About VTP lines and hooks

General discussion about Scenery Design. Questions about SBuilder for Flight Simulator FS2004.
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Luis Sa
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Joined: Sun May 18, 2003 11:17 am
Location: Portugal

About VTP lines and hooks

Post by Luis Sa » Sat Oct 02, 2004 11:52 pm


Here is an explanation about VTP hooks.

If, in the Australia folder, you open the file HL986450.BGL with the recent TmfViewer (the one dated 2004) and go to:


you can get the following picture. Look to the 3 views of the same line junction. They use different settings of the viewer.


On the top only the points are drawn. You will see the hooks. On the centre I asked TmfViewer to draw wide lines as polygons. On the bottom I asked TmfViewer to fill polygons.

You see that there is a starting hook and a ending hook. Points 1 and 2 and points N-1 and N are used to make the side of a triangle. Note that VTP lines are in fact polygons. Here is what I wrote recently on the AVSIM Scenery forum:

I think that any VTP line should have at least 4 points. Points 1 and 2 will generate the "true first" point and points N-1 and N will generate the "true last point". Based on TMFViewer display I assume that each midle point is internally translated to 2 points. I am using VTP Lines in SBuilder as follows:

1) I do not allow the width of the line to be greater than 255
2) I start the line with 2 points. These 2 points are perpendicular to the first line segment and their distance is the starting width of the line. The "mean position" of these 2 points is the position of the starting point of the source line.
3) I end lines with 2 points which are perpendicular to the last segment of the line. Again their distance is the width of the last point in the source line. The "mean position" of these 2 points is the position of the ending point of the source line.
4) I created an option in the VTP file import which I call "Remove Hooks". If this option (a check box) is set, Sbuilder imports 4 points lines as 2 points. If I do not set the option, Sbuilder import the points as if they all are different (as for example you see them in LWMViewer).

I suggest that you allways set this box.

Regards, Luis

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