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PanosG

creating coastlines

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Hi,I have an island mesh (LOD10) created from SRTM 3ARC data. The island covers approx. 3 cells. Now I want to create a coastline. I prefer to use Ground2k4 but I think that other tools will have similar results. First attempt was to use source SRTM data as the background bitmap, result is so imprecise that cannot be used. Then I tried to read mesh bgl (just one cell) with lwmviewer and export it as a bitmap, result was again very poor. The only method that seems to work is to follow the invisible coast in fs9 and transfer the movement as a line into Ground2k4. It's very slow process full of returns, few hundred meteres take hours.I also tried to create a huge polygon in Gmax and place it under the island (agl=false), I thought it can help to see in fs9 where exactly the land raises fron the sea, it again doesn't work. Visible boundaries between the polygon and terrain follow approximately area boundaries.What is the preferred method to create a coastline which follows the mesh.thanks for an answer if anybody has onejirpe

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Haven't tried this, but I think autoASM, sbuilder, and or slartibartfast may work better for this. In my case, I was able to get coastline data in ESRI shapefile vector format which can be converted for use in sbuilder.scott s..

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Hello Jiri (?),You are right, it can be difficult to draw new coasts without the aid of accurate and detailed topographic maps. I too have this problem. The following is my solution, but others may use different methods for this problem.It is easy enough to obtain maps through the internet, but they are neither very accurate, nor in the correct map projection for Flight Simulator, and they do not have latitude and longitude lines for alignment.No problem. I export a bitmap of the mesh with LWMViewer and then place the map over this bitmap in such a way that it covers the mesh. Then, I draw the new coast in Ground2K4.Some points of interest: When exporting a bitmap in LWMViewer, it is probably best to change to colour (from grey) first, since this gives a more legible bitmap.Placing the map over this bitmap will, of course, require re-sizing and perhaps even rotation in order to get it to fit. The larger your coast, the more difficult this will be. But, if this happens to me, I break up the map in pieces and place each over its part of the mesh image.In Ground2K4, there is a very handy function called "Coastline" that will easily allow for drawing new Water Masks by simply tracing the shape of the coast. What it does is to draw a shoreline and then fill the other side with a Water Mask for the extent of that Area. Very nice!There are some small problems, though. I have never been able to get the Coastline to join up from one end to the other. For some reason, it just will not calculate correctly and will not be created. So, between the beginning of the Coastline and the end, there will be one Area that is not covered. No problem - just draw a Water Mask there outlining the coast and extending to the boundaries of the Area.Also, this Coastline function does not like two lines in proximity, even if they are 2 or 3 Areas apart. One of the Coastlines will create a Water Mask that extends over the other one, placing water where there should be land. No problem - there as well, draw a Water Mask as above.For my part, I do not like to place beaches everywhere on my islands, since this is not realistic. So, I make the shoreline width only 2 meters wide (it does not display in the game) and choose one without waves or surf. Then, I either draw the real beach later where it should be, or draw a reef polygon and add an invisible beach there with waves or surf.Here is how it looks in Ground2K4 with the maps overlaid on the mesh bitmap:http://forums.avsim.net/user_files/128529.jpgIn this image, the background is removed, and you can see where I have drawn a Coastline, and where I have had to draw a Water Mask covering the entire Area(s):http://forums.avsim.net/user_files/128530.jpgThe results are pretty good, considering that I do not have accurate topographical maps. This is the default island of St. Thomas:http://forums.avsim.net/user_files/128532.gifAnd the modified coast, showing a very nice fit to the mesh:http://forums.avsim.net/user_files/128533.gifOnce the new Water Masks are finished, I create a new project in SBuilder, append the default HP file, delete the appropriate Water Masks in there, then append my new version. All that is left is to save the bgl in order to have a nice replacement for the default HP file.Undoubtedly, other methods exist, and if one can obtain good maps, then much of this is not necessary.Best regards.Luis

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IIRC that method relies on TerraScene, which in turn gets its data from USGS DLG files from SDTS. So I'm not sure how it would work for areas outside of the US :( Maybe it could use SRTM DEM data though, in which case I guess that is something to consider. The manual for TerraScene talks about getting shapefile format data from DCW -- but I don't think DCW is much better than what's in FS9 already? scott s..

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Mostly not. MS infact uses the DCW stuff I believe. In some areas that was dumbed down even further for MSFS (at least in FS2000, when I actually checked this). Also, DCW comes from different sources and you can get 'nice' effects like roads running in the water because the datasets have large errors and aren't compatible. If you want better data you need to speak to your responsible local government agency or even your local council. They have stacks of neat data, but usually you need to pay $$$...Cheers,Christian

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Hi there,well, I won't even attempt to match the beauty of Luis' presentation ;-)However, with the recent release of the "finished" version of SRTM data the task for auto-creating islands and (if desired) their shorelines outside of North America has become a lot easier.While the SRTM data still have lots of void areas in them the processing team did a pretty good job in adding coastline data to the original SRTM data and also adding large lakes as flattened surfaces.I believe Autoasm can do similar things but I'm more familiar with Slartibartfast - http://www.jimkeir.co.uk/FlightSim/Autogen/index.html - and it makes this stuff almost too easy ;-)1. Grab the area of interest from the USGS website - http://seamless.usgs.gov/ - making sure that you select SRTM 3arcsec in either geotiff or BIL format as data source/format2. Use the zip's information to set up the geographic parameters for the Slarti inf file (how is explained in the excellent manual)3. Run Slarti to create the SRTM base mesh (with holes interpolated via a very good algorithm, much better than SRTM2BGL or MicroDEM), the water LWM files and shorelines, all in one operation. In addition, you can generate an elevation-dependent landclass file, which makes a great base for more detailed landclass work.I recently did all of Patagonia in this manner. I would have uploaded it except that adding lakes (and there are plenty in Patagonia) is a much more tedious task. One of these days...As for Luis' example of St. Thomas, below are Global Mapper preview screenshots of the SRTM 3-arcsec and 1-arcsec data (the latter are available because the Virgin Islands are US territory). And this is the direct link for those data (if it works like that, not sure): http://extract.cr.usgs.gov/Website/distreq...SM902HZ,SM302HZCheers, Holgerhttp://forums.avsim.net/user_files/128604.jpghttp://forums.avsim.net/user_files/128605.jpg

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There are some maps done from public domain source data, you can append to Sbuilder (I do not know them): http://rwsmaps.griffel.se/ very easy (give the credit to the author, when you use it)A good point Holger:What is the easier approach in FS?To make the LWM from DEM or to use LWM (vectors) for an existing DEM? (for an inexpensive approach, and a bigger coverage)And the VTP data?Horst

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Many thanks for this info, Holger. I had not checked on the SRTM corrections in the last few months, so this is news to me.I shall take a look right away. After all, I have done the islands already. And done them again. And again. So, I might as well try it all over again.The only problem with Jim's Slarty had always been the lousy quality of SRTM data, and hopefully this will make his program come into its own.Here are the images of St. John, the default first:http://forums.avsim.net/user_files/128631.gifAnd the modified Water Masks:http://forums.avsim.net/user_files/128632.gifQuite a difference! Of course, it still needs land class, water class, beaches, reefs, roads, lagoons, salt pans, golf courses, appropriate houses and vegetation, landmarks, airport buildings, ai aircraft, boats everywhere... It never ends!Best regards.Luis

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A short question for you, Holger. I had already in the past attempted to use Slarti to create Water Masks from a DEM. Unfortunately, large coastal areas that were at sea level were converted to water, requiring either much manual correction, or the creation of a Slarti "water mask" so that it could distinguish between water and land. In the end, it was shorter and more direct to just draw the Water Masks in Ground2K4.In addition, as you can see in the above example, the altitude mesh by itself would result in a simplified coast, whereas the real island is more complex and has more detail.Just out of curiosity, have you checked your Patagonic project against a good map, in order to see how well the Slarti results correlate to the real thing?Best regards.Luis

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Hi Luis,nope, I didn't have any detailed maps of Patagonia but, for that area, tracing by hand thousands of miles of shoreline isn't an option anyway.Those two preview screenshots of the SRTM data show the water mask (i.e., 0-m value) already contained in the new "finished" version. Slarti will trace the edges of the blue areas to build the LWM. As far as I can tell from comparing your LWM model to the SRTM screenshots, the SRTM blue water data shows the same amount of detail as your shorelines. You're right that one has to keep an eye out for low-lying areas. However, Slarti will limit itself to tracing only the 0-m level. Thus, only coastal areas at exactly 0m would be delimited as water bodies. I've seen this happen at river inlets but it's easy enough to fix: either manually edit the source LWM data, place a LWM-land poly over the offending area, or load the compiled bgl into SBuilder and remove those sections (the latter requires a registered version of SBuilder, I believe).For the shoreline detail I would probably use SBuilder because it's easy to append Slarti's VTP (or have SBuilder create a shoreline from the appended LWM) and then cut the lines to edit or remove sections.Cheers, Holger

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Hi,I did this some time ago with slarti. Reading the Slarti pdf I,m sure I used Landsat level 4 images to create a water map with slarti and edited it with sbuilder.Reading back through the slarti PDF it works because of the way water reflects on the level 4 images, the results were very good.David

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Hello,There is an automatic joining polygon function in Sbuilder!So it is easy to make a line from a polygon (appended mp or bgl).I did not play enough with the

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Thanks for the comments, guys. And so, I still wonder how those JPL guys got accurate coastlines for the world that let them set all water to 0 m.Do they have access to such magical source data, and if so, where is it and how can I get some?If not, are they using false-color images to map water areas and then using that to reduce the DEM water to 0 m.?Obviously, they are not using normally-available sources of coastline data, or it would not fit with the DEM, same problem as for us.But, forgive me for insisting, that SRTM image does not reflect all the detail of the real coasts, and while most people would not notice a difference, it would give a different result from an accurate topographical map. And, this does not even take into account the quite common problem of land at sea level, as I mentioned.I do not mean to knock this newest version of SRTM at all, and shall in fact welcome the cleaner data, but questions do still arise. Probably there is an information page on the seamless web site that offers a clearer explanation on the methods used.Best regards.Luis

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