Just an update on my experience with high res terrain mesh in the USA.
I've managed to get rid of the discontinuities / "cliffs" between adjacent 1 x 1 degree download areas by geoconverting a 2 x 2 block of them together, using a TMC file whose NW co-ordinates are the NW corner of the northwestern-most 1x1 degree area and whose SE co-ordinates are the SE corner of the southeastern-most 1x1 degree area. I put all the IMG files and their corresponding TFW files together in the imput_aerial_images folder. This eliminates all the masked tiles on the boundaries and pushes the problem to the outer boundary which can, of course, be as large as you like. The block could be 2 x 2, 4 x 4 or whatever.
I've also attached a couple of comparison screenshots below. They were taken on the Elwha River SW of Port Angeles, Washington State. The top one is with the high res terrain mesh and the bottom one is with the default mesh. Note in particular the ravine, which is completely absent in the default mesh screenshot and very well defined in the high res shot.
Hey Ian, this looks fantastic! Nice job, and glad you were able to figure out how to do it. It makes a huge difference in certain areas. One of the nice side-effects of this is that it also makes the satellite orthos look better, because they get properly stretched over the terrain shapes instead of being distorted over flat ground.