- Digital Charts of Lough Corrib


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Creating Bathymetric GPS Charts – the simple way

How the Chart is made

While there are plenty of methods of creating bathymetry, the following method is probably the cheapest! We still use this method ourselves for areas where other methods are restrictive and where the software still isn’t as good as the human brain at puzzling out the nature of the lakebed

Software required
1) GPSMapedit -
2) Mapsource
3) GPS Utility -

Download Sample Files

Make sure that in
GPS Utility under 'Options => Field Properties' that the primary field is set to "Altitude", and the secondary field is set to "Depth". Under 'File => Export Options' make sure that shapefiles are set to "export as points"

Download your GPX file from the GPS into Mapsource and save it as a .gdb file

Open it in GPS Utility - if you have it set up correctly this is what you’ll see
(Click on image for full-size preview)

This next step is a bit of a kludge – but it works

Now go to 'Tools' - “Swap Altitude – Depth” and you now have this
(Click on image for full-size preview)

Under 'File => Export Options' make sure that shapefiles are set to export as points

Next 'File => Save as' and select “Shape trackpoint fileset”

Now fire up GPSMapedit – it’s best if you can have 2 instances of the program running – even better if you can have one on each of 2 screens. Into one instance load your working project, into the other instance start a new file. If you like you can copy a section straight across from your project file to make things clearer. The great thing about this is that the memory is shared, so you can copy and paste directly from one instance into the other with no loss of data or position

Now into the new GPSMapedit file import the shapefile you created

Select the type of object you want (I’m selecting the Garmin Invisible depth point)

Then in the next screen select the “Altitude” field for labels

Click straight through. Your Coordinates and Datum screen should look something like this...

You probably don’t want soundings on all levels, so select only the levels you need

Now click through – and our soundings now appear as labelled points on the chart

Getting the data you need

Let’s say that we consider anything under 5ft to be hazardous (or good fishing) – so we’ll make a 5ft contour. This is simple enough by eye, we have enough soundings here to get a reasonable contour line, probably not enough for a decent survey, but very useable all the same.

So make your contour and give it a label of 5

Now right click on the contour and copy it onto the clipboard. Move your cursor into the other instance of the application you have running, the project file, and Edit – paste. Your contour is now where it should be

Now back to the new file – the one we loaded the shapefile into – and hold down the ctrl key and select any representative depths you want for your chart and then copy them to the clipboard

Paste them into the project chart

Due to the way the Garmin units display these depth, they won’t actually work properly like this, so we have a little work to do on each one

In the project instance of GPSMapedit double click on your new sounding, and select the “extras” tab. The label for the sounding in the example image was -5.9, so click on “edit as text” then enter “depth=5.9” – no spaces, no minus sign – and click OK

If you are compiling this for a G2 unit, go back to the properties tab and delete the label that says -5.9 and click OK.

The label now disappears. This is an unfortunate gremlin with GPSMapedit, and it is not possible to have it display the label for this particular object (the 0x10301 invisible depth point) if the intention is to use the chart on a G2 unit. The sounding will of course work properly in Mapsource and on your GPS. If you leave the label, on a G2 unit the sounding will appear as a very large untidy label

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