Lowrance HDS and Elite HDI units can show images of any sort as part of a map, and combining a background image with a vector overlay to show depths can produce great maps that can be really useful in fishing situations. The sort of images you might want to be able to see your on unit include satellite imagery, scanned topographic maps, sidescan image mosaics etc.
In this example we are going to combine a side-scan mosaic image created by DrDepth (ReefMaster doesn’t do side-scan mosaics yet – but it’s coming soon!) with a vector overlay created in ReefMaster.
1. Create the raster background files
The
Insight Map Creator from Navico can be used to create raster backgrounds for your unit, using any geo-calibrated image that you can provide with a KML or PGW calibration file (KML is a commonly used file format native to Google Earth, and many tools exist that will convert geo-calibrated files in other formats, e.g. geoTIFF, to KML).
We are using a side-scan image mosaic that has been exported from DrDepth as a PNG image file with an associated Google Earth KML file.
Start the Navico Insight Map Creator application, and switch to raster mode.
We need to let the IMC know which files to process. Note that the IMC accepts folders for raster mode (not individual filenames), and will process all image files within the specified folder(s), so the easiest thing to do is make a new folder which contains just the KML and image files.
Set an appropriate min and max resolution:
The Min and Max Resolution values refer to pixels per metre of your original image. The IMC will rescale your image to match the values you use. To determine the native resolution of your image, divide the width in pixels by the width in metres. You can find the width in pixels by right-clicking the image in Windows explorer and looking at the properties. It is not necessary to a value as low as your native resolution, but you will lose some detail from your image at higher zoom levels if you do not. Note that very high resolution images (with low pixels-per-metre value) can take a long time to process. The upper limit is a matter of preference – the higher the value, the lower the zoom level required to see the image in the unit. The downside is that the image will be set in a “tile” that will obscure other map components, and this tile will cover larger areas at higher resolution settings. A value of 8 is a good starting point.
Set your work directory, and click Build
Once the build completes, there will be some output files in a directory called "BoundAT5s" sitting underneath the specified build directory. These images should be copied to a map card in a directory called "ShadedRelief" located at the root of the card.
2. Create the vector overlay.
Generate the map project of the area in
Vector mode. Vector mode is important here if we want to see areas coloured by depth in the finished map. We cannot use a raster background, as that would obscure the image background that we exported in step 1.
Choose an AT5 compatible palette now (unless you want to style the map areas individually in the user map) and select the right-click-menu option
Add components to map.../Add components…/New User Map.
Here, the background image that we have already processed in the IMC has also been imported into ReefMaster (option
New Image, and select the KML file – not the image file). This helps us see how the finished map will look on the unit, but is not required as part of this map create process.
Set the transparency of the depth areas
All we need to do to this map before exporting it is to set the transparency of the depth areas, so that we will be able to see the background image through the coloured depth areas in the GPS unit. Choose a value for the opacity field, where 1 is fully transparent and 255 is fully opaque, and export the map from ReefMaster by right-clicking in the user map view and selecting the option Write to File. Make sure that the option “Export Raster background” is not selected, as we do not want to overwrite our existing background image, and click save and select the root of your memory card as the save location.
This is how the map looks on a Lowrance HDS 5. We now have the best of both worlds – a background image showing features on the bottom, and depth area colours on top.
Note that if we want, we can turn the coloured depth areas on and off using the
Chart Categories feature on the unit. We can do this whilst on the water, whilst keeping the depth contours visible (these can also be turned off, if required). The category for depth areas exported by ReefMaster is
(AREA)Nautical/Depth.
In this example the style of the contours in the user map has been changed to make them thicker and more visible over the background image (the width and colour attributes of the
Major Contour group in the user map).