Ranging and fire control problem

[Charos]

I would like to invite others to test and see if they conclude as I have that the Attack periscope as well as the TBT field of view and graticule markers are not correct.

This also affects the TDC as its using the wrong parameters.


The following screenshots are of a stationary Iowa class Battleship broadside With a
S-Class submarine also stationary.

The attack periscope should have a FOV of 8 Deg divided by 32 graticule markers of 0.25 Deg each. (In high magnification 6X setting)

The Iowa is 270M long and has a mast height of 46M.

Now for an 8 Deg FOV to see the Iowa fill the entire screen would require a range of
135M/Tan 4 Deg = 1930M .


Now for a mast height of 46M and a Range of 1406M (This range is from game stadiometer) we see the mast fills 5.5 Graticule markers in the Attack periscope (see attached screen shot)









Each marker SHOULD be 0.25 Deg (IE 8 Deg/32 = 0.25) as per game manual.

Mast /Range = Tan (Theta) in this case Theta = 0.25*5.5 = 1.375 Deg.

Solving for Range = 1916M (Which is very close to the previous 1930M and within error tolerance reading from stadiometer)


Note the Iowa in SH4 fills the 6X attack scope at approx 1680M (see attached screen shot)

Also note that the TDC via the stadiometer provides us a range of 1406M (see attached screen shot)

Something is clearly wrong…Yes?


Now lets dig a little deeper into the problem………………


To cut a long story short the Graticule markers are not 0.25 Deg but approx 0.29 Deg.

135M = Half Iowa Length.
4.64 Deg = Half Attack Periscope FOV.

IE: 135M/4.64 Deg = Range
Range = 1663M (Which is correct in our example).


So that attack periscope markers on 6X and its associated FOV work off 0.29 Deg per graticule marker for its 9.3 Deg of view.

But what happened to our TDC its showing 1406M ????

Well its working off approx 0.34 Deg per marker for Range finding (IE: off the vertical graticule scale) which makes things even more strange.

Hope this all makes sense.

[joea]

Bug!!! ..can it be fixed or modded? My head hurts. Nice work though.

[Joe S]

My math skills are limited to basic multiplication , division, addittion and subtraction. Based on your research, what is the actual magnification of the scope in high and low power? Once we know the magnification, how do we use the recticle to get the range of a target? thanks! Joe S

[Charos]

Originally Posted by Joe S

My math skills are limited to basic multiplication , division, addittion and subtraction. Based on your research, what is the actual magnification of the scope in high and low power? Once we know the magnification, how do we use the recticle to get the range of a target? thanks! Joe S

Joe going by the real life values of the following:


Type II
Magnification high power 6.0X
Magnification low power 1.5X
Maximum elevation of line of
sight (above horizontal) 74.5 degrees
Maximum depression of
line of sight (below horizontal) 10 degrees
True field high power 8 degrees
True field low power 32 degrees
Ranging Device Stadimeter
Telemeter
Scale

Outer diameter reduced section 1.414 in
Optical length 40 ft


Type IV
Magnification high power 6.0X
Magnification low power 1.5X
Maximum elevation of line of
sight (above horizontal) 45 degrees
Maximum depression of
line of sight (below horizontal) 10 degrees
True field high power 8 degrees
True field low power 32 degrees
Ranging Device Radar
Telemeter
Scale

Outer diameter reduced section 3.75 in
Optical length 36 ft


You can see that both the Observation and Attack scopes have 6X and 1.5X
magnification at 8 Deg and 32 Deg Field of view respectively.

You can see that the pattern:

8 Deg = 6X
32 Deg = 1.5X

Therefore 16 Deg = 3X
and 48 Deg = 1.0X

So the attack periscope on high magnification in SH4 provides approx 9.28 Deg FOV
or approx 5.17X magnification.


This whole thing to my mind is the most URGENT Bug in SH4 as it takes the whole TDC measurements out from what they should be.

[Charos]

Im bumping this.

To put this problem in simple terms it means the Games TDC is providing a 17% Ranging error on all firing solutions.

I hope the magnitude of this problem has not been lost in the we need a working chronometer white noise.

In my example above the TDC has clearly provided a range solution of 1,406M while the sub the TDC is sitting in is STATIONARY and approx 1,680M from the target.

[jmr]

Great investigative work here. Hopefully more experienced skippers than myself can give their input on your results. All I can add is that I've been practicing with Kim Ronof's Mark 3B range calculator and my results don't jibe with the auto TDC.

[SteamWake]

Very well done.

Lets hope someone can get to the root of this.

[joea]

This must go on the bug list.

[Charos]

Although im confident there is a major problem here I still require at least another person to verify this so as we can be 100% shore im not barking up the wrong tree.

Anybody?


Just fire up the mission editor and place one stationary sub and any stationary ship and check stadiometer distance with ingame map distance as a starter.

For confirmation they should be out by 17% from each other.

[akdavis]

Hmm...I've certainly noticed that the stadimeter does not measure range consistently, but it seems to vary from ship to ship.

[Charos]

Originally Posted by akdavis

Hmm...I've certainly noticed that the stadimeter does not measure range consistently, but it seems to vary from ship to ship.

I have tested this myself on the Iowa BB and the Kongo BB as well as the small tanker (which has the 20M mast) or 19.7M depending on which reference.

In any case my results so far in my testing have shown consistancy.

There may be some slight variance in boyancy of the vessels (if this is modeled) but the error could not be that high. and the horizontal graticule scale is the same as the vertical scale IE: 0.25 Deg - and as I have shown that is also off by the same amount as the vertical scale.

[Charos]

Originally Posted by akdavis

Hmm...I've certainly noticed that the stadimeter does not measure range consistently, but it seems to vary from ship to ship.

To be more specific the reason you most likely see a variance in distance error between TDC calculated range and actual range on game map is because the difference is a percentile error.

The error is approx 17% - the further you are from the target and or the smaller the mast height is the greater the difference in distance will be - but the difference is still 17%.

[SteamWake]

The comment that "it seems to vary from ship to ship" made a light bulb go off

Its not the Scope thats in error its the models ?

[akdavis]

Originally Posted by Charos

I have tested this myself on the Iowa BB and the Kongo BB as well as the small tanker (which has the 20M mast) or 19.7M depending on which reference.

In any case my results so far in my testing have shown consistancy.

There may be some slight variance in boyancy of the vessels (if this is modeled) but the error could not be that high. and the horizontal graticule scale is the same as the vertical scale IE: 0.25 Deg - and as I have shown that is also off by the same amount as the vertical scale.

A simple test can be conducted in the training missions. In the artillery mission, you will get a correct range (as compared with map contact updates on) by measuring from the tip of the merchant's masts, as the documentation instructs you too. In the torpedo mission, you must lower the stadimeter image down further on the Mogami to get an accurate range. More like the first crosstrees rather than the top of the masts.

[Sailor Steve]

Picky, picky, picky!


But only because I probably never would have noticed, and certainly couldn't have figured it out mathematically. Hope you get it solved.