How Crossrail was affected by the curvature of the Earth (2018)
Funny, I was just reminiscing about this very problem this afternoon.<p>When you are working to specific locations at each end it is a really tricky problem, but local grids like the ones described here help. I&#x27;ve worked on rail projects for mines in remote areas that need a few hundred kms of new track and span across &quot;zones&quot;. The problem is exacerbated (at least then, early 00s) by the way you represent these in various CAD products, especially when sharing data between them. There are two main 3D modeling kernels that most popular professional CAD products rely on, both from the 70&#x27;s 80&#x27;s with minor updates neither 64bit native. Why is this an issue? Well, you see, the standard for civil design is to model in &quot;real world&quot; coordinates. That means you could be dealing with a file at the resolutions of mm for engineering purposes, but thousands of kms away from the origin. Now we enter the world off floating point calculation errors and subsequent kernel issues.<p>There are ways around it. Essentially offsets that move the origin of the file temporarily with a note to itself that everything must also account for the offset before displaying in the UI. But it can get confusing, fast, every product does it its own way and may not recognise this trickery. Working digitally with sparse real world reference data of varying qualities can be a big risk. I remember being in a large workshop with two surveying companies, our client and some civil engineers. I was horrified that I knew more about the various grids and their issues than any one else. I did one unit of surveying at uni, not long before and had to do a lot of research to get my head around the issues. These people were meant to be the experts.<p>The good thing about linear projects is that on those scales you can usually get somewhere where you can &quot;work it out&quot; on site (i.e. fudge it to make it fit). But It potentially affects everything, like, how many meters of track are we ordering? What contingency do we need? What are our expected mass haul volumes and estimated fuel costs? How big should we make our margin of error? It&#x27;ll all work itself out, it&#x27;ll just cost.<p>What happens when we start building beyond the planet and need to accomodate for curvatures in space time? Even ones that are brought about by the very thing you are building?