Sign in to follow this  
Guest cwright

Non-flattened land?

Recommended Posts

Hi everyone, I'm experimenting with a new method with AutoAsm. I define a lake as a water polygon in the usual way. If there is an island the polygon is defined as land and so on. The island polygon will always appear later than the water polygon in the ASM file. This works fine. If I set the island to a different elevation then that works fine. However, by definition the island is flat, which is extremely boring. The obvious solution is to define the island as -9999. It seems that -9999 works for land polygons as well as water polygons. However, there is a problem. If both the water and island is defined as -9999 it works fine, with both the water and island 'clinging' to the default terrain mesh. But if I define the water as flattened (the normal case) and the island as -9999, then the island remains flat and at the same elevation as the water. It does not 'cling' to the default terrain mesh. I suspect that from the point of view of the island, the terrain that it 'clings' to is the water polygon and not the default terrain mesh. I've tried changing the layer numbers to no avail. So my question is this: if I add an island polygon over a flattened water polygon and define it as land, is there a way to make it 'cling'to the background terrain mesh? Many thanks. Best regards, Chris

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

Hi Chris,great to hear you're continuing to develop AutoASM!I've tried different things for the lake-with-island problem and the only solution I came up with is to "exclude" the island, that is, include it in the lake polygon itself (see screenshot below). If the "land bridge" to the island is very narrow then it won't be visible in FS. The drawback with this method is that you can't use the "polygon with shoreline" polygon type in Ground2K4; if one wants to have a shoreline it would have to be drawn separately. Not sure if that would be an issue with AutoASM, though this entire approach might be difficult to automate.Cheers, Holgerhttp://forums.avsim.net/user_files/71545.jpg

Share this post


Link to post
Share on other sites

Hello Chris,I think that in order to get a "meshy" island on a lake you need to remove the water under the island.You could make the flatten water polygon starting at, for example, outside point 1, going to inside point 1, than anticlockwise until 1 (inside) then 1 (outside) and finally all the rest of outside points in clockwise order. The order would be:1 1 6 5 4 3 2 1 1 2 3 4 5 6 7 8The problem would be to chose the first pair of 2 points. The segment joining the 2 first points (out 1 and in 1 in the example) should not cross any other segment.Regards, Luishttp://forums.avsim.net/user_files/71547.jpg

Share this post


Link to post
Share on other sites

>Hi Chris,>>great to hear you're continuing to develop AutoASM!>Hello, Holger, I've been working hard on AutoAsm since the last release just before Christmas. In fact I think I've made more changes and improvements in the last three months than in all of last year. Two users have been using it extensively to import TerraScene bitmaps. Their feedback has contributed greatly to the program's development. Many thanks, guys. Thank you very much for the suggestion. It works by basically defining an island as the absence of water, so the island appears as land and has the background terrain mesh applied to it. This is essentially how AutoAsm currently works. I'll try to explain briefly. The program scans a bitmap and when it finds a valid polygon it traces along it and enters the coordinates into the program arrays. Therefore polygon points are processed in the same order as they were traced in. By default polygons are traced in the clockwise direction. The geometrical calculations then convert the polygon into a lake. Originally I hadn't even considered islands, it was pretty neat just to be able to create lakes automatically. But eventually I started to look at the problem of islands. The solution was amazingly simple. All I had to do was trace islands in the counter-clockwise direction. The existing geometrical calculations automatically handled islands. It works because, if the data flow goes counter-clockwise, it 'projects' water outwards into the surrounding water (a lake 'projects' water into the polygon). This year I added automatic detection of islands so now the solution for islands (and lakes inside islands etc) is completely automatic - all the user has to do is enable the 'islands' option. So why do I need an alternative method? In most cases it works fine, but if lakes have different elevations and they have islands then, depending on the geometry, it can fail. The second method would solve that problem completely and it's also a nice, clean method (i.e. to first fill a lake completely with water and then to paint any islands over it and define them as land). After several days it's working perfectly - except for the flat islands! If there's no way to make the islands cling to the background mesh then I'll probably have to abandon it. I'll go back to the original method and try to fix the elevation problem. Once again, thank you very much for the suggestion. Best regards, Chris

Share this post


Link to post
Share on other sites

Luis, thank you very much for the suggestion. Like Holger's, I think it relies on defining an island as the absence of water, which would then allow it to cling to the background mesh. As I said in my reply to Holger, the current method in AutoAsm is also to define islands as the absence of water. It works well but there is a problem that the second method would have solved - unfortunately it results in flat islands! If islands placed over water cannot cling to the background mesh then I'll have to return to the original method and try to fix the original problem (it occurs when lakes have differnet elevations and they also have islands). Actually, a solution for that has occurred to me.... Once again, thank you very much for the suggestion. Best regards, Chris

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this