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Large Scale & Small Scale Scenery Sync?

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I am using ground2k and FS Scenery creator (FSSC)..For small scenery areas (typically an airport) I use FSSC. For the larger surrounding area I use Ground2k - roads, rivers, elevations and landclass. Unfortunatly many of the features of FSSC (particularly macros) are not available in Ground2k. While I can use a larger background template in FSSC to encompass the wider area it is not physiaclly sync'd with Ground2k. That is, to begin with Ground2k is not 100% accurate when using a background aerial photo. However, it is very close. The same thing applies to FSSC. The small errors in each adds up to a larger error when viewing FSSC macros near roads created by Ground2k. Since there is no current evidence that FS2004 will have more accurate roads, rivers and elevations the need for accurate modification remains but so does the ability of placing macro landmarks for VFR alongside the roadways and in towns.Perhaps the Lago FSSE upgraded system for FS2004 will be the answer by offering more and improved objects that satisfy the need for landmarks to aid in VFR.Dick

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Hi Dick.I have written of this before.FSSC ( and Airport ) uses maps of Orthographic projection.Ground2K uses maps of Geographic projection.If you use a map of the right projection, with the right program, both programs will place their scenery with amazing accuracy.I've been using maps from mappoint.msn.com for some experiments. The maps are Orthographic or equidistant ( distances measured in meters ). They work very well with FSSC and Airport.I also can use ( for much of Europe ) DOI 10 meter images ( Digital Orthorgaphic Images... a misnomer ), from the Geospatial Engine.These aerial images are not really suitable for CUSTOM scenery, but they can make good map material for Ground2K, as they are already Geographic projection ( measured in decimal degrees of lat-long ).I can reproject the downloaded mappoint maps to Geographic ( or reproject the DOI to Orthographic ), and the images will line up exactly. Roads, streams, lakes... all alligned correctly.I believe the Mappoint maps ultimately may have used this DOI imagery as a basis for creating the vector data of the maps.==========================If you use the wrong maps, with the wrong programs, you'll soon find your scenery out of whack. And the larger the area, the more out of whack it becomes.Unfortunately, programs which can reproject raster images are expensive ( $300 US minimum... and can go into the thousands ).Sometimes an image can be 'tilted', or skewed in a paint program to compenate for the distortion, as a "dirty" way of reprojection.But for areas less than .15 degrees lat-long, or say, 3000 x 3000 meters, the distortion is not too bad. The trick is to use several maps of smaller areas, rather than to try to combine them into one large map.If you make several small VTP/LWM BGLs, and they don't line up, you can load them into TMFViewer, and use a screenshot of that for Ground2K, to rebuild them. I used screenshots from TMFViewer to rebuild the LWMs for the default Prince Edward Island, using Ground2K:PeiFixThe LWMs line up very well, because TMFViewer is in Geographic projection.There are programs that can use vector ( GIS ) data and create images of the right projection... the most familiar might be Terrascene, for FLY designers. We can use their images as maps for Ground2K ( or for CUSTOM scenery ), as they are Geographic in projection. But Terrascened images won't work well with Airport or FSSC, as the projection is wrong... and trying to allign a bitmap with the wrong projection doesn't work.Likewise, Airport and FSSC both place objects exactly on the correct lat-long-altitude point. The background map needs to be Orthographic, and orientated to true north ( or compensated in the program ).The only problem I have with FSSC's background usage, is that it uses a form of antialiasing that blurs closeups badly. The cure is to use a large map of a small area. BGLs can be merged, or the SCASM code preserved and combined, if having a small number of BGLs is a design goal... although I don't think lots of small BGLs are a problem for a project.Dick

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Which version of Airport are we talking about here?. I have used Airport for several years an never knew it had that capability.ThanksJoe W.

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Question on MapPoint:I cannot find the lat/lon of the extents of the displayed map?? I believe that these are needed for Ground2K.Another question:When you say Geographic Projection is this the same as Mercator, or Tranverse Mercator??Finally, I do now recall you covering these points before. One of the liabilities of a loosely organized set of libraries. Rather like an archeological passage of time but compressed to "internet speed" where data is quickly lost to time. We "dig" with searches but, as in the physical dig, you have to have some idea where to start digging.Need to become more familiar with cartography. Amazing the dozens of projections that have evolved for various needs. If you can not visualize this ain't for you.Dick

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Hi Dick and Joe.First off, Airport ( and FSSC ) can display any image as a background... and if it's a "good" image with the proper coordinates, they display properly.mappoint.msn.com can make very good maps... but we need to specify the exact center and an "A" value:If I type in a search for Delavan, Wi, under North America, I get an image of my home town. I use a large image to display it. I then zoom in a couple of times, to see the streets as fat white lines.Above the map is an icon to click for sending the map via e-mail. Click it, and look at the URL:http://maps.msn.com/map.aspx?ID=27CiJ.&C=4...c+United+StatesThis can be cut down to... :http://maps.msn.com/map.aspx?ID=27CiJ.&C=4...&A=12&S=800,740or even:http://maps.msn.com/map.aspx?C=42.62781,-8...&A=12&S=800,740I will save this url as a text, and then use it as a basis for generating URLs of any area of the world.S is the size in pixels for the image.A is a code for the span of meters per pixel 12 = 6.25m/pixel ( for Airport, we need (100/6.25) or 16 for a span ) 25 = 13.5 ( Airport needs (100/13.5) or 7.4074 for a span ) 50 = 27 100 = 54 150 = 81C are the lat,long coordinates of the center.You can save the map image as a GIF, then convert to a bitmap in a paint program. You can use this map as is... it is already orthographic in nature ( equidistant, measured in meters )... the datum is WGS84... perfect.You can alter the "A" and "C" codes to scale and orientate the map to many areas of the world. Europe and North America have decent maps, with the rest of the world as rougher data.========================================A tip for FSSC. Under the 'Tools...Preferences...' menu item, untick "Display Fractional Minutes" . This allows finer placement. Even so, FSSC will sometimes move the refpoints of objects 1 or 2 meters... and doesn't allow placement to fractions of a degree. I don't know why it does this. Airport doesn't seem to suffer this problem of arbitrary "rounding". The code can be changed in SCASM, and recompiled if accuracy of under 2 meters is desired.FSSC also will blur the zoomed image while Airport does not.=========================================Geographic projection is called by many names. "none", "lat-long", "equiangular", "geographic", "simple cylindrical".... The point is that it measures distances in decimal degrees, not meters, and all lines of latitude are horizontal, and all lines of longitude are vertical, and they cross at 90* angles. This is not true of orthographic, as the span between the lines of longitude narrow as we approach the poles.Top-down screenshots of FS ( easily seen when using cellgrid ) show this narrowing as we travel to the poles... orthographic ( FSSC or Airport ).Screenshots of TMFViewer show no narrowing... geographic ( Ground2k ).=========================================I have a copy of Global Mapper, so I can geo-reference images, then reproject them from orthographic to geographic. They fit perfectly into Ground2K. With this routine, I can get a very good coordination between Ground2K and Airport, my usual combination.I've found mappoint images, once reprojected properly, will fit aerial DOI images very close. And good vector data will also fit to these downloaded maps.There are no freeware raster reprojection tools of which I am aware. Perhaps GRASS will do it, but I never got that program working. I've heard it is quite complicated to operate.Global Mapper is a relatively cheap way to go for payware, but it will still cost $179 US. This also gives you some vector capability, with editing, and the ability to save data across several types, as well as creating georeferenced images of both raster and vector data. The ability to reproject images is it's selling point...most other raster reprojection utilities cost thousand(s).What to do for freeware?As I outlined in the above post, large maps of small areas will have less exaggeration of the differences in registration at the edges of the map. Each map has an absolute center-point.I think FSSC would even allow more than one map at a time ( not sure of this ). In any event, there's nothing wrong with having a scenery project composed of several BGLs from different Airport or FSSC projects, derived from different maps. Also, some paint programs will allow you to tilt an image... allowing you to compensate for meter-based maps that have a narrowing of longitudinal spans. But this probably is unneeded for the small areas like the "A=12" mappoint map.And Airport does seem to have a "finer" placement of objects, whereas FSSC seems to have a mind of it's own at placement under 2 meters.Airport, FSSC, and Ground2K can all be quite accurate with the right map. Ground2K is limited by the approx. 4.8 meter/pixel limitation of the sim for LWM and VTP. FSSC does need a coding change to eliminate what appear to be rounding errors in the finer placement of objects. Airport is just about dead-on for placement.Here's a pond, with an island and a building, made using the above maps. Ground2K properly placed the pond, Airport properly placed the building. ( I didn't tweak the code... this is how it came out ) :http://forums.avsim.com/user_files/22498.jpgDick

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Hi all.A follow-up to that long-winded reply. :)Many designer's use aerial images from terraserver-usa.com ( the MS terraserver site ).These images are orthographic, but the projection is UTM ( the info icon gives that information ).What is the difference between a basic orthographic and UTM?UTM image:http://forums.avsim.com/user_files/22500.jpgBasic Ortho reprojection:http://forums.avsim.com/user_files/22501.jpgNote the rotation of the image needed to make it fit Airport or FSSC properly as a basic ortho image. There might be some skewing involved as well a rotation. A similar rotation is needed for a geographic reprojection, if the image is to be used for Ground2K or for resampling CUSTOM. This is why these images are sometimes "off" when using TerraBuilder.Sometimes, elevational data is also not in the right projection, which results in mesh being "off".As you can see, this is actually a greater problem than the differences between ortho and geographic... in the case of TerraBuilder, you need to tilt and rotate/skew the image to get it to fit properly, as it needs to be geographic projection.Dick

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A simple THANKS for a most comprehensive reply!Dick KLBE

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Hello Dick (Boley, but hello to Dick Ludowise as well),Perhaps there is a simple solution to this problem.I have just recently completed a large project of most of the Gulf coast of Mississippi using Ground2K and Flight Simulator Scenery Creator.In Ground2K, I created the corrected coastlines, highways and all major roads, bayous, rivers, lakes, streams, forests, land and water class (following the Ludowise method of using an aerial image and filling in the features).I then precisely placed around 3 dozen custom objects using FSSC. I did not even bother with a background image, but simply got the coordinates in Ground2K and placed the objects in FSSC using these coordinates. (Note that you can change FSSC coordinates to degrees:minutes:seconds in the Preferences menu.)Since I was using the coordinates of the new terrain in Ground2K, all objects appeared in Flight Simulator exactly where I wanted.One caveat: FSSC seems to change the FS config file in order to show the new format of coordinates, so you will see FS coordinates in degrees:minutes:seconds unless you change back in the FSSC Preferences menu.Perhaps this will give you acceptable results.Best regards.Luis

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Thanks Dick... That was very detailed... Now if I can just figgure out what you mean on this and what scale I need to use in airport and Ground2k to get everything to match... My next scenery might be even better.. It's Fall City, Washington... But I gotta redo the river.... ThanksJoe W.

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much appreciated information, Dick. Over the years several folks have discussed these differences, but this was the most helpful, as you related the different projections to the tools in use. Experimentally, I've arrived at the need for a rotation of my image from terraserver-usa.com to fit the ms location of runway angles. Now you teach me that a screenshot of fs produces an othographic (but not a utm projection) .. this rotation you showed in this post is therefore exactly what I've been compensating for by rotating my terraserver image.Nice to know why! Of course, now I want global mapper...:-((Have to save my pennies.Now before I go, a teaser...I take a UTM projection ortho, and lay it into fs. Two airports of interest in the photo, seperated mostly horizontally by 5 miles. Rotation angles required to "undo" the utm projection appear to be different for airport one and airport two.Does this make sense to you? Perhaps the projection angle is only perfect at a point (perhaps a center point), and therefore a "conversion" from utm to not utm is only precise at a point, thus significant errors could occur when a good measure of precision is applied on either end of an image? Bob Bernstein

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Hi Bob.http://www.adit.co.uk/html/utmgrid.htmlA pretty good explaination.UTM is measured in meters, but all measurements are from the UTM grid lines ( which are separated on the earth by 6*.A true orthographic would have the meters measured from the center lat-long of each particular image.UTM is a way of standardizing the reference points. It is measured in meters, but the center of the image is not necessarily alligned north and south ( as would be a true orthographic ). UTM is measured in meters, but all measurements are from the UTM grid lines ( which are separated on the earth by 6* ). So UTM will have large EW distortions as you move away from the grid reference meridian.NS distortion, or skewing, is something I'm not sure about, but the reprojection to orthographic, by Global Mapper, seems to bear this out... unless Global mapper is somehow not reprojecting the UTM correctly.=======================This terra-server page does show neither the lines of latitude or longitude are parallel ( Lambeau Field, Green Bay, Wisconsin ):http://terraserver-usa.com/imageinfo.aspx?...974&Lat=44.5146Airport or FSSC would require a central lat-long as the orthographic center of the map, and the central NS meridian pointing to true north. There is a feature to accomidate magnetic deviation in the programs, but I don't know if we could use that to allign the UTM maps so NS was exactly vertical, in those programs. Does that make sense?Dick

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Dumb question but better safe than sorry.Assume a squared grid is superimposed atop an image/map. If I measure a latitude value on one of the grid line on the left side of the image and then measure the latitude on the same grid line on the right side of the image, and find them different, is this evidence of an orthographic or conical projection?I used the JM cox Terraserver "compositor". This program can assemble large amounts of Terraserver images into a wide area composit. He provides a grid and the described process occurs there same as is evident on your Terraserver image example. Just want to make sure.Seems to say, as you pointed out, smaller images are better since the orientation errors at the edges are reduced.Dick KLBE

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Hi Dick.Here's a graphic:http://forums.avsim.com/user_files/22738.gifThis explains how conic is more closely related to Geographic, as it's bounds are in lines of latitude and longitude ( expressed as degrees ). When reprojected, a true conic should fit exactly to Geographic. A square image of a conic projection can have what appears to be parallel latitudes, because the east and west corners are the same... but latitude dips in that projection, and the dip is cutoff by the squaring of the image.http://forums.avsim.com/user_files/22760.gifThere are other projections as variations of these types, and all were developed to take out visual distortions we note when trying to see a spherical surface on a flat 2-D plane.The sim is based on a Geographic projection of WGS84 datum. Airport and FSSC are actually trying to force a measurement of meters on this projection. BGL code also sometimes switches from measurements in degrees to measurements in meters... for example we can place a runway at a lat-long point, but we then express it's length and width as meters... and the sim's scenery 'engine' translates the runway for us.Generally speaking, all objects and effects are expressed as meters ( or scaled from that ), and all placement is in degrees. LWM and VTP are textures that are stretched between placement points... and are never expressed as distances.In a way, it's too bad we don't have a GUI object placement program that uses Geographic measurement, and backgrounds of that type. ( I don't think any are... but I could be wrong ). Instead, FSSC and Airport ( and others ) are in a true orthographic state. Ground2K may eventually allow placement of effects and objects.. it already can make night-lighted roads with SCASM code. Airport is leaning towards allowing VTP and LWM code. Eventually, we may be able to use one map projection type, either geographic or orthographic, and not worry about the differences, as the programs compute placement. Then the type of map would determine which program to use... unless one of these programs evolves to allow you to chose the projection as meters or degrees, before you load the background.Our major problem with background maps is that we have no low-cost or free method of reprojection for these images. And as you mentioned conic projection, it would be very hard to "fake" that reprojection with a paint program.But the rule of thumb is, large maps of small areas, and watch for rotation with UTM images. I think Paintshop Pro 8 allows a finer degree of rotation than we had before ( ? )Dick

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Once again thank you for the extensive info. The understanding of the elements are quite clear now. Maybe you could offer a reprojection service to recover your costs --- JUST KIDDING!!.Since Microsoft has not improved the placement of roads, rivers, etc. in 2004 programs Ground 2K remains a necessity for VFR flyers. Thus the need for a proper understanding of the limitations of Internet sources, as they relate to the program, are needed. I was initially enamored with Terrserver pictures as composited by J.D, Cox's program. However, I now find that Topozone also offers excellent maps with coastlines, rivers, lakes, and roads. Also railways if MS did a proper job with them. The info is about 10 years old but roads and rivers don't move that often! Until your explanation I wondered why I could never match one Topozone map background to the adjacent map. Always off by many feet/meters. I was so happy that the maps were so large but now I see that is a liability. Maybe Christian can do some math to reproject some popular sources for Ground2k use. He originally envisioned it for samll detail areas but it is being used (by me at least) to correct larger expanses such as the Great Salt Lake in Utah whose coastline is miserably defficient and roads/rivers traverse hillsides with abandon.Dick

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