CFU RASTER FORMAT SPECIFICATION

Transcription

1 Name: "MyNav CFU format" Version: 1 MyNav compatibility: v and above Date of publishing: November 18 th, 2010 Introduction CFU RASTER FORMAT SPECIFICATION The MyNav raster format is compatible with MyNav devices, PDA and Desktop PC running MyNav (or higher). The MyNav raster includes calibration data files and image tiles, and it is capable to handle different layers. A raster map overlaps the standard vector MyNav map and its bounds need to be entirely included into the vector map. If there is no vector map it is still possible having raster images creating an empty bounded map (called User Grid ) by using the Map Manager software (v or higher). The scope of this document is to specify the complete MyNav raster format, allowing the reader to create a raster map from scratch, also with an example as tutorial. Source Map The original source map is a georeferenced image (with an establised location in terms of map projections or coordinate systems) of any type and dimension. To get the best quality of the final raster map and optimize the conversion processes, there are a few things to be aware of: - projection - resolution - size - colours Projection Raster maps and vector MyNav maps come from different sources, therefore it become essential to have a common referencing system when they are combined. Vector maps are represented in custom UTM over ED50 projection with central meridian passing through the centre of the map to avoid and minimize distortions. For example, MyNav Europe map is projected on UTM Zone 32. Even if the coordinates in the CFU calibration data file are in WGS84, the best results are obtained starting from a source already projected in UTM, because the WGS84 coordinates will be converted in the correct UTM zone by the engine. Resolution Even if there is no theoretical limit to the resolution of the source map, it should be noted that MyNav most detailed view is optimized for 1:2500 data. Showing a detailed map at lower scales can create bad aesthetics due to automatic resize of the image. Similar problems can arise when showing a low resolution image at very high scales (maximum zoom levels). A proper usage of the multiple layer system can reduce these issues still letting the user to view a nice map smoothly from 1: to 1: For example, it is possible to use a detailed with resolution of 0.5m/pixel to be view only from 1:50000 to 1:2500, while another source coming from a 1: map to be view from 1:50000 to 1: in MyNav software. For limiting the resize issues, it is not advisable (but still possible) to use images more detailed than 0.5m/pixel. Size

2 To get the best performance, a big original source should be tiled in smaller parts. Image tiling procedures are out of scope of this documentation, but the tile technical specification will be discussed in a following chapter. Colours The MyNav raster format is limited to 8 bit colour depth, that means max 256 colours per tile. This means that if the original source map uses more colours, it is possible that in the final raster map there will be a sort of degrading of the quality. Anyway, as the drawing engine works per tile, it is still possible to define different palettes for every tile of the image, giving theoretically an infinite colours model. The suggestion is to downgrade the depth in creating tiles using professional software that can optimize the loose of colours without impacting the overall image quality. There is also the possibility to use a transparent colour that will not be drawn in the final map, to make possible to create not-rectangular boundaries in the final maps. By default, all the colours are opaque. Map Tiling The source map should be divided in smaller tiles, that will be directly handled by the drawing engine. The format of the tiles is BMP (bitmap) with 8 bit/pixel depth (256 colours), not compressed. To optimize the tile handling, the size of a tile is limited to 1Mbyte, equal to a tile with maximum pixels. The tile should be bigger as possible to limit the file loading overhead. The tile can be square or rectangular; for square tiles, the pixel size should be equal or lower than 1024x1024, for rectangular tiles the rule is width * height <= Tile format: BMP 8 bit not compressed - Maximum storage size: 1MB, equal to a 1024x1024 square tile - Pixel size: 1024x1024 square tile, or rectangular tile with maximum pixels (i.e.: 2048x512) Once ready, the file can be put on sub-folders. For example, the following are valid tile names: bmp - t_2048_1024.bmp - 02/test.bmp - orto25/gm31_kmz_l3_0_1.bmp One suggestion is to create a small overlap border in the tiles to overcome the small artefacts that can appear in rotating the images. A typical overlap of 2 or 3 pixels should be enough. Multiple Layers MyNav can handle up to 10 raster layers, where each layer consists of a single calibration file. Each calibration file specifies : - scale range of visibility for the layer (ex.: from 1: to 1:2500) - image tiles belonging to the layer and their coordinates The layers will be shown in order, depending of the layer calibration file name. The file name must be - RASTER.cfu (for layer 0) - RASTER_N.cfu (for layer N, with N = 1..9) If two or more layers contain the same map zone for the same scale, the drawing order depends by the layer number. The engine draws first the layer 0, then layer 1, etc., so the visible layer will be the layer with highest number, as follows:

3 If defining a map with M layers, all the configuration files from layer 0 to M-1 must exist. For example, if there are 3 layers, there must be RASTER.cfu, RASTER_1.cfu, RASTER_2.cfu; for only one layer, RASTER.cfu is enough. Calibration Data File For each layer, a proper calibration data file must be defined so the drawing engine will have the information about georeferencing the tiles. This is the core of the CFU raster format. The starting file is a plain-text ASCII file with a header line that specifies the range of visibility of the layer, followed by the list of tiles with boundary coordinates. The file should be named RASTER_N.cfu as specified in previous chapter. RASTER_VERSION line The first line must be in the form: transparent_colour where version (currently is 1 ) is needed by the drawing engine to parse correctly the following data. transparent_colour (optional) is decimal form of the COLORREF (BBGGRR) definition of the pixel to be processed as transparent. Example: means that the version is v1 and the custom transparent colour is or hex 0x65D284 (Blue: 0x65; Green: 0xD2; Red: 0x84). RASTER_SCALE line The second line specifies the range of visibility of the layer, and it is in the form: b where a (should be > than b) is the lower visibility scale for the layer (i.e.: a = means 1: , or 1cm = 10km). Values range from to 0. b (should be < than a) is the higher visibility scale for the layer (i.e.: b = 2500 means 1:2500, or 1cm = 25m). Values range from to 0. Example: means that the layer is visible from when 1cm=1.5km to when 1cm=25m. RASTER line The following lines in the file specify the georeferencing of the tiles, giving details to the bounding box coordinates for each tile. The lines are in the form: RASTER y3 where tile_name is the full name given to the tile, with the relative path in case of sub-folders (using the / symbol for directories)

4 x1 specifies the longitude of the point P1 of the tile, in decimal degrees from 0 to ±90 y1 specifies the latitude of the point P1 of the tile, in decimal degrees from 0 to ±90 x2 specifies the longitude of the point P2 of the tile, in decimal degrees from 0 to ±90 y2 specifies the latitude of the point P2 of the tile, in decimal degrees from 0 to ±90 x3 specifies the longitude of the point P3 of the tile, in decimal degrees from 0 to ±90 y3 specifies the latitude of the point P3 of the tile, in decimal degrees from 0 to ±90 P1 is the point at the upper left corner of the tile, at pixel coordinates (0,0). P2 is the point at the lower right corner of the tile, at pixel coordinates (width, height). P3 is the point at the lower left corner of the tile, at pixel coordinates (0, height). Example: RASTER means that the tile bmp in folder 02/ has the left upper corner at Lat Lon and the lower right corner at Lat Lon Using the Raster Map When the tiles and the layer configuration files are ready in a named folder, it is enough to copy the folder into the <SD Card root>\my Raster\ directory in the device, or into <installation dir>\my Raster\ directory in the PC. The raster map will be then visible to the MyNav drawing engine. To see the raster on the device, go to Menu Settings Map Elements Show/Hide Raster and look for the name given to the raster folder. Check it, Save and go to Map in that zone. The raster images have a lower priority respect the vectorial layers, so they can be partially covered by vectorial polygons like Hydrograph, Urban Areas, Green Areas. If needed, turn off vectorial layers in Menu Settings Map Elements Show/Hide Layers to see the raster map.

5 Example The following example is presented in this chapter: a small raster over Valladolid, Espana, divided in two layers, with tiles of different size. The chapter presents the description of: - Files structure in PC - Layer 0 configuration file: RASTER.cfu - Layer 1 configuration file: RASTER_1.cfu - One layer 0 tile example: test_13.bmp - One layer 1 tile example: test_18_(0).bmp - MyNav screenshot at 1: MyNav screenshot at 1:5000 The same data should be available as a archived valladolid.zip file together with this document. Files structure in PC Directory of C:\Programmi\Giove Srl\My Raster\Valladolid 23/06/ <DIR> 13 23/06/ <DIR> 18 23/06/ RASTER.cfu 23/06/ RASTER_1.cfu Directory of C:\Programmi\Giove Srl\My Raster\Valladolid\13 23/06/ test_13.bmp Directory of C:\Programmi\Giove Srl\My Raster\Valladolid\18 23/06/ test_18_(0).bmp 23/06/ test_18_(1).bmp 23/06/ test_18_(2).bmp 23/06/ test_18_(3).bmp 23/06/ test_18_(4).bmp 23/06/ test_18_(5).bmp Layer 0 configuration file: RASTER.cfu RASTER Layer 1 configuration file: RASTER_1.cfu RASTER RASTER RASTER RASTER RASTER RASTER One layer 0 tile example: test_13.bmp

6 Figura 1: "test_13.bmp", full size One layer 1 tile example: test_18_(0).bmp Figura 2: "test_18_(0).bmp", 33%

7 MyNav screenshot at 1:50000 Figura 3: MyNav showing layer 0 at 1:50000

8 MyNav screenshot at 1:5000 Figura 4: MyNav showing layer 0 at 1:5000