I've been working for the past week on trying to build a route, based on the the old Tillamook Bay RR. I have purchased ReDem and RWDecal, and did a lot of reading here and online. I decide to start in Tillamook Oregon and run up the coast north to Wheeler and then to Mohler, following the original trackage, on in to the BN yard in Northwest Portland. I laid out a path in Google Earth , fired up ReDem and created the texture tiles, then got going in RWDecal. Went to start laying decals and noticed that everything was FLAT as a pancake! Upon closer inspection, I found that I had entered -122.80328 as my starting lon instead of -123.80328 
Ok, nuke that route, good thing I bought RWTools too! Restarted from scratch, using the right starting coordinates. Rerun ReDem, copy the terrrain files over and have a peek, whooopie! there are bumps and hills, well not that many at the starting point, it is pretty flat in RL. Run RWDecal in create all files (make a whole route) mode, using 1/3 arc sec bil files. Start laying decals, just started at the yard at the Port of Tillamook HQ, and just laying down the decals that have track to get a feel for it and maybe start laying a bit of track. So I get about a mile up the way and the decal I'm laying has the track crossing a small stream (actually a drainage ditch) on a bridge. It seems odd that where I'm putting it is pretty flat, but I don't know how deep these ditches are, so on I go. I get to the NEXT decal chunk marker,, (I'm using chunks, and using the center markers to line them up), and notice that there is a depression in the terrain, kind of shaped like the image of the the ditch in the decal I just placed....HUMMM! 
So I figure I' must have screwed up and put the wrong decal chunk down, so I look at the center marker and it says, 0013 X2 Y2 Center (well it really sez Centre, but my spellchecker says that's wrong LOL). So I grab 0013 X2 Y2 decal and plop it down, no stream in this one 
!! I delete that decal and put 0010 X2 Y1 down instead, yep that's the one with the ditch! takes a LOT of jockeying around, but I got it to line up perfectly with the image of the ditch and the actual terrain ditch. Only now the decal chunk center is nowhere near the little flag center marker.So bottom line is either the decal markers are too far south and west, or my terrain features are too far north and east!
I'm about to tear out the rest of my hair, and go back to playing World of Warcraft.
I have found a few things out though... when you go to Google to download GoogleEarth, they will by default, give you 6.xx BETA version. This is fine until you try to use RWDecal and follow the youTube tutorials, You won't get the little cross hairs in the center of your screen and there's no pretty red box either. I spent a long time trying to figure out how to turn them on until I noticed the "beta" in the about GoogleEarth. Uninstalled the beta, went back to google and found the RELEASE version 5.2.1, and now it works fine.
The other thing that has me puzzled is, when I download the data files from usgs.gov, I usually pick the 1/3 arc sec files, I just did another test run and this time I picked the 1 arc sec, the 1/3 arc sec and the 1/9 arc sec formats. In the 1/9 arc sec zip files there are 2 .bil files! they are both the same size, and when I run them through ReDem I don't get any more tiles from the second one! IE I run 123456.bil file and get 158 tiles, then I run ReDem again with the second file 123456-2.bil , ReDem doesn't create any new tiles, if I do it the other way, and run the -2 file first into a different directory I get the same 158 files.
Any help, suggestions, hints or offers of 15 year old single malt scotch would be greatly appreciated.
(wish all the tech support could be that good!). Any way, Jim told me how to restart where it left off. And I had also mentioned the decal vs terrain shift issue. He said it had happened to him, but it was a user error, cause by mis-entering the starting Coordinates.