Using Triton Mosaic Basic™

 

Mosaic Basic is an optional module of MBSS-Logger (Triton Isis) and SS-Logger.  It allows the creation and saving of Side Scan Sonar mosaics; either as a GeoTIFF image or as a .DDS_VIF layer for further processing in Triton Map™.

 

It is included in the Triton Office Processing suite called Triton SS-Office™, which is comprised of Triton SS-Logger for Playback™, Triton Map™ and TargetPro™

 

The module has previously been know as “Preview Mosaic” and “Quick Mosaic”

Simple Mosaic Creation

 

The remainder of this description assumes that the file has:

 

 

See separate documentation that covers altitude tracking, slant range correction and TVG / Threshold setup.

 

Start SS-Logger (or MB-SS-Logger) and start playing back a file:

<spacebar> pauses playback, <home> takes you to the start of the file.

 

 

Click Tools >

 

 

Coverage Map and Mosaic

 

 

And select “Preview mosaic with coverage map”

 

NOTE:  Windows 2000 and Windows XP are fully supported, however Win95 or Win 98 are NOT.

 

Click OK

 

 

The coverage map window and Preview Mosaic dialog box will open.

 

 

 

Right Click anywhere on the waterfall display to open the Waterfall Display dialog box, and check the Slant range box.  Continue to play back the file.

 

 

The mosaic is generated in the Coverage Map.

 

Depending on the quality of the navigation the image may initially look “broken”, it is almost always necessary to smooth the navigation.

 

 

Click the Nav menu item in the Coverage Window and select Smooth Navigation

 

 

 

 

In most cases the default smoothing settings will work fine, however:

 

If the vehicle from which the data were acquired was traveling very slowly (for example an ROV) you may need to lower the Min speed setting, on the other hand if the vehicle was a hovercraft or nuclear submarine you may need to increase the Max speed value…

 

You may click the Smooth Now button as many times as you wish, each time the smoothing algorithm will be applied and the result seen in the display.  It is advisable only to use the minimum amount of smoothing to obtain an undistorted image.  In some cases where the navigation in the file is of very high quality (for example AUV data with processed navigation) it may be best to set the number of points to 1 which equates to “no smoothing”

 

Clicking Unsmooth restores the raw navigation track.

 

Click Close

 

 

If you want to add more files click No, if you have all the files you need in your final image and want to proceed to the next task, click Yes.

 

Saving the Mosaic

 

Click Mosaic/DTM and select Save RealTime Mosaic

 

 

At this point you need to decide which format you want your mosaic to be in.

 

 

If you have a Triton Map™ license (part of Triton SS-Office™) the best option will be to choose Save as DelphMap DDS_VIF file, if you do not then the obvious choice is Save as TIFF (GeoTIFF)

 

Maximum size of saved Mosaic

 

At the time of writing there is a limitation of approximately 10,000 pixels x 10,000 pixels to the size of the saved image.  The default resolution in Mosaic Basic is 0.25m which limits the mosaiced area to 2.5 square KM  (about 1.3 square nautical miles)   However as we shall see, it is very easy to export a larger area in smaller pieces and merge them together in Triton Map.

 

Note that the size of the mosaic that can be displayed in the coverage map is much larger and can be made larger still by increasing the size of the temporary Memory File.  (see Advanced mosaicing)

 

Saving a DDS_VIF file for Triton Map™

 

Choose Save DelphMap DDS_VIF file > Save Now

 

 

The Dialog Box Map and Projection Settings will open, in the example shown the navigation units are Degrees Lat/Long; you must choose the correct UTM zone for your exported file.  Note the Long value in the Isis Navigation window, in this case 8.759… or about 9 deg East, which means the DDS_VIF file will fall in Zone 32 (between 6 East and 12 East).  If the data are from the Southern Hemisphere check that South Hemisphere is selected.  Click the Change button for the output projection and select Zone 32 as shown, hit Next and Next (assuming WGS84 for the Datum) and Finish.  There may be a long pause at this point while the various projection settings are checked.  Finally click OK in the Map and Projection Settings dialog box.

 

NOTE: If the area chosen is too large an error message will be generated at this point, you will need to select a smaller area for export (see advanced Mosaicing)

 

A standard Save As dialog will open; enter the name of the file and Save.  The resulting .DDS_VIF file can be inserted directly into TritonMap.

 

Multiple smaller mosaics can be inserted into TritonMap, merged together and exported as much larger GeoTIFFs later from Triton Map.

 

Saving a GeoTIFF image.

 

Choosing Save as TIFF (GeoTIFF) simply opens a Save As dialog box:

 

 

 

Mosaic Basic will assume that the projection of your mosaic is to be UTMs and will automatically choose the correct Zone.  The output in this case will be a TIFF image and an associated .TFW (World File) in UTM grid coordinates.

 

Note that the TIFF image in this case does not contain any internal GeoTIFF tags, the .TFW file is always needed for import into other applications. 

 

Advanced Mosaicing

 

There are many other tools in Mosaic Basic, this section deals with the following subjects:

 

.

Exporting larger mosaics

 

You can use the option Export only visible area to export a number of smaller mosaic panels which can be displayed in Triton Map, and optionally merged together to make a larger image.

 

 

 

 

You can use the measuring tool to find out how big your mosaic is and to calculate the size of the resulting image, click and drag the mouse:

 

 

Clearly in the above example the size of the resulting image will exceed the 10,000 x 10,000 limit:

 

The default resolution for Mosaic Basic is 0.25m / pixel therefore this image would be approximately 4,000 / 0.25 = 16,000 pixels wide.

 

An attempt to save the whole image will result is this error message:

 

 

You MUST click NO and either reduce the resolution of the image or choose to export only a part of the image:

 

 

In this case you can see that choosing to export 4 smaller images will keep the size below the 10,000 pixel limit, check the Zoom In button and use the mouse to select the lower right quadrant and then click Mosaic/DTM>Save Preview Mosaic, check the option Save current display area only.

 

 

And Save Now.

 

Repeat the operation as many times as necessary to export the entire area, you can use the coordinate display in Coverage Map for precise export however since the images are georeferenced they will match exactly in a 3rd party application, or in Triton Map.

 

Alternatively you could choose to reduce the resolution to, say 0.50m:

 

 

In the example this action would also reduce the number of pixels in the final image to <10,000 x 10,000.

 

NOTE: You can also click the Cell Size button to have Isis calculate the correct size for each pixel to print a map at a specific scale.  You will also need to know the DPI (dots per inch) of your printer.

The temporary (memory) file

 

When the mosaic is created in Coverage Map it is held in a temporary file.  The size and location of the temporary file is set from the Advanced button in the main Preview Mosaic dialog box:

 

 

The default size for this file is 64MB which will hold quite a large mosaic* in the coverage map window; if necessary the size can be increased.  But you must exit Isis and save the setup to do so.

 

The default location for the file is:

C:\Documents and Settings\<User_Name>\Local Settings\Application Data\Isis

 

NOTES

 

 

Go to the "Advanced" button (see above) and set the memory size to 64MB

 

Also resetting the Path in this dialog box will likely cure the problem.

 

* In the example, a 4KM x 4KM mosaic at 0.25m resolution was accommodated in a memory file that was only 20% of the set 190MB (about 40MB)