Tinian Island (Part 2)

[Guest]

I think I've solved the problem.The text file accompanying the dem had this line:Z_RESOLUTION: .100So I changed my scale (the last line) to read: ScaleinMeters = .1That seemed to do the trick.Now, all I have to do is to make some major changes to the coastlines. The whole island appears to be displaced slightly to the west.Phil

[Guest]

Hey Phil,Sounds like your going through the same process I went through with Yap. The Tinian data has its own coordinate system based on the Guam datum, so it won't line up with the MS data, which uses the WGS84 datum. You can shift your DEM data by changing your "LAT" and "LON" entries in your .inf file. (Note that this simple shift only works for small areas like pacific islands!) If you don't have the exact conversion you could get it from a reference point that is in both MSFS and on the Tinian map (like the end of the runway)- measure coord.s on both and then calculate the difference. Or you could just do trial and error.I'd be interested to see how the error on Tinian compares to that on Yap. Here is the 2D Yap conversion:Yap Astro 1965 to NAD83(WGS84):Lat add .001319444 degrees (145.9m)Lon subtract .0068263889 deg (749.5m)Good luck,andy

[Guest]

Andy,Sorry for not replying earlier. Just noticed this post and I haven't worked on Tinian for a few weeks.As I recall, it looked like MS has shifted the island a little bit to the southeast. Is it easier to shift the mesh to fit under the island, or should I move the whole island on top of the mesh?I am planning on making some changes to the MS shorelines and roads using Ground2K. Will that result in two BGL files? Can they be merged, either in the program or in MS? (I hate to have MS have to read too many files.)Finally, and this is a mesh question: I noticed that the runways on Tinian slope upwards about 50 feet. It appears that the best solution is to create a sloping area on the mesh itself and to paint on some runways. Any good programs for making small changes to meshes?As soon as I have time to get back to it, I will get you the exact amount of the offset and we can compare notes to see if they are the same.Phil

[Guest]

Hi Phil,I realize now how unclear I was in my previous message! The deal is that Microsoft hasn't moved Tinian - Your DEM data from the USGS is in the wrong datum to match up. As far as I can tell, the USGS folks think they converted all of their pacific island data over to WGS84/NAD83, but the data are still in their original coordinate systems! I have a digital version of the Tinian map, and it seems to have its own coordinate system, as does Yap. As I mentioned before, I am interested in seeing if the various island coordinate systems are related as far as the offset.Microsoft used data that is very accurate, but is low resolution. The coastlines are bad, but they are more accurately referenced to the rest of the world than the more detailed USGS maps of individual islands.To finally answer your question, your offset problem can be solved by changing the mesh corner coordinates, as I mentioned in the previous message. This is the easiest method, and will also be the most accurate. This is almost the only useful thing I know how to do as far as scenery is concerned, so I'll be happy to share any of my limited knowledge if you need any help.As far as your coastline goes, you will be forced to have extra bgl files, because there are multiple formats, and the bgl's have to be stored separately for different types of data. You will find that it doesn't impact the sim performance much. There are also some utilities availble on avsim for combining bgls, so you can possibly combine some later.I haven't tried ground2k yet, but it seems to be the tool you need.I used Coastline Maker to fix some of the Yap Coast, but I'm about to redo that work, and I am planning to check out ground2k this go around. The latest version appears to have some capability to adjust terrain with "flatten" commands, which is not the same as changing mesh. You'll have to look and see what it does.By the way, I'm not sure you will need to mess with the mesh for your airfields, anyway. Once you get your mesh lined up, the slope should be built in. They you can just paint runways on the existing terrain.good luck,andy

[Guest]

I thought you might be saying that the mesh was off, but was not sure. I have several digital maps of Tinian and, on one of them, the Lat/Long did not seem to line up with any of the other versions.I assume that it's going to be a bit tricky to determine when I have the mesh lined up- I would need some prominent landmark. (Now that I think about it, maybe the harbor would be the best place to look.)As for MS vs real life Tinian, you can see how well MS did by looking at my webpage: http://philcrowther.com/6bgmain.htmlGo to the "Tiny Tinian" page and there is a map where I overlaid a real map of Tinian over the MS version. I shifted the map slightly to obtain a "best fit". Otherwise, the whole island would be offset a bit.FYI, I also compiled the mesh for Saipan, but ran into some real display problems - mountains banging up and down. I had to get rid of it. Glad my Dad wasn't stationed there.Thanks for the advice. Let me know if ground2k works well for you in your project.