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| Subject: | Re: [gislist] GIS Survey Question |
| Date: |
01/26/2004 09:50:00 AM |
| From: |
Jon Coleman |
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Layne,
The comment re terrain conditions and breaklines is largely correct,
however, you must also consider the type of vegetation cover in order to
assess what the likely penetration ratio of the LiDAR system will be. With
LiDAR the accuracy of the data is largely a function of oversampling,
typical RMSE of LiDAR points is in the order of 10-15 cm, however, the error
in a well executed survey with a well calibrated system is as a result of
random GPS and ranging errors. With sufficient redundant sampling you are
able to a large extent overcome these. Typically in our experience, in
order to achieve 6 " type contour accuracy requires samples in excess of 6
points per sq meter.
Regards,
Jon Coleman
----- Original Message -----
From: "Layne Seely" <LSEELY@cpyi.com>
To: <JBYRON@ci.st-augustine.fl.us>: <ARCVIEW-L@ESRI.COM>: <esri-l@ESRI.COM>:
<gislist@lists.geocomm.com>
Sent: Monday, January 26, 2004 9:30 AM
Subject: Re: [gislist] GIS Survey Question
hey Jonathan:
The site is a small island that we do not expect to have much in the way or
relief. I understand that I can take fewer postings on primarily level
ground and concentrate postings around/within areas of relief. In addition
to getting an idea of postings placement, I'm trying to figure out how long
this will take.
Thanks for the reply.
Layne
>>> "JONATHAN BYRON" <JBYRON@ci.st-augustine.fl.us> 01/26/04 09:21AM >>>
Not sure if there is a rule of thumb that can be used on all terrains with
mathematical precision. If the area is very flat / homogenous (Everglades,
playa lake regions, etc) , then points could be widely spaced and the
accuracy would be good. If the surface is complicated with high relief (many
steep scarps or cliffs), even "closely" spaced points would lead to contours
that don't fit the ground truth very closely. Any idea what the fractal
dimension of your Yucatan surface is? Disclaimer: I am not a surveyor.
Jonathan
>>> "Layne Seely" <LSEELY@cpyi.com> 01/26/04 09:28AM >>>
hey Group:
I have been tasked with planning and performing a land survey to generate
contours for a project. We will be using the Leica SR530 to collect point
data to support the creation of 6" contours. The site may have as much as
10' total elevation above sea level (it's near the Yucatan peninsula :))
What I need to know is how closely I need to plan my points to warrant 6"
contours. From what I know of Lidar, you plan 2.5m postings to generate 2'
contours. If my math is correct, I will need to collect a posting every 2'.
Is this basically correct?
Mr. Layne Seely
GIS Analyst
CHIANG, PATEL & YERBY, INC.
1820 Regal Row, Suite 200
Dallas, Texas 75235
214.640.1736 (Direct)
214.638.3723 (Fax)
LSeely@cpyi.com
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