OSM Tools
dutch german en francais spanish polish polish russian

Exploring IMG Format

TYPWiz 7

Advanced UTF-8 unicode TYP editor

For more information check out here

Quickly change your current map into any colour scheme!

What is NT IMG format?

Many of the new features are a result of car sat nav development.

1) Routing is more compacted

2) Includes multiple lane routing/switching on a motorway

3) Handles Junction View (JCV), pictures that popup at junctions, stored as a SVG (text) file

3) polygons can have height to enable 3d structures

4) Searches include Post Codes

5) Can contain raster images(jpgs)

6) Extra POIs and Active Routing

7) Better support for non english/american labelling

Some details regarding NT POIs have been reversed engineered here


RGN Header

RGN Offset RGN Header
00 Header Length
15 Pointer to beginning of RGN1 data, ie first subdivision to include possible POIs,Indexed POIs,Polylines or Polygons or first map level
19 Length of this block

Pointer to RGN2 data block,contains polygons with extended types 0 x 100+ ; for undocumented details about its structure see Exploring IMG Format

21 Length of this block
39 Pointer to RGN3 data block ; this block contains polylines with extended types 0 x 100+ ; for undocumented details about its structure see Exploring IMG Format
3d Length of this block
55 Pointer to RGN4 block containing extended POIs ; for undocumented details about its structure see Exploring IMG Format
59 Length of RGN4 block


The NT poi file structure is slowly revealing itself - more here

Exploring IMG Format

How to plot highways etc

Find out ,step by step, how highways,polygons and pois are plotted in a Garmin IMG file and how names/labels are stored/unzipped.

Exploring IMG Format focuses on the RGN ,TRE LBL NET & NOD subfiles and includes various undocumented blocks in the RGN & TRE subfile using numerous examples to make its complicated structure more accessible.

It also explains how TOPO files are locked and what can still be retrieved.

Maplevels & Subdivisions

Maplevels are like zoom levels. Each map level contains a group of subdivisions. The last map level in an IMG file holds the most detailed subdivision(s) which unlike the earlier ones generally do not need to be left_shifted.

Offset 0 x 15 points to the first maplevel / subdivision as defined in TRE. with additional information in Exploring IMG Format

It generally starts with 2 byte offsets to a different element type , ie polylines or polygons,within a given map level block. If just one element, ie polylines, is found ,then the subdivision contains no offsets.


28 00 35 01 64 12 00 00 5e FF BD FF 17 64 CF 00 80 7A 00 94 FF 0F

Pointers are highlighted in bold:


Checkout Latest NT findings


More information in the following document:


Download Exploring IMG Format (pdf)


(latest with info on FID and PID & TRE SEP 3 2012)


Garmin GPI Files (POIs for Car/Bike Satnavs)


More information about its file structure




Click here to check out JCV file structure