Garmin QuickDraw on a 93sv-results

[skid00skid00]

Got my new 93sv on the water yesterday. Spent a fair amount of time scanning an interesting feature that I found on the 93's included LakeMaster chart.

I wanted to test the hypothesis that using a crosshatch scan pattern wasn't strictly necessary. I found that running parallel paths about 40 feet apart produces good results EXCEPT for the edges of the scanned area. In this test, it seems that you want at least 3 parallel paths to get the correct terrain slope lines. The outermost path's depths will be correct - at the GPS coord the 93sv was over, but since QuickDraw shows contour lines well past the point the boat was over, those edges may/will not show the correct contour.

It's been pointed out in other posts, that when you run a single path, all the contour lines are perpendicular to the path. The program designer made this choice. You cannot plot sloping contours in 2D when you only have 1D measurments!

(I need to spend some time converting the .bmp screencaps to png. Back in a bit...)

[skid00skid00]

OK, here's an example of how the program draws contour lines perpendicular to the path, when it doesn't have enough 2D data:



Add three side-by-side paths, and you can see contour lines parallel to the boat's path:

[skid00skid00]

This screencap shows the default Garmin LakeVu chart image, and QuickDraw:



With paths:


Note that the edges of the QuickDraw chart do NOT show the correct slope. When you chart, you should probably extend the boat path into the flats surrounding the area you are interested in.

[Larry3215]

Thats been noted before. The outer edges of any QD chart will be wrong - unless you are using a PS30. Apparently it can get accurate contours out to the edges of the scan area because it is recording 3D.