[RESOLVED] hi im having trouble converting frrom 2d screen coordinates to local coordinates

[flyhigh]

hi im not sure where to put this.
these are my local coordinates of 1 of my triangle points

     With ONEobject
     .LocalCoord(0).X = -1
     .LocalCoord(0).Y = -0.5
     .LocalCoord(0).z = 2.5
     End With

and this is how project the 3d coordinats on to a 2d plane

Private Sub LocaltoScreen()
  
  Dim lngIncr   As Long         'counter
  Dim tempcoord As Point3d      'buffer to hold temporary converted coordinates
  
    With ONEobject
        For lngIncr = 0 To .NumVertices
            'converts local coordinates into world ones relative to the supplied Canvas
            tempcoord.X = .rotatedLocalCoord(lngIncr).X + .CenterofWorld.X
            tempcoord.Y = .rotatedLocalCoord(lngIncr).Y + .CenterofWorld.Y
            tempcoord.z = .rotatedLocalCoord(lngIncr).z + .CenterofWorld.z
            'now we project the 3d coordinats on to a 2d plane with perspective
            .ScreenCoord(lngIncr).X = (tempcoord.X * HPC / tempcoord.z) + HCW
            .ScreenCoord(lngIncr).Y = (-tempcoord.Y * VPC * ASPECT_COMP / tempcoord.z) + HCH
        Next '  LNGINCR
    End With 'ONEobject
 
End Sub

using my mouse i will add three points to the screen ,how do i turn these screen coordinats
into local coordinats or is there a better way other than local coordinats?
thanks

[Schmidt]

That's not a true reversible action, mapping a point from 2D-Screen-Coords-Space back exactly into the 3D-World.
At least not "with a single click" (if there's no sufficient side-condition defined).

This first "single click" in your Screen-View to position something new in 3D-Space, can only make
"reasonable guesses" (e.g. finding the next nearest already defined objects or points in the surroundings
of the area you clicked - and then calculate a "near average" for x, y and z of the surrounding nearest
objects or points - and then derive the "depth-info" for your new point from that average.

To "elevate" the placement of your new point to an exact operation (so far, you have only a "good guess"
about the correct depth - you could rotate the current view e.g. about 90Degree horizontally - and then
correct the point you've just set.

Or instead of such a manually accomplished (per extra-click) "follow-up-rotation", you could additionally
offer a second, always visible view onto the scene (kinda like a Stereo-View) - and then e.g. make your
click in one view - and correct it in the other (or vice versa).

Olaf

[Niya]

You could try PMing Jacob Roman to this thread. He should have experience dealing with this sort of thing since he writes a lot of game related stuff.

[flyhigh]

hey
im making a 3d Model Maker if it works out.
schmidt your saying make different views then?

[Schmidt]

hey
im making a 3d Model Maker if it works out.
schmidt your saying make different views then?

Only if you need that in a fashion, which requires to position single points accurately.
There's just no exact placement of a 3D-Point possible from a 2D-ScreenView-Coordinate -
not enough info "to hang onto".

If it's only thought for a Designer (beaming new, complete Objects into the 3D-Space),
then one approach could be, to place the center of the new Object exactly at the
Center of your World - or at whatever "central 3D-place" makes sense at that point -
and *that*could be accomplished with a simple MouseAction - you could then move
the Object from this central WorldPoint the User always expects it to shine up, to
different places in the World - along with Rotations around the internal Center,
(using the local-Coord-System of your newly placed 3D-Object) you should be able
to place it exactly where it needs to end-up in the scene.

So, what I mean is a bit similar to the VB6-IDE-behaviour, when you DoubleClick
at a Control-Icon in the Selector-Panel.
In this case you also don't give a specific position for the Control on the Destination -
the new Control will just end up centered on the Form - a place you expect it to shine
up - then you move it from there (e.g. using <Ctrl>+<ArrayKeys>).

Just trying to make the principle more clear, which you could follow in your UI.

Olaf

[flyhigh]

thank yall