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Position errors of marked targets due to heading differences

clock May 15, 2012 21:45 by author SonarTRX

When marking targets visible on sidescan data from the Humminbird/Lowrance sonars, it is important to keep in mind that the boat heading (and normally the transducer heading) is not necessarily the same as the "Course Made Good" (CMG) based on GPS positions.

If the boat is pointing into the wind or strong current in order to stay on track, and the marked targets are far away from the track, this error may be large. The image below illustrates this:

Angle Errors

  • The boat (and the transducer) is pointing to starboard by 20 degrees relative to CMG.
  • The Brown image is calculated based on the assumption that the transducer is aligned with CMG.
  • The Blue images are based on a "pointing angle" of 20 degrees (i.e. you point the vessel 20 degrees into the wind/current in order to stay on track of the survey line)

In essence: When marking a target, keep in mind the heading of the boat relative to CMG and remember that the position of the targets may need to be adjusted for this heading error. If making the marks on the sonar during the survey, it is important to also make a mark at the track-line, since that is the "point of rotation" for this correction. The extent of the search area can then be increased to account for uncertainties in the transducer-angle.

If the boat is drifting while recording, the difference between CMG and the heading of the boat may be very large, and even completely flipped 180 degrees (...drifting backwards). In that case, if you targets are marked at a certain range, the marks may even be interpreted as being on the WRONG side, since there is no available information about the actual heading of the transducer. (i.e. everything is based on the CMG from the GPS)

The SonarTRX images can be corrected for a constant heading differences for a given batch of image-tiles. This is done from the Mosaic creation dialog.

SonarTRX 10.6 Released

clock May 11, 2011 03:32 by author SonarTRX

SonarTRX 10.6 has just been released

For product information and release notes for new and older versions, please visit the main web-site:

Recent SonarTRX Improvements

clock May 2, 2011 22:48 by author SonarTRX

When importing SonarTRX image tiles into GIS programs for assembly and merging into larger mosaics of the survey area, it is important to minimize any "seams" between adjacent image-tiles. The sample below illustrates recent improvements in that regards. The seams in the right side sample are barely visible.

Image Mosaic Improvements

The above sample images were generated with Manifold GIS, after importing 14 tiles from both starboard and port sidescan channels. No slant range correction was applied.

The sub-division of sonar data into image-tiles makes it easier to "mix and match" tiles from several passes over a survey area. As of version 10.5 of SonarTRX, the tiles can be cropped at a certain range, providing additional flexibility when assembling a mosaic of the survey area. The sample below illustrates this feature and how it can be used to avoid overlapping background imagery.

Cropping of image tiles at certain sonar range

Existing customers and partners with a license can request an update by contacting

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Google Earth rendering of SonarTRX images and Navigation settings

clock April 30, 2011 03:13 by author SonarTRX
  1. When viewing the SonarTRX sidescan mosaic image tiles in Google Earth, make sure you turn off the Google Earth image compression, so you avoid artifacts in the rendered PNG images. Click on the Tools - Options menu, and select the 3D View tab. In the Texture Colors area, uncheck the checkbox for compression.
  2. To zoom in on the sidescan sonar image tiles and prevent Google Earth from changing the tilt angle as you get close, turn off the automatic tilt while zooming. Click on the Tools - Options menu, and select the Navigation tab. In the Navigation area, click the radio-box that says "Do not automatically tilt while zooming".

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SonarTRX 10.5 Released

clock April 21, 2011 04:14 by author SonarTRX

SonarTRX 10.5 has been enhanced to support several new user-requested sidescan mosaic processing features:

For product information and release notes for new and older versions, please visit the main web-site:

SonarTRX-SI, a great seabed mapping tool for kayak with Humminbird sonar

clock March 2, 2011 21:47 by author SonarTRX

If you would like to learn more about how you can use SonarTRX to create images of the seabed in your fishing or diving area, please check out the recent article and video by (They use a Humminbird 900-series Side Imaging sonar on an Ocean Kayak.)



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