Automatical Vectorization

Loading Raster Image into GPS

Automatical Vectorization

Click here to download sample file in *.img format
(GPS supporting user styles is required to use this file)

Updated 28.04.2008 - more colors supported, faster processing, faster rendering in GPS, automatical image colors reduction and resampling

This function can be accessed via main menu > Image > Automatical Vectorization. It allows to create map for GPS from satellite images or scans automatically, within a few minutes. It is intended for use in situation when there are no vector maps available of the area of interest, and drawing of precise vector map is not efficient either because of lack of time or limited use of the map.

In fact, Garmin units do not allow to load raster image into GPS and use it as a map. This function automatically vectorizes raster image and creates vector file compatible with GPS. Autovectorized maps contain thousands of small color spots and are large is size and slow to render on GPS, therefore.

Objects automatically vectorized from raster image.
Map consists of large number of polygons.
Colors are derived from raster and included into "User defined styles"
for optional manual tuning and/or transfer to other map file.

Examples of autovectorized maps in GPS

Pros: almost "one-click" process to create ready-to-use GPS map. You can create map like above examples in a few minutes. Auto-vectorized map can be combined with waypoints, tracks, manually drawn objects or other map data (like merged shapefiles, etc.)

Cons: GPS must support user defined styles (most of new units support them). Auto-vectorized map file is larger than normal map file and its rendering in GPS is slower. Auto-vectorized map does not allow to search objects. Objects do not have names, hints and other attributes. In other words, this kind of map is for viewing only.

Technical notes

Auto-vectorized maps were successfully tested on Colorado, Nuvi, GPSMAP 60CSx, Street Pilot c550.
Number of auto-vectorized maps can be loaded into GPS at once. Auto-vectorized maps can be exported into IMG format and combined with any other GPS maps. However, they must use the same set of user defined colors. To achieve this goal, use paletted images with same color palette. Current version of Mapwel supports max. 86 colors for autovectorization.
Warning: you have to set map detail in GPS to 'Most' (default value is 'Normal') to see autovectorized map in full detail. Otherwise, only a large colored squares are visible. Autovectorized map is supposed to be rendered in full detail at zoom 800 m and closer.

Map setup menu with Detail option.
This is screenshot from Colorado 300, but each Garmin GPS has some menu for setting this option.
Make sure to set it to 'Most'.

How to use auto-vectorization

Use any image editing software to resample and crop raster image. Reduce number of colors to fit into range supported by Mapwel (up to 86). Save image into GIF, PNG or BMP format.
Import image into Mapwel. If number of colors exceeds max. allowed number, Mapwel automatically reduces number of colors during autovectorization.
Georeference the map. You can skip this step if you import OziExplorer callibrated image.
Use main menu>Image>Automatical Vectorization function to create map.
Send map from Mapwel to GPS.

How to reduce number of colors in an image

To use image for automatical conversion into vectors, you may need to reduce number of colors. Mapwel reduces number of colors automatically, but you may need to use the same color palette for several images. In such a case, reduce colors manually, save the color palette and use it for other images too.

If you have Adobe Photoshop, you can use following approach:

1. Use Photoshop > main menu > Image > Mode > Indexed Color to open window for color reduction.

2. Select no dither, no transparency and set required number of colors Select any type of palette that works best for your image.

3. Image with reduced number of colors lacks blue color for pool. We will add it manually. Undo the color reduction and repeat step 1. However, select 'Custom' palette in this case. Please note: in this simple example number of colors is reduced to 9, but Mapwel supports much more colors.

4. Custom palette contains 9 color automatically selected in previous color reduction. Add light blue color as 10th color into palette and click OK. Image now contains 10 colors and light blue is among them. Save image into BMP, GIF or PNG format to avoid colors distortion (do not use JPG format for the same reason).

Click here to download sample file in *.img format
(GPS supporting user styles is required to use this file)

	Mapwel - free demo MAPupload (allows to add your map to maps in GPS memory)