I assembled these findings after looking at the data files for a bit, certainly advancing my hex editor skills a fair bit.

Interstate 76 has a variety of different file types. A large chunk are geometry & textures, there’s a few text files, some sound files and some more specific data files. One of the specific files I looked into recently were the GDF files. While it’s a rough guess, I’m guessing it stands for ‘Gun Data File’ or some sort, as they’re specific to the weapons that vehicles have.

An asterisk before the offset indicates this extra data only appears in the updated version of the game which has had some small changes to the data files.

GDFC block

Offset	Type	Length	Description	Value (in glandmin.gdf)
0	String	16	Weapon name	Landmines
16	Int32	4		6
20	Int32	4		3
24	Float	4		160.0
28	Float	4		100.0
32	Float	4		70.0
36	?	8
44	Int32	4		240
48	Int32	4	Fireproofing	200
52	Float	4		60.0
56	String	13		drp05
69	?	9
78	Float	4	Firing Rate	1.0
82	Int32	4	Fire Amount	1
86	Float	4		1.0
90	Float	4		2.101948E-44
94	Int32	4	Ammo Count	25
98	Float	4		0.7
102	String	13	Firing sprite	null
115	String	13	Sound Filename	mines1.wav
*128	Int32	4		1
*132	String	16	Enabled Sprite	3landmines_on
*148	String	16	Disabled Sprite	3landmines_off

GPOF block - 192 bytes

Offset	Type	Length	Description	Value (in glandmin.gdf)
0	?	192

GGEO block - 4 bytes if no geometry, else 2404 bytes)

❗️❗️ This is the same data layout as the SDF file - you can re-use the SdfPart class. ❗️❗️

Offset	Type	Length	Description	Value (in glandmin.gdf)
0	Int32	4	Number of parts	0

ORDF block - 133 bytes (137 in GoG version)

Offset	Type	Length	Description	Value (in glandmin.gdf)
0	?	16
16	String	13		null
29	String	13		null
42	String	13		null
55	String	13		xmine1.xdf
68	String	12		xemt1.wav
80	Byte	1		132
81	String	12		xmine1.xdf
93	Byte	1		130
94	String	13		null
107	String	13		xmine1.xdf
120	String	12		null
132	Byte	1		130
*133	?	4

OGEO - 104 bytes

Offset	Type	Length	Description	Value (in glandmin.gdf)
0	Int32	4		1
4	String	10		MLNDMINE
14	?	46
60	String	12		WORLD
72	?	32

After doing some testing with a hardcoded vpp01.vcf for now (just to try and recreate a one-to-one match with the training mission for reference purposes.) I’ve found another slight obstacle.

It appears that there is a bit of complexity to the GGEO table..

There are 24 part slots, that are 100 bytes each. Using gmlight.gdf as a reference we can get a bit of information:

• The ‘g’ in the file name appears to refer to ‘gun’ as opposed to ‘t’ (turret).

The hardpoints on the piranha are setup like so:

Hardpoint (HLOC) Index	Name	Description	Unknown 1	Unknown 2
0	PP1_GDB1	Back Dropper Hardpoint 1	2	4
1	PP1_GIB1	Back Hardpoint 1	2	5
2	PP1_GPF1	Top Hardpoint 1	1	1
3	PP1_GPF2	Top Hardpoint 2	1	1

We can see from the hardpoint’s name, e.g. PP1_GDB1:

• The template is [car unique short name]_G[weapon type][position][index]
• Weapon values can be ‘D’ for dropper, ‘I’ for inside and ‘P’ for.. uh.. top.. I guess.
• Position values can be ‘B’ for back, ‘S’ for side and ‘F’ for front.

The weapons in the VCF are setup like so:

Hardpoint (HLOC) Index	Name	Description
0	goilslck.gdf	Oilslick
1	gmlight.gdf	30 Cal
2	gmlight.gdf	30 Cal
3	gdumb.gdf	Firerite Rocket

Diving deeper into gmlight.gdf we get these geometry names for the 24 slots in GGEO:

GGEO Index	Name	Parent	Description
0	GMLP11GN	WORLD	Top, LOD level 0
1	NULL	NULL
2	GMLP21GN	WORLD	Top, LOD level 1
3	NULL	NULL
4	GMLP31GN	WORLD	Top, LOD level 2
5	NULL	NULL
6	GMLS11GN	WORLD	Side, LOD level 0
7	NULL	NULL
8	GMLS21GN	WORLD	Side, LOD level 1
9	NULL	NULL
10	GMLS31GN	WORLD	Side, LOD level 2
11	NULL	NULL
12	GMLT11TU	WORLD	Turret base, LOD level 0
13	GMLT11GN	GMLT11TU	Turret gun, LOD level 0
14	GMLT21TU	WORLD	Turret base, LOD level 1
15	GMLT21GN	GMLT21TU	Turret gun, LOD level 1
16	GMLT31TU	WORLD	Turret base, LOD level 2
17	GMLT31GN	GMLT31TU	Turret gun, LOD level 2
18	GMLI11MZ	WORLD	Inside, LOD level 0
19	NULL	NULL
20	GMLI21MZ	WORLD	Inside, LOD level 1
21	NULL	NULL
22	NULL	NULL
23	NULL	NULL

Note there is some more data in each slot but some of it’s not relevant, or figured out.

We can see from the filename that it has a similar layout to the weapon hardpoints.

[3 letter weapon name][weapon type][LOD level][Part number][Unknown]

• Weapon type is either ‘P’ for top, ‘T’ for turret, ‘S’ for side or ‘I’ for inside.
• LOD range appears to be ‘1’ (highest detail), ‘2’, and ‘3’ (although inside weapons only have 2 LOD levels.)
• Presumably part number can go beyond ‘1’ but I’ve not seen any weapons with anything other than 1 so far.
• There’s also a suffix of ‘GN’ for gun, ‘TU’ for turret and ‘MZ’ for.. something mysterious. I don’t know why these exist as they’re already determined by the weapon type.

Yep, ‘unknown 2’ is the weapon mesh index. Unfortunately there doesn’t appear to be something similar in the GDF file so I’m still using the 3rd index in the label. The good news is the label is always 8 characters long so it’s not likely this will break.

For now, some eye candy - The drone training vehicle correctly using the “inside” mesh (really just a circle) for the front weapons and the “side” mesh for the side weapon.