So far we have unraveled the raw data and did some QC-ing in swathed. In the previous part we already made a temporary dtm to aid during the cleaning process. In this chapter the final steps to making a bathy dtm or backscatter image are described.
The chart production process is different for bathymetry and backscatter. It even requires some different commands for Resonor Simrad data.

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Bathymetry

You might have noticed while making your temporary dtm that it reaches a large size as your looking at a big dataset. In such a case it is better to use a larger pixel size (as it is only used for cleaning interpretation this may not harm to much), or decide to partition the dataset in smaller areas. The latter is more feasible cause the file size is limited though you' ll keep good grid resolution (e.g. 1x1m). This is done by making so called Box headers.

My approach is to first make a mapsheet of the complete area and create the box headers (=smaller areas). I decide to use the navigation track to get a feeling of the area's of interest, so the pixel size of the mapsheet won't dominate and subsequently the file size wont exceed. (I assume you already have the boundaries of the complete data set, other wise:

getBounds merged/sub_dir/*merged
)

I) make_blank

make_blank overview -boundsof ../merged/sub_dir/*merged

The program asks for the data type, either floating point or 8bit. A floating point data type is used for bathymetry. A 8bit number ranges from 0 to 255 (2⁸=256) and are used to represent the grey level values for backscatter data.
For our case choose floating point array (2).
Use a fair big pixel size like 25 or so.

II) Box.header Now select your box headers and view the navigation track:

jview overview.blank -pickrot -navlook ../decnav/sub_dir/*decnav

-pickrot
pick and rotate a boxheader

-navlook
look at the navigation track and direct to the path of the decnav files

To enable the pickrot function you first need to have a subarea opened, zo just zoom in somewhere. With the right mouse button you can place the box. Scale it with the left and right arrow keys and rotate it with '+' and '-'. Choose a new box with 'n', exit when your done.

If you look at the list now you'll see it created several Box.headers:

Box.header0 Box.header1 etc etc..

Create dtm's of each area in the box header. We do this with the make_blank, tor4, weigh_grid and addSUN functions.

make_blank dtm_name -area Box.headerx

-area
with -area your using the boundaries, ellipsoid and projection of the specified box header. You may want to take notes which box headers belong to which area, but you can also rename them if you wish.

If you want to change a projection, ellipsoid or whatever, use the edhead command (edit header):

edhead -show Box.headerx
The -show option displays the parameters of the Box.header. Without specifying the -show option you'll reach a menu that enables you to modify the parameters. You can also use edhead for r4-, sun and 8bit files.

III)r4 weigh_grid addSUN Create the r4:

tor4 dtm_name

....and fill it with bathy data:

weigh_grid -beamwidth x.x -custom_weight a_beam_weightfile dtm_name ../merged/sub_dir/*merged

recall:

-beamwidth
takes the beam dimensions into account

-custom_weight
use a specified weight file (of the beams! NOT the weight file generated by the tor4 function.)

Get a sun illuminated to:

addSUN dtm_name

This default uses 315 degrees azimuth, you can change it with the -azi xxx option.
Look at the results so far:

jview dtm_name.r4 dtm_name.sun_315

To reach a better contrast stretch the color range over the color bar. Hit 'h' for histogram while pointing with the mouse on the mapsheet. You'll notice the histogram in the color bar, stretch it with the left an right mouse buttons. Make notes of the greylevel values (only for sun image). Do the addSUN again and provide the greylevel range:

addSUN -range xxx xxx dtm_name

IV)mix_ci Combine the colors with the sun illumination with mix_ci (color intensity). The mix_ci command needs 8bit images, a sun-file is an 8 bit (values ranging between 0-255 remember) but the r4 has floating point values. Thus we need to convert those to a 8bit image:

r4to8bit dtm_name

It creates dtm_name.8bit. NOTE, use the command without the .r4 extension!

mix_ci -mask dtm_name.sun_315 -ignore 255 -c dtm_name.8bit -i dtm_name.sun_315 -ppm -m output_name

-mask
provide the sun file as mask. All data outside the mask gets value 0 (=white).

-ignore 255
gaps in the data will be filled black

-c dtm_name.8bit
the .8bit dtm file provides the colors

-i dtm_name.sun_315
the .sun file provides intensity values

-ppm
output it as a .ppm-file

-m
outputname

View the result with:

xv outputname.ppm

V)adding contours

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Backscatter

UNDERCONSTRUCTION!!!!

Reson

Simrad

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back 2) Gridding and cleaning

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