Format of the Cvx BGL Files

Introduction

CVX Files can be read by the TmfViewer.exe application provided with the FS SDK. They contain TERRAIN_VECTOR_DB sections. These sections and subsections describe the different layers (roads, railways, water polygons, etc.) along with the geographical coordinates.
In this document, I will often take examples from the cvx2815.bgl file since that is the one I used to figure out the structure of the cxv file and it describes the area I live in. This file is located in: (....)\Microsoft Flight Simulator X\Scenery\0301\scenery.

BGL Common Format

All BGL files share the same generic format. A BGL file is made of a header, sections, subsections and subsection data. Subsections are children of sections. The sections are here to help us locate the subsections in the file. Data specific information is contained in the subsections data and their format is dependent on the section type.
A BGL file always start with a header (Size = 0x38 bytes), followed by a list if section pointers. The number of section pointers is defined in the header.