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Sloping AB polys do not slope evenly

K

klem

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unitedkingdom
I have created a sloping AB Poly on the north side of my airport. It is approx 1500m wide by 500m deep and rises to a suitable road line running E-W, north of the airport. It is 14m at the south edge and 23 m at the north edge. I set the basic poly elevation at 23m.

I have set Vertexes for individual elevations and these appear to work ok but several metres north of the southern edge it 'humps' up to 23m. I tried controlling it with a set of 1m interval Vertexes up the west side and that appears to work up that edge but the hump is still present further in.

What should I do to make it rise evenly across the whole width of the poly?

Thanks

klem
 
You need to blend it to the surrounding mesh. Here is one of mine containing two sloped paths. Note how they are surrounded by triangles to connect to the mesh:



George
 
Thanks George,

I just know I am going to regret asking this but I assume the mesh can be shown in ADE? I have looked around the various options/commands etc but I cannot see a 'show mesh' control.

I assume from your picture that I just align appropriate parts of the poly edges with the nearest mesh lines and it will automatically give me a smooth slope?

klem
 
klem said:
Thanks George,

I just know I am going to regret asking this but I assume the mesh can be shown in ADE? I have looked around the various options/commands etc but I cannot see a 'show mesh' control.

I assume from your picture that I just align appropriate parts of the poly edges with the nearest mesh lines and it will automatically give me a smooth slope?

klem
Click to expand...

You will regret asking it - no you cannot see mesh in ADE. George is using TmfViewer to show the underlying mesh. This comes with the SDK and is in the Terrain folder
 
klem said:
I assume from your picture that I just align appropriate parts of the poly edges with the nearest mesh lines and it will automatically give me a smooth slope?
Click to expand...
I'm afraid it is not that easy :D

You cannot see the mesh lines in FSX let alone ADE. What I do is add vertex points at recognisable boundaries such as edges of fields, roads etc. The heights of these vertices can be obtained either from the ADE display or, more conveniently, from TCalcX. If you need to connect to your your slope, you need to interpolate individual heights between the top and bottom of the slope.



George
 
Last edited:
ok Gorge, I thought that was where I was going but it didn't seem to work.

The large polys N and S of the airport boundary are set up with the appropriate elevations along their N and S edges but I get that 'hump'. (I am already using recognisable features as poly limits).

Should I have set the basic poly elevation to 0 instead of somewhere in between the two elevations?

Should I use smaller polys so that the 'humps' don't develop?

klem
 

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Hi Klem,

It's difficult to tell from your screenshot exactly where the sloped polygons are.

I find it is necessary to use triangles for sloped polygons (unless they are between two known heights) since more than three vertices will produce a twisted plane and the outer edges may cause humps and/or hollows.

George
 
Bless you,George

I've had trouble with sloped polys all along. It never occured to me that the triangles I made worked fine while polygons did not. I just redid an area with triangles and all is well. Oh, for a brain!

Bob
 
Triangles

Before I try, it and confuse myself, can all three points of the triangle be a different elevation? I assume it does not have to be equilateral? And, is the shape of any consequence?

Dick near Pittsburgh
 
Any shape triangle seems to work, and all three vertexes can be different altitudes(that is the point, after all). Can someone tell us why triangles work and quads and up do not?

Bob
 
bobbyjack said:
Can someone tell us why triangles work and quads and up do not?
Click to expand...
A unique plane can be constructed through any three points.

Consider a quadrilateral with opposite corners at the same height and the other pair of opposite corners at a different height. What would you expect the height to be at the point where the diagonals cross?

Of course you can use multi-sided polygons if all vertices are at the same height.

George
 
Last edited:
Thanks, George

Consider a quadrilateral with opposite corners at the same height and the other pair of opposite corners at a different height. What would you expect the height to be at the point where the diagonals cross?
Click to expand...

OK, after taking some asprin I understand this. I was a music major in college, so some these 3d things take awhile for me to catch. Besides, college was a long time ago.

Bob
 
Well, I got there, triangles were the answer :)

Tip for readers: I took a top down shot and wrote terrain elevation points onto it in Paint using Slew and TcalcX in FSX, then added the image to ADE, slid it under my airport and worked the triangles from the main ABP edges out to the mapped points. Easier than jumping back and forth.

Many thanks for your help guys (and apologies to George for calling him Gorge!)

I just have one more question. My Airport has crossed runways surrounded by a taxi-way, laid over the Horizon Photographic scenery.

I have laid Land Class polys (Grass) in the quadrants between runways and taxiway (over the APB flatten) but they do not appear, the photo detail is still showing.

What am I doing wrong?

klem
 
klem said:
What am I doing wrong?
Click to expand...
You are not doing anything wrong, landclass affects only the default textures, photographic textures are already 'correct'. Just remove your landclass polygon.

George
 
OK George, thanks.

I was trying to 'rebuild' an airport that closed in 1975, since when some buildings have been erected on it and i was trying to blank them out. I suppose I could look for objects like grass runways to do that... hmmmmm....

Anyway, thanks again.

klem
 
You could use grass aprons but I think they look naff. Better to make a textured plane in GMax. But don't ask me how ;)

George
 
Golf-HotelDelta said:
You are not doing anything wrong, landclass affects only the default textures, photographic textures are already 'correct'. Just remove your landclass polygon.
George
Click to expand...

If you leave the landclass poly in, although it doesn't show over the photo scenery, it will show for anyone without it (an important consideration if you're thinking of distributing your airport once its finished).
 
Thanks for that Tim, a good point.

In fact I am going to use grass Aprons as George suggested. They don't look too good but they're better than the rows of greenhouses on the photo scenery. Just wish I could change their colour or texture.

klem
 
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