I am attempting to modify a model of a house that was first made by another user of a transport simulation game, Simutrans. My modified .blend file of the model is here (distributed under the Artistic Licence). Note that it will eventually be rendered as 128 x 128 pixel images for the game, so it doesn't need very fine details.
I would like to change the replace the original textures of snow on the house with JPGs of a slate roof and bricks on the walls. These JPGs were supplied by the original modeller and are available (under the Artistic Licence??) from a Simutrans repository.
I have changed the roof texture to the slate JPG, but the image appears as a series of diagonal tiles. The brick texture for the walls has the same problem. These diagonals appear completely unrelated to the meshes.
Why are the textures diagonally tiled? How can I have one image on each roof and wall? If the (2D) JPG was mapped onto the relevant (2D) faces, that would probably be sufficient. Ideally, I would like to have the slate image repeat three times, once for each of the terraced houses.
A Failed Attempt to Solve This
I guessed that the answer lay in the Mapping tab. By changing the 'Coordinates' setting from 'UV' to 'Global' and the 'Projection' setting to 'Flat' I was able to get one slate image on each roof - success! However, the tiles are now displayed at 90° from the desired orientation on the roofs of the houses behind the terrace (on the left of the view). By swapping the 'X' and 'Y' settings for one another, I was able to correct the error on one set of roofs...and re-create it on the other. And repeating those same settings for the walls only shows a very blurred image of the bricks.
Almost everything I know about Blender has come from the excellent Wikibook, Blender 3D: Noob to Pro. Unfortunately, its chapter on UV mapping, which I suspect is where the answer to this lies, uses the example of a 3D sphere. My walls and roofs are 2D faces, and when I try to open the UV Image Editor I get images of other textures used by the original modeller, but not the ones I'm using. If I am to use the Image Editor, I would need to understand what it means to mark seams on a 2D face when I'm hoping to avoid tiling on most of the faces.