Hi

I have played a game (Sid Meier's Railroads) and a few days ago I installed it again to relieve some fun memories.

While I was playing I noticed that when my railroad crossed rivers or a ravines then the game would create a bridge and it is this part which have me puzzle:

The bridges were never too short no matter how wide the gap were the bridges just got longer to neatly (I dare say) fit the gap.

If anyone wants to bother having a look then there is a tons of screenshots on google.

Now to my question:

How was this made ?

My own guess is (and I'm not a programmer, which is why I'm asking you !) that the developers made the bridges in three segments:

1. a start segment

2. a middle segment which is expandable

3. an end segment

Here is another thing I don't understand:

How the the program knows:

1. how many middle segments to add

2.how pick the most suitable type of bridge for a particular gap

http://www.gbase.de/uploads/ci/shots/Sid-Meiers-Railroads!_b_55738.jpg

http://storeimages.impulsedriven.com/product_gfx/04xx.jpg

http://tjstatic.com/multimedia/2011/07/sid-meiers-railroads-pantalla-1.jpg

I hope someone would like to enlighten me.

Disclaimer: I don't know WTF I'm talking about !

Hi

First of all: Thank you all for taking your time to reply

@Poigahn

It is hard to give a comment on your reply as I'm not sure which of the images you're refering to, but my best guestimate is that you're refering to the yellow brick-like structure.

@Aardvajk

You also seem to have set your sight on the yellow brick-like structure.

@BCullis

Thank you for the link - I'll admit I get a little dissapointed when I discovered it was about Flash, so I did a search, but in vain as I couldn't find any site which could privide me with an explanation I was able to comprehend (I don't blame you, but instead my mom and dad !)

Anyway, since you all seem to somewhat agree on how the yellow brick-like structure was made (and I have to agree too), I would then like to point your attention the the truss bridge found in two of the images.

This is not made with the same technique as you have described in the above.

My guess is that this bridge is made from a set of predefined rules:

(psudo code)

While laying tracks

If encounter a depression (ravine or river)

Then start with a steel truss bridge with three bridge segments (ie. a start, middle, and end segment) to close the gap - did it work ?

if yes then continue to lay track

else

Then start with a steel truss bridge with three bridge segments (ie. a start, 2 x middle, and end segment) to close the gap - did it work ?

if yes then continue to lay track

else

Then start with a steel truss bridge with three bridge segments (ie. a start, 3 x middle, and end segment) to close the gap - did it work ?

if yes then continue to lay track

else

Then start with a steel truss bridge with three bridge segments (ie. a start, 4 x middle, and end segment) to close the gap - did it work ?

if yes then continue to lay track

else

Then start with a steel truss bridge with three bridge segments (ie. a start, 5 x middle, and end segment) to close the gap - did it work ?

if yes then continue to lay track

else

add an "elastic" bridge segment and when there is enough left add another steel truss

(psudo code END)

There are most likely a few more parameters, but the one I just described in my psudo code is the most obvious, based on what I can see in the images.

Does anyone of you have anything to add (I could be the case that I have gotten it all wrong, which certainly wouldn't be the first time !)

(I don't blame you, but instead my mom and dad !)

Which is what your pseudocode does, kind of, only it wouldn't be quite so ...voluminous. Just write an algorithm that looks at the distance you need to cover, determine how many repeating elements it will take to fill that gap, and place them.

Disclaimer: I don't know WTF I'm talking about !

Hi

Thank you for your reply.

As I read and understand your algorithm it would continue to add middle segments until it had nearly closed the gap and just slap on an "end" segment - if this is true then some of the bridges would look rather strange and really long - some of them might even end up defying every book that been written about load-bearing capacity in bridge spans due to their huge distance between their pylons !