It may not seem like one would need it, but railway companies map their rails and surrounding areas fairly frequently. At first you might thing (like I do) that at this point they have it all mapped, but the amount of soils shift and initial survey error really require frequent resurvey. One way that rail companies are accomplishing this is mounting LiDAR systems onto locomotives and running them down the track. This provides a very accurate view of the area around the track. In some areas these LiDAR data sets can be some of the best digital terrains that you will find anywhere. One of the draw backs though is that you are limited to the line of sight of the mount on the locomotive.
So now my ham-fisted segue into today's article. An Australian mapping company used a UAV to map a portion of railway. The article has all of the details, but effectively they were able to show how a UAV can perform a survey at great accuracy and precision with low cost. One of the best features of the UAV that they used was that it was able to correct the data at the point of collection instead of the more traditional method of correcting in the office. I am a big supporter of techniques that use in field data correction because you do not have to budget and schedule all of the worker hours that would be required back in the office.