how do I join dem terrain modules together?

[bandopacific]

Well, i've searched and searched google, and still no luck.
maybe I should've gone here in the first place.
I successfully created 2 separate "modules" from DEMS (thanks to the excellent tutorial

http://freepages.misc.rootsweb.com/...rrainGeneration/Computer-generatedTerrain.htm


They were created from adjoining dems (The Wheeling & Lake Erie in North Eastern Ohio USA) so the assumption would be that the two of the would fit together perfectly when merged. WRONG! They wouldn't line up at all, and there was a dreadful chasm in between.
I would love to expand this route - creating the individual modules was more fun than I have had in a long time - I even have the 1905 topographic map of the area

(St. Clairsville 1905) found at

http://www.railsandtrails.com/USGS1900/OH/index.html

So I can restore abandoned coal branches.

But my inability to join modules together is very frustrating
Someone help - please!

Lloyd
B & O Pacific

 

[geophil]

It depends on the tool that has been used for creating the DEM terrain. HOG does not enforce any alignment. It's completely up to the route builder to choose where to put the baseboard grid origin. If building more than one module it is most important to define coordinate-based borders.

Much easier with MapMaker or TransDEM. Both have a definite relation between baseboard grid and UTM coordinates (the map projection in use for all the tools). As long as in the same UTM zone MapMaker modules should fit together. Same with TransDEM. And, if setting the proper baseboard grid offset in TransDEM, new TransDEM modules can be merged with MapMaker. With a bit of experimenting this may also work for new TransDEM modules to be merged with HOG modules.



BTW, there is a little obstacle with these pre-1920 maps you are mentioning. Unfortunately, we don't know much about the geodetic datum of the maps. It's not NAD27 (which was introduced in 1927). Therefore, geo-referencing is a bit of an approximation.

geophil

 

[RPearson]

As geophil says HOG doesn't enforce alignment. It works directly from the image file you present it. Your DEM won't match up (height x width) with an exact number of Trainz baseboards so if you crop it to fit an exact number you lose part of the DEM and if you don't you end up with partially DEM'd baseboards on 2 edges. If you filter it in HOG it's any ones guess how the DEM is sliced up.

My advice to anyone doing this with MD/HOG is to merge the DEMs together in MD before you create the image or ASCII DEM and then crop the area you want to use. If you still want to make multiple layouts and merge them in Surveyor you can keep track of the pixel location of the crop lines and manage the alignment yourself. If the resulting image file from MD or Piglet is too large to work with you can section the DEM into parts in MD and work with them separtely thought this present some problems splicing images together where they overlap the sections.

Bob Pearson

 

[bandopacific]

Thank you geophil and Bob - it kind of looks like MicroDem plus HOG is doing it the hard way for a long route
And that brings me to my next question - how do you merge dems in microdem? Again i looked and looked with no luck

Thanks
B&O P.

 

[Dermmy]

'In-Out' (about half way along the top)

'Merge' from the pop-up, then 'DEMs'

Andy

 

[bandopacific]

Thanks Andy
I'll try it - I looked and looked in MicroDem and could find nothing
The more I see of Transdem the more I think that's the route I want to take

B&O Pacific

 

[bandopacific]

Well, I cobbled the 2 modules together - inserted a row of blank baseboards together and merged them - built a connecting track and fudged in the terrain.
Not the way I like to do things, but it came out pretty good nonetheless. I'm having a ball.

B&O Pacific