Wednesday, 28 May 2014

Building Belah Viaduct Continued

Phil Baines talks us through the process of building the incredible structure that is Belah Viaduct:

The Building of Belah Viaduct - Part 2

  Having built the handrail, the next section to be constructed was the deck. The reason for doing the deck next was to do with the shadow baking. As the upper portion of the supports would be under the deck, it was necessary to have it in place to cast shadows on to the supports.
  As with any major construction it can be daunting looking at the project as a whole, so the best way forward is to break it down into manageable chunks. With 16 spans, each span becomes an obvious chunk and that is how I built the deck, in 61ft sections. The model would also be used for the Deepdale Viaduct. Deepdale is curved so I decided I would need to build it as a Lofted item, therefore, it made even more sense to construct the model in single span sections.
  The start was simple, an 18.9m(61ft) long by 7.4m(24ft) wide deck which was set with its upwards facing poly at zero in the modelling  software. The deck was set as ground level so that when the Deepdale model was attached to the track, using the Offset tool, it would be at the right height.
  With the deck in place, all that was necessary was to replicate the various supports and braces underneath. I would make one brace or support at a time, unwrap it, then duplicate it as required. I make a basic assumption that the light will fall on identical parts in an identical way, so unwrapping then copying saves a lot of unnecessary duplication of effort.
  Although it was decided to make this a high poly model it is still not necessary to model every detail of the bridge, so a certain amount of artistic licence is involved in choosing the elements to re-produce. The initial view of the deck span looked like above and the observant among you will note the missing elements.
  As can be seen in the above photo, the rails crossing the viaduct ran on top of wooden baulks of timber, so the final version of the deck span had these added, then the model was textured and shadow baked with the following result. I also modelled in a check rail while I was on with it.
  Next I made a start on the supports. There are 15 supports and each support is constructed of  5m high sections, ranging from 2 sections in the shortest to 11 sections in the tallest.
The construction starts with a single central column which is displaced 2.25m along the Y axis, and then unwrapped. The column is then copied and the copy moved and inclined to represent the side column, which is repeated for the other side. The UVW maps are then selected and moved to a clear area of the texture sheet, so, when shadow baked  they display the different shadows cast by their  different orientation.
  The three columns were then grouped together and the group copied and rotated 180deg around the 0,0 point. This orients the same polys to the inside of the section so I can use the same UVW map.
  Using identical techniques I then built up all the elements of the section, adding the various beams and braces until I had a complete section ready for duplication.
  You will notice the strange extensions to the cross beams, which were added to help me during the duplication process.
The duplication process was done in three different ways. Firstly the central features were simply copied and lowered by 5m. Secondly, the side elements were copied, lowered 5m then  displaced sideways by 0.45m so their tops lined up with the bottoms of the layer above. Thirdly, the cross braces were lowered then scaled to fit the wider cross section. This stretches the texture slightly, but on such minor items I considered it an acceptable compromise. I didn't think this would be acceptable for the cross beams, as they were much larger and texture stretching would be obvious, therefore, I made them long enough for the widest cross section, but with pieces I could chop off to fit at each level.

I then have a structure like this:
  As mentioned earlier, the top section is in the shadow of the deck span, so I now select all the elements of the topmost support section and move them on the UV map, then shadow bake both sections.
  All that remains is to duplicate the lower section 9 more times and I have replicated the tallest support. This is, in turn, duplicated 14 times to generate all the supports. It is then a simple process of chopping off unwanted sections to create supports of the right height, whilst trimming the cross beams to the right length at the same time and we are nearly  there.
  One further tweak is required. In this picture from the ©Turner collection it is possible to see the lower half of each bottom section was painted black.
 Whilst this was not a consistent feature over the life of the viaduct, it was decided to add it to the model.
  This was achieved by, once more, playing with the UV map. Having selected all the bottom section elements of the model, they were unwrapped and then their UV maps moved to a clear area of the texture where the black paint could be added.

  The main elements off the Viaduct were now finished and in my next blog I'll detail the final bits and pieces to get the viaduct in game.

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