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rhumbaflappy

Lat / Lon and Ground2K

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First of all, I would like to congratulate Christian Fumey on this great program. I've also been working on a visual designer but you have progressed much farthur than I!I been experimenting with Ground2K and found it to be easy to use once you learn how it works. I've done some test scenery (of areas around Quincy, Ca) creating lakes, rivers, and roads. I've been using topographical maps that I have obtained from the USGS. However, when I create the scenery and then go into MSFS, I find that the objects I created are rotated a bit. This is very evident on roads and rivers winding their way through mountains. I'm using my West Coast source data for the elevations (which I've triple checked for accuracy, so I'm sure it's correct). But sure enough, when I get one end of a river exactly placed, the other end tends to be off. The longer the river, the worse the condition. So what's up? I think I found the answer.Ground2K only asks for two data points to set up the coordinates on you source graphic. In a way, we're digitizing the maps. However, to properly digitize a map, you need three coordinates, not two. If you use only two points, you will get a Delta-X and Delta-Y for the map. But the program will have to assume that the X and Y direction on the map is set up on an exact north-south and east-west line. In most cases this is not the case. Topographical maps from the USGS are based on a UTM grid developed in 1927 and utilizing the NAD-27 format. These maps are slightly rotated and thus the northern latitude on the east end is not the same as the northern latitude on the west end. So a third point has to be placed to not only determine the "height" and "width" of the map, but also it's rotation.Christian, your method of obtaining points is a good one, you just need to ask for a third point to adjust the lat / lon values for rotation of the graphic. This will also help set up an aspect ratio of sorts.To really see what I mean, here is a link of a topo map that has coordinates.[http://terraserver.homeadvisor.msn.com/imageinfo.aspx?T=2&S=12&X=843&Y=5538&Z=10&W=2&P=10+km+N++of+Quincy%2c+California%2c+United+States&D=01+Jul+1994&O=o40120a8&Lon=-120.9566&Lat=40.0093]Again, this is a great tool which will make MSFS a much better product then it already is. Lee Steffensen[www.FSGenesis.com] Home of the West Coast and other great scenery for Flight Simulator.

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Hi Lee.The problem is more profound than a simple rotation. The geographic projection is conic, an as such, it has a perspective-like tipping to the north.What we need is a freeware source for reprojection to an equidistant-type projection... like the DEM data or landclass data we use.There is a solution I'm working on.http://www.pcigeomatics.com/product_ind/freeview.htmlFreeview is a viewer... it doesn't save anything, although you can take screenshots. Freeview will "read" an amazing variety of georeferenced formats, and allow you to use a crosshair to find exact coordinates of points... like the corners of our images for Ground2K.If you load a world basemap, that has the correct projection we need for Ground2K, whatever georeferenced layer we then add can be reprojected to the basemap's projection!I have such a world basemap as a shapefile:cntry94.zip Ths is from ArcExplorer's tutorial. It is a world map of the projection we need.I can load a DLG or DRG file onto this basemap, and I can then reproject it to the proper format for Ground2K... a screenshot does the trick, after I jot down some corner coordinates. =============Freeview also lets you combine many types of images... you can start with a basemap, add aerial photo, then place DLG, shapefiles, EOO, whatever on top of the photo ... and it is all reprojected properly, ready for a screenshot and Ground2K!Dick

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Thanks Dick!I agree with you. Being a programmer, sometimes I think everything should be handled with code. But you got me thinking and I now geo-reference the topo maps with a GIS program that Justin Tyme recommended to me. The program is Manifold and works great for this type of work.Lee.

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Hi Lee.I remember Justin highly recommending that program. I'm glad it does the trick for you.I see that Manifold has scripting capabilities, and apparently can interface with Visual Basic. That presents all kinds of possibilities for VTP and LWM generation.Dick

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