In addition, the software may be used for converting GPS-tracks and waypoints among various formats. In Russia, for instance, the convertor cMap.exe is widely used. It gets maps in GEM/GCT format from Ingit (St.Peterburg). Such maps cover mainly Russian territory. pGPSmap is example of software making some post-processing of Polish files. This utiliy splits map to few parts and diminishes number of points in polygons up to 255, as required by obsolete versions of cGPSMapper.exe. And, of course, you may write you own software based on Polish format! In this case, GPSMap Edit may be used as your covertor’s output verification tool and as source of ready code or parser. However, you may use raster maps in GPSMap Edit as base for manual drawing of vector ones over them, both and to fix existing vector maps. GPSMap Edit is freeware whixch opens GIF files for reading only. Futhermore, it really does not include any code implementing LZW decoding algorithm, but uses external code embedded in Windows (which is licensed by Microsoft). In addition, Unisys’ patent will expire in 2003. In general, map contains a few zoom levels for different scales. The levels are defined in the header of map (section [IMG ID]) through parameters ‘LevelX=’, ‘ZoomX=’. If all objects belong to one of level (e.g., to 0-th one), the window will be empty for all other scales. You may delete the empty levels to solve the problem. (NOTE: less detailed level should be always empty, according to cGPSMapper’ documentation, so minimal number of levels is two). Note that some of Garmin models never visualize some types of regions at all. For instance, city blocks are not shown in eTrex Vista. Moreover, some important kinds of objects have no corresponding region type in Garmin’s GPS-navigators. Examples are railway/subway stations, squares, buildings (as polygons) etc. In contrast, TXT files imported from IMG always contain single-element objects. (The intrinsic reason is in IMG format details.) This provides some kind of ‘traps and pitfalls’ for users while editing. So, the ‘Join region levels’ function combines similar objects from different levels to the joined objects. The ‘Split region levels’ one breaks the objects to per-level parts back. In general, affine transformation may be specified by three pairs of points, each pair consists of source point and destination one. In particular, both points of a pair may be equal meaning no shift at the place. If points are equal two by two in each three pairs, the transformation changes nothing. To apply an affine transformation to a map, you should have some high-precision geodetic data for the calibration. These may be a raster map (OziExplorer) which is tied as well or tracks and waypoints obtained using GPS-navigator. It is important to make sure that all coordinates are presented in the same datum or be able to convert to WGS84. You may freely change tools temporarily during preparing to affine transformation – to ‘Drag’ tool or to ‘Select’ etc – and go back to pairs defining. It is recommended to define pairs as distant as possible from each other and from center of the map. This may provide higher accuracy. For instance, Russian maps are based on ‘Pulkovo-1942’ datum. The one used in GPS is WGS84. In Moscow region, they are shifted approximately in 150 m. To avoid loss of GPS precision (wich is about 15 m) you should always make sure that all coordinates are defined in or converted to the same datum. Source.