevitably boil down to trying to determine…

…how much of what I'm standing here looking at can I see…?

There are only 2 really workable solutions, and both are a pain.

1. Double Blind. Have 2 identical tables set up with only those things each respective command can see on their table. As they move and expand the scope of their view, items are placed on the first table, matching to the other.
2. Table Screens. Relatively tall walls dividing the table which are moved/removed as appropriate.

How about just using a periscope on the table? I made one using a long narrow box, and a cheap cosmetic compact mirror. I put it on the table at the sighting figure, then I look through it to see if they can see the target. Easy-peasy. Otherwise, use a laser pointer to see if there is clear LOS, placing it at the shooter's position, pointing at the target. Cheers!

I have a military map reading manual which tells you how to calculate this sort of thing. Trigonometry is involved.

A much simpler solution for Wargames purposes is just to fudge it. A higher level hill can see over a lower level one, but there is an area of dead ground some notional distance deep. A couple of hundred yards.

Another approach is to borrow from Panzerblitz. If the lower obstruction is over half the distance to the target, you can't see it. If it half distance or less, you can.

I was wondering how relevant this is to the ECW though? Observation from hills matters a lot more in the eras of high velocity AT weapons, indirect artillery fire and ATGMs.

Our Rules use the following (unfortunately picture don't work on here). Now to be fair this is at least partly artifice but as we have found before, something even very approximate is better than nothing.

Our hill's are approximated (typicaly) as a slope with a flat top. This is not perfect but it does seem better than any other simplification.

Our hills have a crest line (interface between slope and crest). The crest linesheight needs to be defined.

So an element looking out from the crest then has dead ground measured in the line of sight from the base of the hill.

Typically war games hills are only very low (6 figure heights is a very rare occurrence in my experience and my own practical experience is slopes above 1 in 2 and practically, 1 in 4 is much better, otherwise figures won't stand on them. On this basis there are already some big limitations to what can be represented anyway.

Actually on the slope we impose only LOS limitations. This is not as bad as it seems as even a 2 figure high hill has a slope length of about 4 1/2 figures so not that much of the table so not a massive approximation.

In the section below a Contour is about 16 to 20mm tall so the dead ground is 4 contour heights per contour FROM THE BASE OF THE HILL. We measure from the base of the hill on the line of sight so at least we pay lip service to the fact dead ground is greater when looking obliquely.

Extract from MANEOUVRE GROUP

10.2.7 Dead ground

Hills, Ridges and folds have dead ground (areas that are not visible). Hill dead ground zones are measured from the base of the hill on the line of sight of to the target at a rate of 80 m per level. (See diagram below).
In addition elements on the crest line may see up or down parallel to the crest for 20m .

PS you can use the system to work out blind spots behind woods etc. Again a horrid approximation but we assume 3 contour height for trees. Th8is is close to war games trees but miles off a full grown tree. However full height trees look daft on a war games table the figure to ground scale errors becomes way to obvious.

Hill view from above showing dead ground measurement from edge of hill

I am happy to answer questions on this, as this is not the complete description but it seems long enough for one post.

More thanks for the additional input. To answer Martin's question about the importance of LoS in the ECW. There were situations where it had an impact. For example at Naseby the advancing Royalist Foot were in dead ground for most of their advance towards the NMA position. This meant that there was a very limited musketry exchange before they came to close assault.

I'm happy to use a fudge because I can't assume that players will have a laser pointer or periscope or want to buy one. Plus the result would be open to debate and you know how argumentative some of us wargamers can be!

Us ha has reminded me about flat Hill tops, a very useful Wargames mechanism as they provide a simple and visually obvious way of modeling reverse slopes. Are you on the forward crest or not?

I first came across this approach playing Squad Leader back in 1980 when my opponent set all his squads up a hex back from the crest of Hill 621, and I was utterly stumped as to how I was supposed to shift them without just charging into their point blank (doubled at one hex range) fire.

Martin,
I'd suggest a Prep Fire mortar barrage on them.

Wolfhag

I find "the obstruction can be seen over if it is closer to the firer than to the target" to be a close-enough rule of thumb. At least until your figure:ground scale gets close enough to 1:1 that you can use true line of sight.

It mostly comes down to what height is your hill / contour.
Low differences in flattish terrain can have big impact. Look at Ruweisat or similar things in ww2. Once I was walking Loigny batylefield, though it looks flat, there are numerous folds and curves, you can hide a brigade from Krupps in each.
Define the stuff for each battle, the simple ways ( 1 more level half distance blind etc.) as said above like in boardganes work fine.

I have heard lots about define on the day. That is I guess is perfectly acceptable if you play 3 or 4 times a year. If you play 40 times year like me, all those separate definitions blur and you get confused. Better to have a standard rules and only change for very rare occasions (once or twice a year).

If the enemy unit is within 1" of the hill then it is in its shadow.

If you have multiple levels of hill use 1" for the greatest possible difference, then add additional distance equal to the size of a standard unit for each decrement.

E.g. if your units are 4" wide and you have 4 hill heights then the greatest height difference you can have is 3 levels. This uses the within 1" rule. 2-level difference is 5". 1-level is 9".

Define: because of the usual limitations of games. You hardly manage hills contours or heights of say 2-4 levels at most. You can easily have terrain that counts of very different heits.
For my example, the Loire campaign 1870-71 is in a deceptively flat place, but there 34 m differences will habe a big impact on your battle.
Same period you may fight in the East, Spicheren, Froeschwiller where heights differences are way bigger, and the impact for your very question shoukd be different giving the inhetent limits of your table.
You can have 2-3 standarts. Plains, rolling terrain, mountaineous.

Jcfrog, I play at approximately 1:1 scale so to aid visualisation hills are at least in height terms, roughly what they are at model scale but about 7 times bigger in the X, y direction as the ground scale is about 7 times the figure scale. Now you can obviously play on a ground scale much greater model to ground scale difference than thst than that. However to me personally that to me becomes a map game and to me best played as a board game, but that is personal preference.

If playing on a map then inevitably the issue is more complex and you would need far more complex rules. My own experience is that something plausible, just, can be achieved modelling crest lines even if far to low a height, providing you are not in mountainous terrain. We decided attempting mountainous terrain at large scale was beyond what we considered practical given what we requied of our model terrain.

The rules I need this for are 1:1 ground distance and height. So actual LoS works. I have settled on the tight string method. Thanks for an interesting discussion plus some great ideas.