Perspective-MB -- Bathymetry Processing Guide -Software Version 7.6 By: Tony M.
Triton Imaging Inc. Engineering Office 2121 41st Avenue, Suite 211 Capitola, CA 95010 USA +1-831-722-7373 +1-831-475-8446 sales@tritonimaginginc.com support@tritonimaginginc.com © 2013 TRITON This user guide is provided as a means to become familiar with TRITON’s software through an explanation of the options available for processing bathymetry data. The user interface presented in this guide is subject to change to accommodate software upgrades and revisions.
Table of Contents 1.0 Introduction...................................................................................... 1 2.0 Settings .......................................................................................... 1 2.1 General Settings .................................................................................................................................................. 1 2.2 Third Party Settings.........................................................................................
5.2.6 Re-build Using ............................................................................................................................................ 23 5.2.7 Edit GSF Using ............................................................................................................................................ 23 6.0 Enhance ......................................................................................... 24 6.1 Relief Shading ..........................................................
1.0 Introduction This document presents a sample workflow for processing bathymetry data using Triton’s Perspective software. Also covered are some of the interpretation tools available in Perspective and a brief discussion of export options. Bathymetry data used for this document were collected for the Shallow Survey 2012 common dataset in Wellington Bay, New Zealand.
NUMBER OF CORES: Below the file paths is a section titled Number of Cores for setting the number of computer processing cores (or threads) for working in Perspective. The default is 2 cores but Perspective will utilize up to 8 cores for faster performance. 2.2 Third Party Settings The tab on the far right in the Program Settings dialog is for pointing Perspective to the 3D area-based editor and the BAG file configuration data.
Select the preferred BAG file version (or leave default selection) and set the file path to the correct location as shown here: C:\BAG_StyleSheets\configdata14 (or configdata11) 3.0 Data Preparation The first step to processing data in Perspective is to prepare the raw data. 3.1 Convert Raw Data to XTF Perspective currently only reads raw data formatted as XTF files. Data collected in raw sonar formats (.all, s7k, etc.
This will open a file browser to locate the raw SVP file. Once the file is selected, the Sound Velocity Format Parsing dialog will launch as shown below: To parse the data file we first need to indicate how the values are separated (space, colon, comma, etc.). The top section of the parsing dialog is a read-out of the raw data file. This read-out shows that text and values are separated by spaces and commas in this file. Below the data read-out the Delimiters can be set to separate the values in the file.
the settings. The Decoded Header Element section in the bottom right corner of the dialog shows the information extracted from the header. The example shown on the previous page demonstrates how to extract information from the header rows. The example shown below demonstrates how to parse the data once the important header information has been defined. For this data file the only values of interest are the depth value and the corresponding sound velocity.
information extracted. Even though Temperature and other values may be present in the data file we can ignore them and only define the values of interest as shown in the Decoded Data Element section in the example. Once the important header elements have been defined and the data section is parsed, click on the OK button to return to the XML Utilities dialog.
will have a .svp_xml extension and will be used in the BathyOne processing wizard to correct the data for changes in sound velocity through the water column. 3.2.2 Tide XML Files From the File menu in the XML Utilities application, select the Open tide file option as shown right to convert raw data downloaded from a tide gauge into XML format. This will open a file browser to locate the raw tide file. Once the file is selected, the Tide Format Parsing dialog will launch as shown below.
To parse the data select any line in the top window, then set the delimiter to Comma. Set the Attribute type to Data, select the value of interest in the Parsed Field section on the left, indicate what type of value it is in the Field section and the format of the value in the Format section as shown in the example on the previous page. Once Update is clicked the Decoded Data Element window will update indicating how the value is being interpreted.
Review the range of values and axis labels and compare them with expected results before clicking Save As to create a .tide_xml file. 3.2.3 Squat XML Files From the File menu in the XML Utilities application, select the Open squat file option as shown right to convert a squat table into XML format. This will open a file browser to locate the raw tide file.
set to Data, choose the correct Field and Format for each Parsed Field, and when finished review the Decoded Data Elements to verify the data was parsed correctly before clicking the OK button. Selecting OK will close the parsing dialog and return the user to the main XML Utilities dialog shown below: Note that since squat is not dependent on the position or the date, both of these fields are grayed out.
4.0 Import 4.1 File Import To get started, the raw XTF bathymetry data files need to be imported into Perspective using the Raw Data File option from the Import menu as shown in the capture to the right. Selecting the Import/Raw Data File option will open a file browser to locate raw data files. A single file can be selected or multiple files for quickly importing multiple days of data. 4.
4.3 Navigation There are two important things that happen as the raw data is imported into Perspective. The first is the creation of cache files for each imported line. This allows the original data files to be unchanged during all the processing steps performed. The other is the extraction of the navigation data from the raw data files for display in the map view. Perspective uses a GIS-like file tree structure for managing imported data as shown to the right.
5.0 Process 5.1 BathyOne Wizard The easiest method for launching the bathymetry processing wizard is by selecting the toolbar button shown right. It is also possible to launch the processing wizard by right-clicking on the Bathymetry DTM or Bathymetry CUBE nodes in the Imagery file tree layer and selecting Create. Bathymetry processing options are divided into the following several pages in the wizard: 5.1.
A few things to note: Gridding Methods: There are two different gridding methods available, our standard DTM gridding algorithm and the CUBE (Combined Uncertainty and Bathymetric Estimator) statistical algorithm developed by Dr Brian Calder at the Center for Coastal and Ocean Mapping, University of New Hampshire. Bathy QC Layers: These extra layers load in the same file tree node as the grid file and allow the user to quickly identify areas that need further validation (see section 8.
5.1.3 Gridding of Soundings Sets the grid resolution, encoding method, and fill and smooth filters. A checkbox exists to Constrain to map view which allows the user to try different processing parameters on small areas quickly to determine what gives the best results before spending the time to process the entire data set. Shown below is an example of typical settings: A couple things to note: Bathy Encoding: Only applies to DTM grids.
5.1.4 Geometry Settings There are two options here for vessel offsets: either pole/hull mounted; or towed configurations. Vessel Mounted: Offsets can be read directly from the raw XTF data file if it was entered during acquisition. Alternatively the Create button allows the user to enter the vessel offsets and generate a vessel geometry file, and the Load button allows users to load a vessel geometry file already created. Shown right is an example of a vessel geometry file.
5.1.5 Raw Processing Several options are available on this page as shown in the example right and described below: Navigation Processing: There are 4 options for navigation processing. o Process Navigation: If the navigation was not processed from the file tree, this option should be selected and the settings dialog opened as shown right.
TPE Settings: The Total Propagated Error (TPE) for each sounding is written into the Generic Sensor Format (GSF) file when it is created. NOTE: When processing bathymetry data in Perspective, in addition to the grid layer that is the selected output of the process, a GSF file is also created for each input survey line. The GSF file contains sounding data fully corrected for navigation processing, vessel motions, and applied offsets.
UTC Timing Delay: If there is a known clock timing delay in the acquisition system it can be entered here. Attitude Correction Threshold: If the attitude data changes more than the indicated amount between pings, the ping is flagged as bad and not used. Use Attitude Edit Files: If the attitude data was manually edited with the Attitude Editor, then the saved edits can be applied with this option. Generate HTF: With this checkbox selected, HTF files will be generated.
The example on the previous page indicates all beam flagged as “Bad” will be ignored, the outside angle will be limited to 70 degrees for both port and starboard, with a depth range from 1 to 27 meters. Also the depth range indicated uses "all z-offsets" which means it is corrected to true depth and is not the depth below the transducer.
5.1.8 Tide/Squat Processing The XML files created earlier for tides and squat can be applied at this stage of the processing wizard. The example shown below is using a single tide file, however a folder of tide files can be selected and an interpolated value for the current location will be used from the three closest stations. At the base of this page of the processing wizard is where an XML squat table can be loaded if available.
5.1.9 Processing Results A few things will happen during processing of the multibeam data. 1. GSF files: As mentioned in the “Note” in section 5.1.5, a byproduct of processing in Perspective is the generation of GSF files for each imported data file. GSF files contain fully processed sounding data and are placed in a subfolder in the same directory as the grid file as shown right. 2. HTF files: The Ancillary Options page of the BathyOne wizard discussed in Section 5.1.
5.2 Other Processing Options Presented here are a few optional processing tools: 5.2.1 Navigation and Attitude Processing The BathyOne processing wizard is limited for processing navigation data since the user has no feedback to see how well the processing worked and whether it was too much or not enough. Perspective also has a new Attitude Editor that allows the user to apply simple filters to remove spikes and to manually flag points as bad.
6.0 Enhance There are three primary options for enhancing the appearance of the bathymetry grids in Perspective. These are adjustments to the Relief Shading, Color Settings and to the Histogram. 6.1 Relief Shading To open the Relief Shading dialog, right-click on the Bathymetry DTM file tree node for DTM grids (as shown to the right), or the Bathymetry CUBE file tree node for CUBE grids. Selecting this will open the window shown left.
For adjusting the color of an individual grid layer, right click on the layer name in the file tree. The example shown right is for opening the Density color settings. Selecting the Color Settings for any layer will open the window shown to the right. Apart from changing the color bar as shown in the window below, increasing the Gamma can help bring out the details in the grid. 6.2 Histogram Changing the histogram adjusts how the color map is spread across the data range.
What causes this affect is a combination of the relatively flat seafloor with some low frequency noise that stretches the data range. Adjusting the Histogram allows the user to confine the stretched color palette to a specified range of values as shown below. Note that the original Histogram stretched the color map from 13.95m to 28.5m while the revised Histogram was set to range just from 21m to 23m depth.
7.1 Swath Editor The Swath Editor in Perspective allows the user to edit the beam flags in the GSF file associated with the selected navigation line. Beam flags are used in the processing wizard to decide if the sounding will contribute to the grid cell value or not, and if so how it contributes. The Swath Editor can assign three different beam flags to a sounding: Good: use this sounding in the gridding process according to the specified encoding method.
and cleaning an entire data file from start to finish, it helps to start with a large Sweep Length (50 to 100) to cover as much area as possible per window frame, then run through the line a second time with a reduced the Sweep Length (5-20) to remove the lower level noise in the data. For settings a sounding as “designated”, using a small Sweep Length helps the user to select the correct sounding that defines the top of the structure as shown in the example shown right.
An example of the Area Editor is shown below: Area loaded into editor 3D view, colored by depth Vertical exaggeration controls Color Map Slicing controls The most commonly used toolbar buttons are described below. Allows the user to change how the soundings are colored.
Used for removing soundings within a defined polygon area Will show soundings marked as “bad” by beam suppression filters during gridding Used for restoring soundings within a defined polygon area Allows the user hide selected lines from 3D display Unloads changed beam flags on save/exit, must be selected before saving! Saves the revised beam flags to the GSF files for each line and closes A few important items to note regarding the 3D editor: In order to use the 3D editor it requires a separate install
7.3 Apply Edits to Grid In order to update the grid file with the revised beam flags, there are two options available by right-clicking on the grid layer in the file tree. 1. Rebuild Using (discussed in Section 5.2.6) 2. Edit GSF Using (discussed in Section 5.2.7) 7.4 Designated Soundings Note that for every beam flag set as “designated”, a text file will be generated during the rebuilding process in the same folder as the DTM with an .sdg extension for importing into Perspective as a Feature file.
8.0 Interpret To assist with interpretation of the bathymetry data Perspective has many added features and toolsets. This section briefly describes some of the options available. 8.1 Info Displays Cursor: The cursor tab of the info display (located above the file tree) is useful for identifying the position and depth of the cursor in the map view as shown in the example to the right. Measure: The measure toolbar button shown here allows the user to make measurements in the map view.
A few things to note: The bathy profile tool works for any grid layer including the QC layers generated during gridding (density, standard deviation, etc.). The cursor position in the profile is linked to the map view. In the images at the bottom of the previous page the cursor position in the profile is shown as a green circle (color of selected line) and this same position is displayed in the map view along the profile line.
8.3.2 DTM – Standard Deviation Layer This layer gives the standard deviation of the sounding values within each grid cell. Note that when selecting which QC layers to produce in the BathyOne Wizard the user can specify how many soundings are needed in a grid cell in order to make this calculation. Mathematically, there needs to be at least 2 values in order to calculate a standard deviation.
8.3.3 DTM – IHO Compliance There are 5 options presented in the IHO layer selection as shown to the right. The user can request the results to show how many grid cells meet IHO specifications for chosen order Special, One or Two), or the user can select ‘All’ to see what order each grid cell will pass. Selecting the last option ‘Do Not Compute’ will not generate an IHO compliance layer. Shown below are the results of the IHO compliance calculation for the 0.5m and 1m grids: 0.5m grid 1m grid Note the 0.
This equation and the values for ‘a’ and ‘b’ come from IHO Standards for Hydrographic Surveys, Special Publication No. 44. 8.3.4 CUBE Uncertainty Layer This layer is similar to the DTM standard deviation layer as it represents the amount of variation within the number of soundings used to determine the depth value. Shown below is the uncertainty layer for the CUBE depth grid at 0.5ms: 0.5m grid What the uncertainty layer represents is the total uncertainty value generated by the CUBE algorithm.
except in the center where the wreck is located. It is important that the user examines the places where multiple hypotheses were identified to verify CUBE selected the correct one. 8.4 Bathy A-B The Bathy A-B tool allows the user to subtract one bathy grid layer (DTM and CUBE grids) from another to identify differences in the depth value at each grid node.
4. Processing QC Tool: To gain a better confidence in the results from data processing it can be useful to grid the same dataset twice, once using the CUBE algorithm and again with the standard DTM algorithm, then compare the results with the A-B process. Below is an example of an A-B grid of a wreck gridded first with CUBE and then as a DTM using the ‘minimum’ depth value in each grid cell.
8.5 Backscatter and Snippet Processing (Geocoder) For backscatter and snippet processing we utilize Geocoder written by Dr. Luciano Fonseca, for the Center for Coastal and Ocean Mapping, University of New Hampshire. Currently Geocoder is a stand-alone application but work is in progress to integrate it into Perspective. To launch Geocoder, use the toolbar button shown right.
4. The last step is to select the “Assemble” option at the bottom of the Mosaic Menu. This will start the processing of the inserted lines using the selected filters. As the backscatter mosaic is created it will be drawn in the map display. Once the mosaic is generated it can be exported to a GeoTiff file by selecting “Save Tiff” in the Mosaic menu. This allows the processed backscatter to be brought into Perspective.
8.6 SeaClass Backscatter and snippet results can be classified using Perspective’s SeaClass module. Note that having bottom samples or other ground-truth information such as video, pictures or diver’s notes will increase the accuracy of the results. For more information regarding using SeaClass to classify multibeam backscatter/snippets, see the SeaClass User Guide available for download from our support website at: http://www.tritonimaginginc.com/site/content/support/downloads.htm#guides 9.
HTF files are created in the same folder as the GSF files, in a subdirectory where the grid file was written to, with the name of the subfolder matching the grid file name. 9.2 GSF For every raw data file included in a grid, a GSF (Generic Sensor Format) file is always created during the gridding process. The GSF file contains all of the bathymetry soundings from the raw data file but with their positions fully corrected for motion, SVP, and tides.
The BAG (Bathymetry Attributed Grid) file is a non-proprietary format for storing and exchanging bathymetric data and was developed by the Open Navigation Surface Working Group. 9.5 GeoTiff The gridded bathymetry data can be exported to a GeoTiff by right-clicking on the grid file in the DTM or CUBE file tree and selecting the GeoTiff export option. This will export a GeoTiff at the selected resolution of the entire bathymetry grid with no other information overlain on the image.
9.7 Printing It is possible to print what is shown in the map view to a paper printer. When selected, everything shown in the map view will be sent to the printer. This is very similar to the composite exports but the output is a paper record instead of a digital record. 9.8 Smooth Sheets (Global Mapper) In addition to the simple printing option available within Perspective, it is also possible to use the GeoTiff exports from Perspective with Global Mapper to generate smooth sheets.
10.0 Workflow Step 1 - Launch Perspective: Start application and open project or start new project. Step 2 - Check Settings: Verify maximum number of cores is selected and if desired set the initial working file path. Step 3 - Prepare Data: Launch XML Utilities to prepare sound velocity, tide and squat files for use in processing. Step 4 - Import Data: Import background data and raw data files into Perspective. Step 5 - Process Data: Use BathyOne processing wizard to generate a DTM or CUBE grid file.
