Hi Ken:
My point is, output from GMAX (or Sketchup) used to make a G-Poly , is best optimized via MCX for each FS2Kx version.
Notice in MCX Ground Polygon Wizard (aka "GPW") GUI, at least (5) FS2Kx versions are shown in that MCX Ground Polygon
configuration dialog box.
Other G-Poly tweaks may also be needed that are not shown in that dialog box, and may not be explained in the MCX PDF Manual.
Instead, they may require extensive review of older FS forum threads
The June 9, 2025 MCX Manual section on the G-Poly Wizard follows:
7.2 Ground polygon wizard
If you use normal scenery objects for your custom ground polygons they will typically flicker,
because the different textures have not been layered correctly. And for FSX and Prepar3D you
will also run into the issue of floating polygons due to the curve of the earth. The ground polygon
wizard, see Figure 7.2, is a tool that will help you to create a ground polygon BGL file without
these issues.
Figure 7.2: Ground polygon wizard
When using the wizard you will fill in all details of the window, the steps are:
1. Select the object that contains the ground polygons using the ... button. The check-boxes to
Project flat polygons and Filter out non-ground polygons affect how your object is
loaded from the specified file. By default both these options are enabled and that will give
the best results in general.
Projecting polygons on the ground means that all polygons for which the dot product of the
normal vector and the upwards normal is above the specified threshold value will be projected
onto ground level. This lowers them to the ground. So for example the roof of a house will
then become a ground plane.
Filtering out non ground polygons means that all polygons whose Z coordinate values are
not zero will be removed from the object.
2. Select the output BGL file for the ground polygon using the ... button.
3. After selecting the object to convert, the list of materials in the object will be filled. In this
grid you see the material name, layer, viability, night texture and seasonal texture status.
You can alter any of these columns to specify how the ground polygon should be created.
For FS2004 and FSX the layer values are positive and typically an increment of 4 is used
between the layers The higher the layer number the more priority the texture has. For
Prepar3D the layer values are negative, the more negative the number the higher the priority
of the texture is. The wizard will make sure that the numbering convention of the selected
output simulator is used, so if you enter positive layers, but export to Prepar3D that will be
fixed.
The visibility value indicates at which distance the polygon should become visible. This is
only supported for FS2004 and FSX output, else this column will be disabled.
The night texture (_LM) checkbox indicates if this material has a night texture assigned. You
will have to ensure yourself that the corresponding texture file also exists.
The seasonal texture checkbox indicates if this material has seasonal textures assigned. This
is only supported for FS2004, FSX and Prepar3D v4 output, else this column is disabled.
4. With the Convert textures checkbox you can indicate if the textures of the object should
be converted as well. If enabled, the output folder is specified in the textbox below (you can
use the ... button to select the folder). With the Overwrite existing textures checkbox
you can indicate if existing textures should be overwritten during the conversion.
5. Specify the position where the ground polygons should be placed. See section 13.1 for more
information about how to specify the position.
6. In the options section select for which FS version you want to create ground polygons. Certain
options might be disabled based on the version you select.
7. The Slice polygons checkbox determines if polygons should be sliced into pieces of 100
meter. To be able to follow the curve of the earth correctly your polygons need to be small
enough, so when you disable this option make sure you slice them in your modelling tool.
8. The Group polygons checkbox determines if polygons are grouped together. These grouped
polygons than become one object or reference point in the output BGL file. In general
grouping the polygons together for a given area improves the performance in the simulator.
With the textbox you can specify the size of the grid that is used for grouping.
9. The Optimize reference point checkbox determines if the reference point is placed optimally
in the center of the object. When grouping polygons this option is always enabled.
10. The Prevent autogen exclusion checkbox determines if your ground polygons should
prevent autogen object suppression or not. For FS2004 and FSX output a hack is used to
prevent the suppression, for other versions the BGLComp placement flag is used.
11. The DX10 compatibility checkbox determines if the FSX output is written in such a way
that it also works in DX10 mode of FSX. This however disables the use of night textures.
12. With the All textures _LM checkbox you can quickly enable or disable the night texture
status on all materials.
13. With the All textures seas checkbox you can quickly enable or disable the seasonal texture
status on all materials.
14. With the Define seasons button you open the editor to define the seasons, see section 6.11
for more details.
15. Once all settings are set, you can use the Convert button to start the creation of the ground
polygon BGL file.
With the Save settings button you can save all the settings that you made for the ground polygons
to a file, so that you can reuse them later when you want to convert the same object again. With
the Load settings button you can load them back in again.
GaryGB
