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Guest JohnC

Georeferencing a NAD83 Bitmap of DOQ's.

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When I looked for a way to georeference and match up my large (advertised as) NAD83 photoreal DOQ color bitmaps, I was never really satisfied, even when I used the UTM coordinates obtained from Topozone and converted them to Lat long extents. Then I realized that a constant Northing coordinate like 4500000 does NOT mean a constant Latitude in degrees/ minutes /seconds as you move East or West. If you go into Topozone on the Web and move from 630000 Easting/4500000 Northing to 640000 Easting/4500000Northing on a WGS84/NAD83 map you find that you go South from N40/38/26_W73/27/45 to N40/38/20_W73/20/40 in D/M/S format.That means as you move 7 minutes/5 seconds East, (10 km) at a constant Northing then Topozone says you move approx 6 seconds South even though the Northing value remains CONSTANT at 4500000. I conclude then, that large WGS/NAD83 bitmaps (that's what Topozone says "they" are displaying) cannot line up over larger distances with the orthogonal scheme FS9 uses, and that a 10000 meter wide bitmap actually has the RHS at a lower latitude than the LHS by roughly 6 seconds. Patch a dozen or so 30K by 30k bitmaps together over shorelines and strong mesh gradients and you soon find the errrors have added up and airport runways and other features do not line up very well (an understatement). (Which explains why I am tearing my hair out at this stage.)I am hoping someone can tell me I'm missing something, and/or there is some magic (free) fix out there. If I am correct, I need a program which can orthoganalize a WGS84/NAD83 bitmap into a FS9 friendly horizontal latitude/vertical Longitude map. BTW, this has implications for any application that you use over large areas if you use a background image in Ground2k for instance. Otherwise, I have to break the bmps into smaller pieces and that may just be the end of this quest for me.

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Hi John,actually, the NAD83 *datum* is almost identical to the WGS84 *datum*; the difference between the two can be ifnored even for large areas of coverage.The issue is with the projection: DOQQ and many other source maps or imagery use the UTM projection and it is this you need to convert to the FS-native lat/long projection (which isn't really a projection but let's no split hairs about that right now).The easiest way to do this conversion is with a low-cost GIS like Global Mapper or Manifold but not everyone has a couple of hundred bucks spare change for these (It depends on how you value your time, I guess). I use Global Mapper and love it!Anyway, people here and elsewhere have been looking for free alternatives and we did find and discuss a couple of options. Here's an elderly thread - http://forums.avsim.net/dcboard.php?az=sho...ing_type=search - though I'm not sure whether the tools mentioned are still available.Good luck.Cheers, Holger

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Nope, Holger, Scott Gridley pointed out a few months ago that ERDAS ViewFinder is no longer available at the Digital Grove. It can probably still be found (for example, at the GIS Caf

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Hi Holger (and the others kind enough to respond).....my source material on a CD is NAD83 but for some reason the UTM coordinates are not the usual ones..the extension is sid (which stands for slot id file), and they are 20:1 compressed (MrSID). So I have to work with a county size 50Mb file with the "wrong" UTMs, find a way to reproject it with GDAWARP and then redisplay/copy all the images in ArcExplorer(if ArcExplorer will even display the reprojected image file???).If the UTM eastings are not the normal ones I can't see how I could convert this with gdawarp to a geographic lat/long format. Enough is enough. I gotta move on here.

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Are you sure it is UTM, and not State Plane Coordinate System?scott s..

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Actually your question caused me to go back and read the product description more carefully.... http://www.vcgi.org/dataware/products/metadata/naip2003.htmand with a little more knowledge....it is in State Plane coordinates....which may (or may not) very well be 1:1 with Geographic Lat/Long/orthogonal data. However, the stitching together of the bitmaps I produced was very carefully done, and I am quite sure that over large distances there is some kind of drift in the data that makes it difficult to overlay my FSGenesis Northeast mesh when you have islands with steep gradient shorelines, etc. This product probably was not designed to require hyper accurate overlays over long distances (20km). The real problem here is that I am a perfectionist.}( I much appreciate everyones willingness to help. I will try to do thisin a piecewise manner after I take a break.

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Hi John,here's my suggestion: download and install the trial version of Global Mapper - http://www.globalmapper.com/ - (it won't expire but doesn't let you save your transformations) and load up your file.Use the Tools > Configure > Projection menu to change from the Vermont State Plane NAD83 projection to geographic WGS84 and you'll see that the two are very different indeed.You'll still have to find a freeware transformation tool but at least you can find out up front how much of a difference there is between various projections and whether your patchwork approach has any chance of succeeding. If you had a registered version of GM you'd simply save the appropriate subset of your image in BIL/BSQ format, copy the relevant parameters into your inf file, and compile with resample.exe.Cheers, Holger

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Hello Holger...I took a look at Globalmapper but have decided to pass...here's my reasoning.....my complaint (about my data) has to do with small drifts which appear over long distances which moves airport images out from under stock runways, rivers up the side of a mountainside etc. blah blah blahIf I create a 250 megabyte 50 kilometer image, I conclude that it is unreasonable to expect my as received raw data to be so well georeferenced that images of runways will line up with FS9 airport structures 25 miles (oops 40kilometers away..you're in Calgary right?). once they are projected in a different format.So the investment (the $ are not the problem) in time to learn another system for a one time scenery make few people will be that interested indoesn't seem practical to me....particularly if the as received data is not guaranteed perfect. When I come up with an easy way to output a pixel location from a latitude longiitude value I can correct the massive bitmaps I already have, by cutting and pasting in the same manner as a stained glass window is made. Paint Shop Pro has all the tools I need to do this.Thanks for taking the time to reply. PS I was a Canuck myself once....ex Montrealer.

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There is a useful freeware coordinate converter called CORPSCON6 for converting several formats including state plane coordinates. I have the entire state of West Virginia in 2ft to pixel on 10 DVD's Only wish I could learn how to use them. I like some others have trouble getting photo to line up with scenery.

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sounds bad. I have the entire state of West Virginia on SAMB files 38+ GB. If I read right, that two sid files make up one 7.5 min quad. I wonder if one could paste each two sections that make uf a 7.5 min quad use the quad coordinates and make the scenery. Any help greatly appreciated.Richard

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Hi Richard...I have the whole state of Vermont on a DVD but not in the resolution you have. It always seemed to me that one could "drag" each of the corners of a bitmap and with trial and error, and with a small enough map, match up a corner feature with its known coordinates with a GMAX 3D thumbtack placed in FSX at the "exact" coordinates from, say, Google. Or use the Google image(if it is good quality, to stretch your WVA image over the "not allowed to be published" Google image. Alas, my personal situation does not allow this expenditure of time.In Paint Shop Pro this dragging of each corner individually is possible with the distortion tool over a different image on a lower level. I hope Holger will see this and comment.

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My files are 5,000 5,000 pixel 24 Bit immages at 2 ft per pixel. I think I read earler that two immages make one 7.5 minute quad. I have PSP Pro and have sucessfuly pasted the files up to 5 x 5. The files line up pixel to pixel no uverlap. I get rather accurate coordinates using CorpsCon. I am just trying to find out what sizer I should make them. Maby someone will come up with something to simplify the use of state mapping file.Richard

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Richard I downloaded corpscon 6 and assume you did as well. When I try to unzip it I get "unexpected error. Check file access permissions. The installation wiill be terminated". Did u find a fix for this?

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Strange! I never had any problems downloading or unzipping. You should end up with 137 files and 3 sub folders. Geoid, Nadcon, and Vertcon. The compressed self extracting corpson_base_conus.exe is 6,238 KB. Richard

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