Playing the vanilla game with the existing trade resources is fine as far as gaming goes, but to achieve "total realism" several of the trade resources need to be modded, both in terms of location and the resources themselves. Location is easy to change -- simply alter the x,y coordinates in the descr_strat.txt file (or make new entries in imitation of the existing ones).
Changing the resources themselves is more of a challenge. The master file here is descr_sm_resources.txt, which is found in the "text" subfolder of the "data" folder. This file will allow you to do three things:
1) Change the base value of each resource
2) Change the graphic for that resource that appears on the campaign map
3) Change the icon for that resource that appears in the trade summary chart for each settlement
#1 is quite easy just by looking at the text file. The higher the number assigned, the higher the base value (Gold has a high value, around 22, while more common resources are around 5). No big challenge here.
For #2 and #3, I decided to change sulfur to salt. (Sulfur later became an important industry in Sicily, but only really took off in the 17th century when mass production of firearms became common. Salt, on the other hand, was a major trade item in medieval times and a significant basis for the prosperity of Venice, Salzburg, Mallorca, Provence, Lubeck, and several other places).
The practical advantage of this transition is that the game graphics for sulfur are both piles of yellow powder, and this can be fairly easily changed into piles of white powder. To do this, went into the original (unmodded) "data" folder to retrieve three files:
a) under data/ui/resources, I grabbed the resource_sulfur.tga file. This is the icon that appears in the trade window. I opened it in Photoshop and turned it into a greyscale ("remove color"). Then I saved this file as resource_salt.tga in my mymod folder under mymod/data/ui/resources (had to create new folders to do this).
b) under data/strat_models, I grabbed the resource_sulfur.cas file. I saved this under mymod/data/strat_models as resource_salt.cas.
c) under data/strat_models/textures, I grabbed the corresponding texture dds file for sulfur. I opened this in Photoshop (using the dds plugin), and again I removed color. I also had to brighten the image to make it closer to white. Then I saved the file UNDER ITS ORIGINAL NAME (sulfur) under mymod/data/strat_models/textures. It must be saved under its original name, unless you go in and change the .cas file, because the .cas file is still going to look for something called "sulfur" to grab the texture it needs.
Then you go back into descr_sm_resources.txt and change the links under that resource to call up the modded files. You must add mymod/ (or whatever name you are using for your mymod folder) to the beginning of the addresses, so it knows to look for the modded files in the mod folder. Otherwise it will look in the original data folder and call up the unmodded files or (if you've changed the file names, like I did) nothing. So, for example, the icon address would be mymod/data/ui/resources/resource_salt.tga. Make sure you keep the tga and cas files clear in your mind. The tga is the trade window icon, the cas refers to the campaign map graphic. In fact, it is best to mod these links one at a time so if there is any problem you can isolate the cause.
When you load the game now, if everything has been put in its proper folder and the links changed correctly, you should see a pile of white powder on both the campaign map and the trade window. However, you will see that it is still named "sulfur". To change this, you need to mod two strings.bin files, and here's how:
Download pmcorp's strings.bin editor, which can be found at:
http://www.twcenter.net/forums/downl...do=file&id=993
This is a lifesaver. Now backup two files in your original data folder, strat.txt.strings.bin and tooltips.txt.strings.bin. Open strat.txt.strings.bin using pmcorp's editor. Find the line where it says "Sulfur," select it, and edit it to say "Salt", then save under mymod/data/text. Please not that although you may have an unconverted strat.txt file, changing this will not be reflected in the game, because this file does not self-generate a strings.bin file in the mymod folder, and when the game doesn't find a strings.bin in the mymod folder, it goes looking in the unpacked files. You must copy a modded string.bin file directly into your mymod folder for the edit to take hold.
Go through the same process with the tooltips.txt.string.bin file. Note that we were never given an unconverted text file for this, nor does alpaca's converter appear to work. You must mod this directly using pmcorp's tool. Change "Sulfur - a valuable trade resource" so it says "Salt - a valuable ..." instead. Now save it to mymod/data/text.
You should be done. When you load the game, you should see white piles that say "salt", both on the campaign map and the trade window.
You can also edit trade resources by introducing .cas, texture, and .tga files from RTW. For instance, I replace coal (which was not really traded long distances in the middle ages) with glass (which was) by adding the graphic files for glass from RTW. You may need to unpack your pack files in RTW to access all of the required files.
Presumably someone who is much better than I am at 3-D modeling and texturing could create entirley new .cas models for new resources. But the RTW files offer a pretty good starting pool of easily modable graphics.
Note that M2TW has three resources -- elephants, dogs, and camels -- which appear not to have any game function. Presumably these too can be modded into new resources. I am not sure whether the game allows you to add completely new resource on top of these, however. At the very least, this would require access to an uncoverted tooltips.txt file, in order to create the links between the tooltip entry and the underlying resource code. I won't bother to try for now.