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| GeoCommunity Mailing List |
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| Subject: | Re: [gislist] Lake Bottom TINS |
| Date: |
09/29/2003 11:40:00 PM |
| From: |
viktoras |
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|
It's hard to tell what is "the best". We do it this way:=0D
=0D
1) using a combination of GPS/echosounder to read parallel transect lines
between the opposite sides of a lake. Distance between 2 transects for a =
3x4
km lake is constantly around 100 m for the whole area. Sure, it can be le=
ss
if higher precision is needed or if a lake is smaller or money and field
work time resources are high. But for the TINs it should be more or less
constant. However if rain starts or wind direction changes during these
surveys, then they are very likely to cause an error because of water lev=
el
fluctuations...=0D
We use Windmill software for "live recording".=0D
I would recommend to follow only parallel transect lines and avoid any
crossing especially if sampling takes several days as it may introduce mo=
re
artifacts into data.=0D
=0D
2) All bad readings and evident errors have to be removed (e.g. 20 m
reading for a max 5 m depth lake, etc...). This happens quite frequently =
if
boat speed is too high or there are waves on a surface or head of an
echosounder is too close to the surface and one gets bubbles below it,
sometimes dense bottom vegetation can cause odd readings... =0D
Another issue is sensitivity of GPS and precision of GPS readings. Someti=
mes
if precision is questionable one can have several different depth readin=
gs
for the same possition. I use a small script to calculate average depths =
for
identical coordinates in such cases...=0D
Then data needs to be resampled to get more or less uniform distances amo=
ng
all points for interpolation. I use a small script to capture each tenth
(or whatever specified, depends on GPS/echosounder/software settings) poi=
nt
from transect lines. Then an offset of the echosounder's head should be
compensated. Once you eventually have a network of points for the whole a=
rea
(and include coastal line as zeros) continue with the interpolation... =0D
=0D
That's it... Hope it helps.=0D
=0D
Best regards=0D
Viktoras=0D
=0D
=0D
=0D
=0D
=0D
=0D
=0D
=0D
-------Original Message-------=0D
=0D
From: Theresa.A.Dawson@Lrh01.usace.army.mil=0D
Date: 2003 m. rugs?jis 29 d. 07:43:31=0D
To: gislist@lists.geocomm.com=0D
Subject: [gislist] Lake Bottom TINS=0D
=0D
I have a philosophical question. =0D
=0D
=0D
=0D
I get lake and river bottom survey line data from a combination=0D
fathometer/GPS unit. The lines run 400 to 500 feet apart with a somewhat=0D
closer spacing around bends. Now people want TINS from this data. I know=0D
this isn't the best set up. So my questions are:=0D
=0D
=0D
=0D
1) What is the best way to get data for a lake bottom TIN=0D
=0D
And=0D
=0D
2) How can I make the best TIN given the survey line data I've got.=0D
=0D
=0D
=0D
Terry Dawson=0D
=0D
US Army Corps of Engineers, Huntington District=0D
=0D
_______________________________________________=0D
gislist mailing list=0D
gislist@lists.geocomm.com=0D
http://lists.geocomm.com/mailman/listinfo/gislist=0D
=0D
_________________________________=0D
This list is brought to you by=0D
The GeoCommunity=0D
http://www.geocomm.com/=0D
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