MCM1 National Track File Formats

Version 1.0 (Beta) - 7/9/26

This document describes National-style track-side files used by Motocross Madness 1:

• .asc - 3ds Max / Charityware grid mesh terrain source

• .dat - binary National track-path spline

• .scn - scene descriptor, lighting, sky cube, and gate scale

• .ter - National MakeTerr terrain compile input

• .trn - compiled National terrain

These National formats are different from the Supercross / TrackEdit formats described in docs/MCM1_TRACK_FILE_FORMATS.md. In particular, National .dat files are spline paths, while Supercross .dat files are fixed 16 x 16 per-cell navigation fields.

The formats below are intended for programmers implementing readers, writers, validators, or conversion tools.

Other links:

• Coordinate Systems

• National Track File Set

• General Rules

• Relationship to MakeTerr

• Tools

Format Map

Use these links to jump directly to the file format you need:

General Rules

All binary integer and floating-point fields described here are little-endian.

The .scn and .ter files are INI-like text:

• Lines are normally CRLF terminated.

• Section names are written as [SectionName].

• Key/value lines use Key=Value.

• Blank lines and semicolon comments are common and should be ignored by .scn and .ter readers.

The .asc file is a text mesh export. Height readers normally need only the vertex lines, while exporters commonly write both vertex and face lists.

The .dat and .trn files are binary.

Coordinate Systems

The National world is a 5 x 5 terrain centered in Direct3D space. The following constants are used by common National tooling:

SIZE = 10
S = SIZE / 256
WO = 1920

WO is the Direct3D world-center offset for National tracks:

xxxxxxxxxx
WO = TotalTargetWidth * 1.5
WO = 1280 * 1.5
WO = 1920

Authoring tools often store path points in scene coordinates as x and z. National .dat and .scn files use MCM / Direct3D coordinates.

Editor path point to .dat Direct3D coordinate:

​x
MAX_X = editor_x / S
MAX_Y = -editor_z / S

D3D_X = MAX_X * 3 + WO
D3D_Y = 0
D3D_Z = MAX_Y * 3 + WO

Inverse conversion used by the .dat importer:

xxxxxxxxxx
MAX_X = (D3D_X - WO) / 3
MAX_Y = (D3D_Z - WO) / 3

editor_x = MAX_X * S
editor_z = -MAX_Y * S

For .scn sun lights, 3ds Max-style sun coordinates can be used as an intermediate:

xxxxxxxxxx
Max X = R * cos(elevation) * cos(azimuth)
Max Y = -R * cos(elevation) * sin(azimuth)
Max Z = R * sin(elevation)

Then it writes the Direct3D light position as:

xxxxxxxxxx
SCN Position = MaxX * 3 + WO, MaxZ * 3, MaxY * 3 + WO

A reader can use DefaultStartPosition as the source for WO when it is present, then apply the inverse:

xxxxxxxxxx
Max X = (D3D_X - WO) / 3
Max Y = (D3D_Z - WO) / 3
Max Z = D3D_Y / 3

.ASC Format - National Height Mesh Source

FORMAT BANNER: .ASC

3ds Max / Charityware Grid mesh export used as the National terrain height source. Example: tracks/national_test.asc.

National authoring workflows use .asc files as real-height terrain sources. A square grid can be imported from an existing .asc, edited, and exported as an .asc that MakeTerr can consume through a .ter file.

Readers should expect a text mesh with a vertex list. Exporters commonly write both a vertex list and a face list.

Generated Structure

xxxxxxxxxx

Named Object: "MyGrid"
Tri-mesh, Vertices: <N*N>     Faces: <(N-1)*(N-1)*2>
Vertex list:
Vertex 0: X: -128.000000     Y: -128.000000     Z: <height>
Vertex 1: X: -127.000000     Y: -128.000000     Z: <height>
...
Face list:
Face 0:    A:<i10> B:<i00> C:<i11> AB:1 BC:0 CA:1
Smoothing: 2
Face 1:    A:<i01> B:<i11> C:<i00> AB:1 BC:0 CA:1
Smoothing: 2
...

The blank first line appears in common generated files.

Grid Size

N is the terrain source resolution. National .trn compilers ultimately use a 257 x 257 center height grid.

ASC readers should accept any square grid with at least 4 vertices:

xxxxxxxxxx
vertex_count >= 4
N = round(sqrt(vertex_count))
require N * N == vertex_count

Vertex Coordinates

The writer emits vertices in row-major order:

xxxxxxxxxx
for r in 0..N-1:
  Y = -128 + r * (256 / (N - 1))
  for c in 0..N-1:
    X = -128 + c * (256 / (N - 1))
    Z = terrain height

Vertex index:

xxxxxxxxxx
vertex_index = r * N + c

Readers can identify vertex lines with this pattern:

xxxxxxxxxx
Vertex <number>: X: <float>     Y: <float>     Z: <float>

Only the numeric X, Y, and Z values are used. The vertex number is not used to reorder vertices; order in the file is the source of truth.

Height Export

For a raster-derived heightmap, an exporter can convert authoring units back to ASC / Max units with:

xxxxxxxxxx
S = SIZE / 256
Z = (baseLum * heightScale + sculptDelta) / S

For an imported .asc, an exporter can preserve imported scale metadata:

xxxxxxxxxx
Z = (ascHeights + ascEdge + sculptDelta) / ascScale

Some importers set ascEdge = 0, keeping imported heights exactly apart from uniform scale into authoring units.

Row Orientation

The .asc file lists rows from Y = -128 to Y = 128. Authoring tools may flip rows north/south into their internal height arrays:

xxxxxxxxxx
editor_index = (N - 1 - r) * N + c
editor_height = asc_Z * scale

On export, the row order should be flipped back consistently if the internal height array uses the opposite north/south orientation.

Import Scale

When importing, a reader can compute one uniform scale from the X span:

xxxxxxxxxx
horiz = max(1e-6, x_max - x_min)
scale = SIZE / horiz

That same scale is applied to X/Y/Z semantics by storing:

xxxxxxxxxx
editor_height = asc_Z * scale

Importers may retain X/Y bounds as metadata. Common exporters emit the standard -128..128 grid.

Face List

ASC exporters commonly emit two triangles for each grid cell:

xxxxxxxxxx
i00 = r * N + c
i01 = r * N + c + 1
i10 = (r + 1) * N + c
i11 = (r + 1) * N + c + 1

Face A: A=i10 B=i00 C=i11 AB:1 BC:0 CA:1
Face B: A=i01 B=i11 C=i00 AB:1 BC:0 CA:1
Smoothing: 2

Terrain importers may ignore the face list and reconstruct terrain from the ordered vertex grid only.

.ASC Reader Behavior

A typical .asc terrain reader:

• extracts all Vertex ... X ... Y ... Z ... lines

• requires the vertex count to form a square grid

• computes min/max X, Y, and Z

• computes a uniform scale from the X extent

• flips rows north/south into internal terrain order, if needed

• uses the scaled Z values as source-of-truth heights

• ignores all face records

.TER Format - National MakeTerr Input

FORMAT BANNER: .TER

National MakeTerr terrain compile input. Example: tracks/national_test.ter.

The .ter file tells National MakeTerr how to assemble ASC height sources and TGA texture maps into a compiled .trn.

Header

The National 5 x 5 template writes:

xxxxxxxxxx
[ElevationData]
GridResolutionInFeet=3.0
TerrainType=NATIONAL
TotalElevationFiles=73
TotalTextureMapFiles=2
TotalTexturePlacements=1
TotalTargetWidth=1280
TotalTargetBreadth=1280
ElevationFormat=ASC
ElevationDefault=0
ElevationAtEdge=<edge elevation>
TextureFormat=8
ShareTextures=1
ShareGeometries=1
UpPropagateTextures=1
ElevationPath=.\
TextureMapPath=.\

Header Keys

GridResolutionInFeet

Often 3.0. Other values are valid. For example, 4.0 makes a 256 x 256 center section cover 1024 ft x 1024 ft instead of 768 ft x 768 ft.

Compiled National .trn files store the corresponding scale as:

xxxxxxxxxx
trn_height_scale = GridResolutionInFeet / 256
GridResolutionInFeet = trn_height_scale * 256

This value controls horizontal terrain scale. It does not change the vertical Tga2Asc.exe maxheight value.

TerrainType

Use NATIONAL for National tracks. STUNTQUARRY and BAJA are separate terrain types and use different world layouts.

TotalElevationFiles

Usually 73 for National 5 x 5 terrain.

TotalTextureMapFiles

Usually 2:

• texture.tga for the main center terrain texture

• tile.tga for the perimeter / edge tile texture

TotalTexturePlacements

Usually 1 for National 5 x 5 terrain. Only the main 1016 x 1016 texture is placed explicitly; the perimeter tile is referenced as a texture map file for MakeTerr's edge handling.

TotalTargetWidth, TotalTargetBreadth

Usually 1280 and 1280. This is the 5 x 5 National target measured in terrain grid units:

xxxxxxxxxx
5 center/perimeter cells * 256 grids = 1280

ElevationAtEdge

Elevation value at the terrain edge. Some exporters use the mean elevation around the current terrain edge; others use a manual National edge elevation value.

ElevationPath, TextureMapPath

Often local folder paths:

xxxxxxxxxx
.\

Terrain Palette

xxxxxxxxxx
[TerrainPalette]
TotalFileSets=2
NumberOfColors=256
FileSet_1=.\tile.tga
FileSet_2=.\texturea.tga

The embedded template includes historical absolute paths, but buildTerFile strips those down to local file names:

xxxxxxxxxx
FileSet_N=<anything>\<file> -> FileSet_N=.\<file>

Some exporters normalize texture names to lowercase texturea.tga, texture.tga, tilea.tga, and tile.tga.

Texture Map Files

xxxxxxxxxx
[TextureMapFile_1]
Name=texture.tga
CoverageInGrids=256
PixelsPerGrid=4

[TextureMapFile_2]
Name=tile.tga
CoverageInGrids=16
PixelsPerGrid=4

TextureMapFile_1 is the main exported terrain texture. The export bundle also includes texturea.tga, the smaller palette source named by [TerrainPalette].

TextureMapFile_2 is the National perimeter tile. The export bundle also includes tilea.tga, the smaller palette source named by [TerrainPalette].

Texture Placement

The National 5 x 5 template contains one texture placement:

xxxxxxxxxx
[TexturePlacement_1]
MapId=1
XIndex=512
YIndex=512
Transform=NONE

This places the main terrain texture over the center 256 x 256 grid area of the 1280 x 1280 target.

Elevation File Layout

The National template contains 73 elevation sections:

xxxxxxxxxx
ElevationFile_1..36   outer edge / flat quarry surround
ElevationFile_37..40  corner transition pieces
ElevationFile_41..64  side transition strips with ForceEdges
ElevationFile_65..73  3 x 3 center terrain references

All elevation sections use INI keys:

xxxxxxxxxx
[ElevationFile_N]
Width=<grid width>
Breadth=<grid breadth>
BaseX=<target grid x>
BaseY=<target grid y>
Name=<asc file>
Base=<base elevation>
VerticalMultiplier=<scale>
ForceEdges=<optional edge flags>

Outer Surround Sections

The outer surround references stock quarry ASC files that must be available next to the .ter when using external MakeTerr:

xxxxxxxxxx
quarryF.asc
quarrySW.asc
quarrySE.asc
quarryNW.asc
quarryNE.asc
quarryS.asc
quarryN.asc
quarryW.asc
quarryE.asc

Most outer sections are 128 x 128:

xxxxxxxxxx
Width=128
Breadth=128
Base=<usually 15.0>
VerticalMultiplier=1.5

Side transition strips include ForceEdges:

xxxxxxxxxx
ForceEdges=N
ForceEdges=S
ForceEdges=E
ForceEdges=W

Center Terrain Sections

The 3 x 3 center terrain sections reference the exported terrain ASC. Template files often use grid.asc as a placeholder, which should be replaced with:

xxxxxxxxxx
<baseName>.asc

The center sections are:

xxxxxxxxxx
ElevationFile_65..73

Each center section is 256 x 256 and uses ForceEdges=NSEW:

xxxxxxxxxx
[ElevationFile_69]
Width=256
Breadth=256
BaseX=512
BaseY=512
Name=<baseName>.asc
Base=<asc edge base>
VerticalMultiplier=1.0
ForceEdges=NSEW

ElevationFile_69 is the actual center 1 x 1 chunk where the track resides. Its VerticalMultiplier remains 1.0.

The surrounding eight center references reuse the same ASC with different VerticalMultiplier values from the template. These provide blended terrain around the playable center:

xxxxxxxxxx
65: BaseX=256  BaseY=256  VerticalMultiplier=-0.398999
66: BaseX=512  BaseY=256  VerticalMultiplier=0.450868
67: BaseX=768  BaseY=256  VerticalMultiplier=-0.245357
68: BaseX=256  BaseY=512  VerticalMultiplier=0.146992
69: BaseX=512  BaseY=512  VerticalMultiplier=1.0
70: BaseX=768  BaseY=512  VerticalMultiplier=0.368007
71: BaseX=256  BaseY=768  VerticalMultiplier=-0.316102
72: BaseX=512  BaseY=768  VerticalMultiplier=-0.319767
73: BaseX=768  BaseY=768  VerticalMultiplier=0.416770

Base Elevation Patching

An exporter may compute an ASC edge base:

xxxxxxxxxx
ascEdgeBase = ascMeta.edge / ascMeta.scale

If no separate edge metadata is available, this is commonly 0.00000.

For National 5 x 5 .ter output, replace the template center base value:

xxxxxxxxxx
Base=6.45742... -> Base=<ascEdgeBase>

This changes the nine center ASC references while leaving the stock outer quarry/surround base values intact.

Base, Tga2Asc maxheight, and Editable TGA Gray

Tga2Asc.exe converts a grayscale TGA to ASC heights using a maxheight argument. From the FireRoad sample:

xxxxxxxxxx
ASC_Z = gray * maxheight / 255

The sample FireRoadNatDispMap257g.tga and .asc were created with:

xxxxxxxxxx
maxheight = 25 ft

MakeTerr then compiles ASC heights into TRN raw heights using the center section Base value:

xxxxxxxxxx
raw_height = round(256 * (ASC_Z - Base) + 3840)
ASC_Z = Base + ((raw_height - 3840) / 256)

The original TGA's darkest usable gray is not stored directly in the .trn. Many combinations of TGA gray range, Tga2Asc.exe maxheight, and .ter Base can compile to the same raw TRN heights.

For extraction tools, a practical workflow is to choose an editable darkest gray target, commonly around 50..58, then solve for a matching Base and maxheight. Using a target gray of 55 on FireRoad gives:

xxxxxxxxxx
Base ~= 5.39
Tga2Asc maxheight = 25

This is close to FireRoad's known center Base=5.41 and keeps the extracted TGA out of the too-dark-to-edit range.

.TER Reader Behavior

.ter readers should treat the file as MakeTerr source data: parse the [ElevationData] header, terrain palette, texture map files, texture placements, and elevation file sections. A .ter alone is not enough to reconstruct all game-side data; referenced ASC and TGA assets are required.

.SCN Format

FORMAT BANNER: .SCN

National scene descriptor that tells MCM1 which compiled terrain file to load and configures the lighting, sky cube, and start gate scale. Example: tracks/national_test.scn.

The .scn file is INI-like text. National scene files normally use a fuller scene descriptor than the minimal Supercross form.

Generated Structure

xxxxxxxxxx
; MCM scene file
[SceneInfo]
SceneName=<track name>
LogProgress=F
DefaultStartPosition=1920.0,100.0,1920.0
DefaultStartDirection=0.0,0.0,1.0

[Environment]
TerrainFile=<baseName>.trn
CubeFile=<sky cube>
ParticleTextureMapName=particles\track02p.tga
StartGateScale=<float>

[Lights]
NumberOfLights=2

[Light1]
Type=Ambient
ColorRGB=<r>,<g>,<b>

[Light2]
Type=ObjectPoint
ColorRGB=<r>,<g>,<b>
Position=<x>,<y>,<z>
TargetPosition=0.0,0.0,0.0
PlaceLightAtInfinity=T
CastsShadows=T
EmitsLight=T
HasLensFlare=F

[Fog]
ColorRGB=130,130,190

[Sounds]
CrowdPresent=F

Keys

SceneName

Human-readable track name. Exporters commonly use either the authoring UI track name or the sanitized file base name.

DefaultStartPosition

Direct3D world start position. For National tracks the generated value is:

xxxxxxxxxx
1920.0,100.0,1920.0

Readers can use the first component as the world-center offset when converting imported light positions back to authoring controls.

DefaultStartDirection

Generated as:

xxxxxxxxxx
0.0,0.0,1.0

TerrainFile

Compiled terrain file loaded by the game:

xxxxxxxxxx
<baseName>.trn

CubeFile

Sky / horizon cube. Readers can normalize this value to a known sky-cube list when a case-insensitive match exists. Otherwise, keep the imported string.

ParticleTextureMapName

Generated as:

xxxxxxxxxx
particles\track02p.tga

StartGateScale

Floating-point start gate scale.

Light1

Ambient light. Readers can find the first [LightN] where Type=Ambient and read ColorRGB.

Light2

Sun / key light. Readers can use the first non-ambient [LightN] with a Position key, reading Position and ColorRGB.

Fog

Common generated files use this fog color:

xxxxxxxxxx
130,130,190

Sounds

Common generated files use:

xxxxxxxxxx
CrowdPresent=F

.SCN Reader Behavior

A typical .scn reader:

• parses INI sections and key/value pairs

• ignores blank lines and semicolon comments

• reads ambient color from Type=Ambient

• reads sun color and sun position from the first non-ambient light with Position

• reads DefaultStartPosition to recover the world-center offset

• reads StartGateScale

• reads CubeFile

.DAT Format - National Track-Path Spline

FORMAT BANNER: .DAT

Binary National track-path spline. Example: tracks/national_test.dat.

The National .dat file is a variable-length list of path control points. It is not the Supercross 16 x 16 navigation field.

Total Size

xxxxxxxxxx
4 + (point_count * 20) bytes

Readers should require the file size to match exactly.

Header

xxxxxxxxxx
offset  size  type   field
0x0000  4     u32    point_count

point_count must be at least 2. Readers should reject unreasonable values such as counts greater than 100000 as a sanity guard.

Point Records

After the 4-byte header, there are point_count records. Each record is 20 bytes:

xxxxxxxxxx
offset  size  type   field
+0      4     f32    D3D_X
+4      4     f32    D3D_Y
+8      4     f32    D3D_Z
+12     4     f32    width
+16     4     u32    type

D3D_X, D3D_Y, D3D_Z

Direct3D-space control point position. National path writers commonly emit D3D_Y = 0.

width

Full track/path width in Direct3D units. If an authoring tool stores each node width as a half-width, export doubles it:

xxxxxxxxxx
width = editor_half_width * 6 / S

A reader can convert the full width back to authoring half-width:

xxxxxxxxxx
editor_half_width = max(0.03, (width / 3) * S * 0.5)

type

Common writers emit:

xxxxxxxxxx
0 for the first point
2 for all later points

Readers may ignore this field beyond validating the record size.

Writer Pseudocode

xxxxxxxxxx
write_u32_le(point_count)

for i in 0..point_count-1:
  MAX_X = point[i].x / S
  MAX_Y = -point[i].z / S
  width = point[i].half_width

  write_f32_le(MAX_X * 3 + WO)
  write_f32_le(0)
  write_f32_le(MAX_Y * 3 + WO)
  write_f32_le(width * 6 / S)
  write_u32_le(i == 0 ? 0 : 2)

Reader Pseudocode

xxxxxxxxxx
point_count = read_u32_le()
require point_count >= 2
require file_size == 4 + point_count * 20

for i in 0..point_count-1:
  D3D_X = read_f32_le()
  D3D_Y = read_f32_le()
  D3D_Z = read_f32_le()
  width = read_f32_le()
  type = read_u32_le()

  MAX_X = (D3D_X - WO) / 3
  MAX_Y = (D3D_Z - WO) / 3

  point.x = MAX_X * S
  point.z = -MAX_Y * S
  point.half_width = max(0.03, (width / 3) * S * 0.5)

National spline paths are usually treated as closed loops by authoring tools.

.TRN Format - National Terrain

FORMAT BANNER: .TRN

Compiled National terrain. Example: tracks/national_test.trn.

National .trn files contain terrain patches, palette and lookup data, texture tiles, and a tail / quadtree used for culling and LOD.

Header

xxxxxxxxxx
offset  size  type     field
0x0000  4     char[4]  "TRN\0"
0x0004  4     u32      version = 2
0x0008  4     u32      texture_format = 1

When texture_format == 1, a color-mapper section follows the 12-byte header.

Color Mapper Section

xxxxxxxxxx
u32 first_color_index
u32 color_count
u32 flag

block palette
block lut_32768
block lut_65536

Common National writers emit:

xxxxxxxxxx
first_color_index = 0
color_count = quantized color count, usually 256
flag = 1

Each color-mapper block uses this framing:

xxxxxxxxxx
u32 payload_size
payload bytes

The payload may be raw or MCM LZW-compressed.

Canonical raw payload sizes:

xxxxxxxxxx
palette   = 768 bytes      256 * RGB
lut_32768 = 32768 bytes
lut_65536 = 65536 bytes

LZW Stream

LZW payloads begin with a 4-byte little-endian subheader equal to the compressed payload length. The bitstream uses these control codes:

xxxxxxxxxx
LZW_END   = 256
LZW_INC   = 257
LZW_CLR   = 258
LZW_FIRST = 259
LZW_MAX   = 0x7FFF

The initial code width is 9 bits. LZW_INC increases the code width. LZW_CLR clears the dictionary and resets the width to 9 bits. LZW_END terminates the stream.

Patch Table

After the color mapper, the parser expects a patch-list header:

xxxxxxxxxx
u32 unknown_0
u32 unknown_1
u32 patch_count
u32 patch_offsets[patch_count]

The parser then walks patch data sequentially. Each patch contains three spans:

xxxxxxxxxx
for patch in 0..patch_count-1:
  for span in 0..2:
    u32 stored_size
    u32 raw_size
    bytes payload[stored_size or raw_size]

Compression is detected per span:

xxxxxxxxxx
compressed = stored_size < raw_size

If compressed, the payload is decoded as an MCM LZW stream. If not compressed, the raw payload bytes are used directly.

Center Terrain Patches

Known National terrain files use these height-grid constants:

xxxxxxxxxx
N = 257
MAIN0 = 594
SKIRT = 3840

The playable center terrain is a 257 x 257 height grid divided into 256 patches:

xxxxxxxxxx
16 x 16 patch grid
17 x 17 vertices per patch

For the embedded Nation24 scaffold, the center patch indexes are:

xxxxxxxxxx
patch indexes MAIN0..MAIN0+255
patch indexes 594..849

However, arbitrary compiled National .trn files do not have to use those fixed patch indexes. Observed examples:

xxxxxxxxxx
FireRoad.trn            patch_count = 858, center patches 594..849
BaatKips_SX2K.trn      patch_count = 346, center patches 86..341

Readers should locate the center terrain through the tail / quadtree leaf patch references instead of assuming MAIN0=594.

When fixed MAIN0 indexing is known to apply, patch grid mapping is:

xxxxxxxxxx
local_patch = patch_index - MAIN0
patch_col = local_patch % 16
patch_row = floor(local_patch / 16)

grid_x = patch_col * 16
grid_y = patch_row * 16

Span 2 of each center patch contains the height and normal records used to reconstruct or modify the center terrain.

Center Patch Discovery from Quadtree

The tail / quadtree contains leaf records with world-grid coordinates and patch references. For extraction tools:

1. locate tailStart after the texture section

2. recursively walk quadtree nodes from the root node at tailStart

3. follow child-table offsets when present

4. collect leaves with their ox, oy, and patch index fields

5. find the 16 x 16 block of leaves covering a 256 x 256 center section

6. sort the selected leaves by oy, then ox, to rebuild the 16 x 16 patch grid

The quadtree leaf fields needed for center-patch discovery are:

xxxxxxxxxx
offset  size  type  field
+28     4     u32   ox, leaf X grid coordinate
+32     4     u32   oy, leaf Y grid coordinate
+40     4     u32   patch index
+56     4     u32   child table offset, or 0 for leaf

The selected center block can be offset by one 16-cell patch from the logical center. Observed examples:

xxxxxxxxxx
FireRoad.trn        center block origin = 496,496
BaatKips_SX2K.trn  center block origin = 512,512

This matters for extraction orientation. A display/export tool may need to apply a cyclic 16-pixel patch-edge wrap derived from the block origin rather than applying the same wrap to every track.

Center Patch Vertex Records

Decoded span 2 for a center patch contains 17 x 17 vertex records. Each record is 16 bytes:

xxxxxxxxxx
offset  size  type   field
+0      2     bytes  inherited template data
+2      2     u16    encoded_height
+4      4     f32    normal_x
+8      4     f32    normal_y
+12     4     f32    normal_z

Terrain writers update encoded_height and the three normal fields.

Height Encoding

Terrain writers resample source terrain to 257 x 257. One common encoding strategy finds the minimum height and uses the floor of that value as the terrain base:

xxxxxxxxxx
base = floor(min_height)

Each height is encoded as:

xxxxxxxxxx
encoded_height = round(256 * (Z - base) + SKIRT)
encoded_height = clamp(encoded_height, 0, 65535)

Writers must keep patch-grid orientation consistent with their source height array. Existing files may require orientation correction when extracting a TGA for image editing.

For tools reading an existing .trn, the raw height values can be converted back to feet with:

xxxxxxxxxx
ASC_Z = Base + ((raw_height - 3840) / 256)

The .trn does not store the original .ter Base plainly. If the original .ter is unavailable, extraction tools must choose a reconstruction Base. One practical approach is to target a darkest editable TGA gray value, such as 55, then solve for a matching Base and suggested Tga2Asc.exe maxheight.

Extracted Displacement Orientation

Decoded TRN patch order is not always the same orientation as a TGA shown in a normal image editor. For FireRoad-style extraction, a useful default is:

xxxxxxxxxx
default orientation = flip vertical

Then it applies a quadtree-derived cyclic patch wrap when the selected center block is offset from 512,512:

xxxxxxxxxx
wrap_x = (512 - center_block_x) mod 257
wrap_y = (center_block_y - 512) mod 257

Observed examples:

xxxxxxxxxx
FireRoad center block 496,496       wrap_x=16, wrap_y=241
BaatKips center block 512,512       wrap_x=0,  wrap_y=0

The wrap is an extraction/display correction. It should be derived per track; applying FireRoad's wrap to every National TRN misaligns tracks such as BaatKips.

Normals

Normals are computed from the 257 x 257 height grid using neighbor samples:

xxxxxxxxxx
dx = (height[x+1, y] - height[x-1, y]) * 0.5
dy = (height[x, y+1] - height[x, y-1]) * 0.5

normal = normalize(-dx, 1, -dy)

Edges clamp to the nearest valid grid coordinate.

Texture Data

After the patch data, the texture block has this observed National layout:

xxxxxxxxxx
u32 K = 16
u32 G = 1

u32 perimeter_width = 64
u32 perimeter_height = 64
u32 inherited_perimeter_field
u8  perimeter_indices[64 * 64]
u8  perimeter_mip[32 * 32]

u32 main_tile_width = 256
u32 main_tile_height = 256
u32 inherited_main_field
u8  main_tiles[16][256 * 256]
u8  main_mips[16][128 * 128]

The parser names the inherited third texture-header fields g3 and k3. Their values are read from the template and written back unchanged.

For extraction/display, the reconstructed 4 x 4 1024 x 1024 texture needs a vertical flip to match the source texture orientation shown by common image viewers.

Texture Pipeline

A common texture build pipeline is:

1. quantizes the main terrain RGB image to the requested color count

2. builds the 768-byte RGB palette

3. builds both shade lookup tables

4. resamples the main terrain texture to 1024 x 1024

5. flips the main texture vertically

6. palette-maps it to 8-bit indices

7. splits it into 16 256 x 256 tiles in a 4 x 4 layout

8. creates one 128 x 128 mip for each main tile

9. resamples the perimeter texture to 64 x 64

10. palette-maps the perimeter texture

11. creates one 32 x 32 perimeter mip

Tail / Quadtree Offsets

After replacing color-mapper, patch, and texture data, the tail section may move to a new byte offset. Writers must relocate affected tail pointer locations by the same delta.

The tail walk starts at tailStart. Each node is treated as a 15-field little-endian u32/i32 structure for the fields relevant to patch discovery and bounds repair:

xxxxxxxxxx
field 2   bA, signed bounds value
field 3   bB, signed bounds value
field 4   dmax / LOD error, left unchanged
field 10  patch index for leaves, or 0xffffffff
field 14  child table offset, or 0

When field 14 is non-zero, it points to a 256-entry child table of u32 offsets. Non-zero child offsets are recursively walked and relocated.

Bounds Patching

The embedded Nation24 scaffold includes quadtree / LOD bounds for the original terrain. If the new terrain is taller or shorter, stale bounds can cull polygons incorrectly. Writers can repair bounds after recompiling:

• decode span 2 of each center patch

• read all 289 encoded_height values

• compute each center patch's min and max encoded height

• for center-patch leaves, write those exact min/max values to fields bA and bB

• for internal nodes, expand stored bounds to include child bounds

• leave dmax unchanged

This operation only expands ancestor bounds. It is intended to reduce incorrect culling without changing the template's LOD behavior.

.TRN Reader Behavior

A .trn reader should:

• parse the header and optional color-mapper section

• locate the patch table and patch spans

• detect raw vs compressed spans

• decode compressed spans with MCM LZW

• locate texture data and preserve inherited texture header fields

• locate the tail / quadtree start

• walk selected tail offsets for relocation and bounds patching

• read the quadtree recursively

• discover the 16 x 16 center patch grid from leaf patch references

• reconstruct a 257 x 257 displacement map from span 2 height records

• infer .ter GridResolutionInFeet from the TRN scale field

• suggest Tga2Asc.exe maxheight and .ter Base from raw height range plus an editable darkest-gray target

• reconstruct the 1024 x 1024 texture from 16 palette-indexed tiles

• flip the texture vertically for source-image orientation

Fields not used by known readers or writers remain undocumented here.

National Track File Set

A complete National track project may contain:

xxxxxxxxxx
<baseName>.scn
<baseName>.dat
<baseName>.trn
<baseName>.asc
<baseName>.ter
<baseName>.tga
texture.tga
texturea.tga
tile.tga
tilea.tga
README.txt

The game-file subset is:

xxxxxxxxxx
<baseName>.scn
<baseName>.dat
<baseName>.trn
<baseName>.tga

The .asc, .ter, texture*.tga, and tile*.tga files are MakeTerr source assets. The game-file subset is what MCM1 needs at runtime.

Relationship to MakeTerr

National terrain can be built through the National MakeTerr workflow using a National .ter file and referenced ASC/TGA assets:

xxxxxxxxxx
height source + texture images
  -> 257 x 257 ASC-style height grid
  -> 1024 x 1024 indexed texture tiles
  -> compiled National TRN

The National .trn format is not interchangeable with the Supercross / TrackEdit .trn format. Supercross uses a different terrain type, different height encoding, different patch counts, and a different .dat format.

National Toolchain

The historical National track workflow used several small tools and 3D Studio Max plug-ins. These tools are useful when rebuilding terrain externally or working with original National authoring assets.