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"Attn: JohnCS, Coordinates"

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funnelfan (68 posts)
Jan-26-02, 04:11 AM (EST) "Attn: JohnCS, Coordinates" John, just wanted to see if you had noticed a slight problem with the coordinate system in MSTS, and maybe if you had some insight into the reasons behind it. Backgound first, I'm working a on a part of my route that feature meandering spurs and street running trackage. But nothing seem to line up right, but for the life of me I couldn't figure out why. Finally I erased everything from the area, including the parkers I put down. Next I put down a whole set of new markers, this time laid out in a grid pattern with a marker at every street intersection. Ah there's the problem, MSTS's coordinate system is not square. While the Latitude lines are square, longitude lines are shifted toward the northeast by as much as 30 degrees! I'm pulling my coordiantes from Delorme's Topo USA v.3.0. On that program the grid pattern of the streets is laid out to the exactly to the grid lines. Not sure what the MSTS coordinates are laid out too. But I do remember that you initially had some troubles with the coordiantes when you were first working with DEMEX, could you share what you discovered?ThanksTed Curphey
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Subject Author Message Date ID RE: Attn: JohnCS, Coordinates JohnCS Jan-26-02 1 RE: Attn: JohnCS, Coordinates wbgx Jan-26-02 2

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JohnCS (257 posts)
Jan-26-02, 12:59 PM (EST) 1. "RE: Attn: JohnCS, Coordinates" Well see, the earth is kinda round (almost eliptical really), but the dark ages still rule in MSTS land because there its flat. The problem is you can't take a flat plane and wrap it around an ellipse without wrinkles and tears (just try it).So MSTS uses what is called a Goode Homolosine Projection, which is the map which you see in the RGE. The two advantages of this projection is that a) all discontinuities are mapped to water bodies, which is kinda nice so you don't end up with the grand canyon in the middle of Iowa, and b) it is area-preserving so that two points a mile apart at the top of the map are the same distance apart on the map as two points a mile apart at the center of the map. To accomplish these two objectives however the projection is not angle-preserving - thus two vectors on earth at 90 degree angles will not be at 90 degrees on the map.You can contrast this to the UTM projection which USGS uses. This is an area and angle preserving projection. However there are 60 goures <sic> instead of the 5 or so in Goode, and these fall on all kind of land masses. You can merge data from two adjacent UTM zones without much difficulty and fake it, but try merging 3 zones and you get all kinds of nasty distortions.Here's a DEMEX image showing how the tiles project onto a UTM projection DEM in Wyoming.
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wbgx (122 posts)
Jan-26-02, 10:54 PM (EST) 2. "RE: Attn: JohnCS, Coordinates" It took me a little while to figure out the graphic you included in your post, but I have the picture now. Thanks for the insight.Boomer Remove | Alert Edit | Reply | Reply With Quote | Top

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