[GRASSLIST:844] Re: Planning swath bathymetry surveys

[Patton, Eric]

David, 

Very interesting! I haven't had time to test your script out, but just off
the top of my head,  could your v.split problem be solved by using v.segment
or v.to.points, perhaps? I'm just throwing this out there, I don't know what
the advantages if any are from using one of these over another. 

In general I think this is going to be a very useful addition to Grass,
especially for my work.  I'll try to add more useful feedback after I can
make some time to play around with it.

Thanks!

~ Eric.
   
-----Original Message-----
From: David Finlayson
To: Patton, Eric
Cc: Hamish; GRASSLIST at baylor.edu 
Sent: 4/23/2006 2:11 AM
Subject: Re: [GRASSLIST:773] Re: Planning swath bathymetry surveys

I tried to put together a little script to test out some ideas. Things
worked OK to a point. I ran into limits on the number of segments I
could add to a line with v.split which limits the resolution of the
resulting swath map. I also ran into problems with v.buffer which did
not buffer the lines in the way I would expect. I put together a web
page with a visual of what I mean (use the script copied below):

http://david.p.finlayson.googlepages.com/swathwidth

I would love to hear any comments on how to do this better.

---- test script ----
#!/bin/bash
# Visualize SWATH coverage from a line

LINE=survey    # A vector line
DEM=psdem2005  # An elevation raster
BEAM_MULT=3    # Beam width multiple of water depth

# Split the line into cell-sized segments (Can't do this, I get
# a out of memory error if the number of segments gets too large
EWRES=`r.info -s map=$DEM | grep ns | cut -d= -f2`
g.remove vect=temp_split
v.split input=$LINE output=temp_split length=100

# Now remove duplicate categories (for each segment) and
# renumber consecutively
g.remove vect=temp_split2
v.category input=temp_split output=temp_split2 option=del
g.remove vect=temp_split3
v.category input=temp_split2 output=temp_split3 option=add

# Attribute each line with an elevation and upload to the
# attribute table
g.remove vect=temp_drape
v.drape input=temp_split3 type=line rast=$DEM output=temp_drape

v.db.addtable temp_drape col="x double, y double, z double" layer=1
v.to.db map=temp_drape type=line option=start col=x,y,z layer=1

# Assign z value to segments from dem. Then calculate the width
# of the beam as a function of water depth and store this in a
# second (layer 2) attribute table
echo "DROP TABLE temp_drape2" | db.execute
echo "create table temp_drape2 as select cat, x, y, z, -1 * $BEAM_MULT
* z as width from temp_drape" | db.execute
echo "update temp_drape2 set width = 0 where width < 0" | db.execute
v.db.connect -o map=temp_drape table=temp_drape2 layer=1

# Buffer the line segments based on the width attribute (This doesn't
# do what I expected)
g.remove vect=temp_buff
v.buffer input=temp_drape output=temp_buff type=line layer=1
bufcol=width tolerance=0.01

# Convert to buffered vector to a raster
g.remove rast=survey_buff
v.to.rast input=temp_buff output=survey_buff use=val value=1

---- end script ----


On 4/20/06, Patton, Eric <epatton at nrcan.gc.ca> wrote:
> David,
>
> What water depths will you be working at? I ask because you can
usually plan
> parallel lines in deeper water where you don't have to contend with
islands,
> shoals, fishing gear, etc. We use Regulus software from ICAN as our
nav
> package for swath surveys, but all it really does is plot parallel
lines of
> a given length and angle orientation, (i.e. v.parallel, v.digit). For
> non-parallel survey grids, we really just digitize arbitrary survey
tracks.
>
> I'm not sure if the MB-System has a survey grid making tool, maybe
worth a
> check:
> http://www.ldeo.columbia.edu/res/pi/MB-System/
>
> ~ Eric.
>
>
>
>
> -----Original Message-----
> From: owner-GRASSLIST at baylor.edu
> To: David Finlayson
> Cc: GRASSLIST at baylor.edu
> Sent: 4/19/2006 11:48 PM
> Subject: [GRASSLIST:773] Re: Planning swath bathymetry surveys
>
> > Has anyone built a tool to assist in planning SWATH bathymetry
surveys
> > in GRASS? Alternatively, do you know of a tool that would take
> > existing bathymetry as input and help me plan survey lines?
>
> r.transect -g, r.profile -g
> and make vector lines from result, then v.buffer?
> That way might be fairly labor intensive without a script.
> just use v.digit or QGIS digitization of lines over a DEM backdrop?
>
> how much will depth vary? (as beam width & space between tracks will
> increase with depth)
>
> "v.mkgrid angle=" might be quite useful
>
> Simrad setup or similar? digital out?
>
> For old paper Sidescan Sonar recorders + GPS track the new thin plate
> spline warping in gdalwarp has given me much better results than with
> Caris GIS or ERDAS. A few bumps along the way but in the end a pretty
> smooth process.
>
> Someone made a good free (beer) data viewer for swath data.. can't
> remember the name now :/ I'll rereply if it comes to me.
>
> Ocean Data View isn't really what you're after, but maybe useful:
>   http://odv.awi-bremerhaven.de/
>
> Also check out Bob's Tekmap website. http://www.tekmap.ns.ca/
>
>
> Hamish
>
>


--
David Finlayson