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"XYZ File Adjustment Utility"

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wesdowns (155 posts)
Aug-25-01, 06:05 PM (EST) "XYZ File Adjustment Utility" How much demand is there for a utility that would offset the XYZ file to correct alignment problems from old source data? What additional features would you like programmed into it? Although my area has really precise data, I know that others seem to have problems with the markers and the DEM data not lining up. My research seems to indicate that the DEMs may be off by as much as 100m, and in some places, the markers may be off.Let me know what you want and I'll try to set up a utility to help you. Alert Edit | Reply | Reply With Quote | Top
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Subject Author Message Date ID RE: XYZ File Adjustment Utility lrperkins Aug-25-01 1 Multiplication of error..... wildh0rse Aug-26-01 2 RE: Multiplication of error..... wesdowns Aug-26-01 3

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lrperkins (79 posts)
Aug-25-01, 08:12 PM (EST) 1. "RE: XYZ File Adjustment Utility" Would this account for markers being off some? I've been using information from TIGER data. The markers from that data seem to be right on target. The data from the USGS site was off. Is that due to the Dem data being off?To answer the question, yes, a fix for that would be great.Lonnie
KRNO
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wildh0rse (178 posts)
Aug-26-01, 08:46 AM (EST) 2. "Multiplication of error....." Aha! So that's wahts going on. I guess, wes, by using the wgs84 datum I got a *more* accurate placement of markers, but still off by ~30 meters in N & E placement.If the data are off, that's one thing because you're just reproducing the same error if your extracting. But it seems that there are errors introduced by the extractor. It must be quantifiable, because in the last 3 extractions (for the same route) the markers show up in the same position.Could you direct me to the site you got this data (markers) from? I'd like to have a look. OH -- yes, Wes, I'd find that utitlty very useful, please post it! Remove | Alert Edit | Reply | Reply With Quote | Top
wesdowns (155 posts)
Aug-26-01, 01:03 PM (EST) 3. "RE: Multiplication of error....." LAST EDITED ON Aug-26-01 AT 01:05 PM (EST)The original source for the Marker data was the U.S. Bureau of Transportation Statistics rail database. I don't remember the URL (and have blanked out my web browser at least once since that time) but a search should turn it up. When you get to their site, just search for railroads and I think it'll turn up.The markers are stored in degree format, and therefore seem to be absolutely correct (when the original quatrangle map was correct--I've found two places on my route so far where the track pattern didn't match up with data from Terraserver aerial photography). Since the DEM data for 90% of my route was stored using the WGS84 datum, the markers and terrain seem to match perfectly.The biggest problem I had with the DEMs came from the fact that MicroDEM won't directly merge two DEM files with different datum values or different resolutions. Using the resample feature to "alter" the data worked well enough for single DEMs, but when I merged the results, I got distortion and gaps. The XYZ Merge utility was the answer, and all of the gaps and distortion seemed to go away. When I get track to Atlanta (that's the place where the datums varied the most), I'll be able to see more clearly if there's a spatial disparity on the resulting data.There are a couple of facts that will help me write a utility that will "straighten out" the XYZ files to align with the markers. First, is the distortion absolute, linear, or nonlinear? For example, if I'm off 30m W at the bottom of the map, how far off am I in the middle and at the top? That question has to be answered for both north-south distortion and east-west distortion, because the answers may be different. I can write the utility with controls that will allow different types of terrain stretching, but I need to know more information about the problems that people are experiencing.What would be very helpful is a measure of the X and Y distortion at each corner and center point of your map. There would be nine points to consider, marked with exclamation points below:!....!....!
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!....!....!Although the results would not be perfect, the correction should get the resulting XYZ file within a meter or so of alignment with the Marker file. Remove | Alert Edit | Reply | Reply With Quote | Top

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