under discussion. Meanwhile,
more comments and suggestions are welcome.
Best regards,
Chaosheng Zhang
- Original Message -
From: "Chaosheng Zhang" <[EMAIL PROTECTED]>
To:
Sent: Thursday, May 25, 2006 9:12 AM
Subject: Effects of spatial autocorrelation on descriptive st
ue of a
"block kriging" (perhaps on the centroid?) be regarded as the estimated
mean value of a study area?
Cheers,
Chaosheng
- Original Message -
From:
Isobel Clark
To: Chaosheng Zhang
Cc: ai-geostats@jrc.it
Sent: Friday, May 26, 2006 7:19
eng
- Original Message -
From: Isobel Clark
To: Chaosheng Zhang
Cc: ai-geostats@jrc.it
Sent: Thursday, May 25, 2006 3:59 PM
Subject: AI-GEOSTATS: Re: Effects of spatial autocorrelation on descriptive
statistics
Chaosheng
Some thoughts in response to your questions:
1: "Spatially corr
on for the
calculation of mean";
2. "In the presence of spatially correlated data, would a dispersion
variance . be the proper calculation for the measure of variance?"
Best regards,
Chaosheng Zhang
------
Dr. Chaosheng Zhang
Lecturer in GIS
Department of Geography
National Univ
Dear all,
I have the same concerns with ArcGIS Geostatistical Analyst Extension
(v.9.1). I would use a traditional geostatistics software package
to fit the variogram models in a very traditional way, and input the parameters
to ArcGIS for kriging. It seems that ArcGIS has its own
Hi Dave,
My concern is that the 25 locations may not be
enough to capture the spatial structure of the parameter (which climatic data?)
across the UK. As discussed earlier in this list, you need to perform analyses
on spatial correlation. If your data is lack of spatial (auto)correl
t? (2) Has anybody
used the global standard errors (in geostatistics) to replace the mean
standard errors (in classical statistics) in t-test?
Cheers,
Chaosheng
- Original Message -
From: "Isobel Clark" <[EMAIL PROTECTED]>
To: "Chaosheng Zhang" <[EMAIL PROTEC
Isobel,
Good idea, and that's a step forward. Any references or is it still an idea?
Cheers,
Chaosheng
- Original Message -
From: "Isobel Clark" <[EMAIL PROTECTED]>
To: "AI Geostats mailing list" <[EMAIL PROTECTED]>
Sent: Monday, December 06, 2004 1:07 PM
Subject: Re: [ai-geostats] F a
Title: RE: [ai-geostats] F and T-test for samples drawn from the same p
Besides the discussions on the theory, I think
we need a practical solution for Colin Badenhorst's initial problem (This is not
his problem only). He wants to compare two sets of spatial data with several
thousand s
Dear all,
I'm wondering if sample size (number of samples, n)
is playing a role here.
Since Colin is using Excel to analyse several
thousand samples, I have checked the functions of t-tests in Excel. In the Data
Analysis Tools help, a function is provided for "t-Test: Two-Sample
Hi all,
The interesting story given by Tim
Glover is a good example of "spatial outliers". The dumptruck loads of
polluted soils are too different from the neighbourhood, and thus they should be
regarded as spatial outliers. When one cannot get a decent variogram after
trying all
-
Original Message - From: "Isobel Clark"
<[EMAIL PROTECTED]>To: "Chaosheng Zhang"
<[EMAIL PROTECTED]>Cc: <[EMAIL PROTECTED]>Sent:
Tuesday, March 09, 2004 11:34 PMSubject: AI-GEOSTATS: Re: mixtures of
populations> AH me, the English language
Dear
Isobel and all,
This is an interesting topic. I
appreciate the ideas of the software "MIX", but have not tried it yet. If
somebody finds it "really" useful, I may have a try. My main concern is that one
needs to define subpopulations prior to separate mixed populations, b
Following Pierre and Isobel's replies, an
alternative way is to use a GIS. You may do the kriging (or another method)
in the ordinary way, and then overlay your interpolated surface with your
polygons. Each of the irregular polygons should cover several (or tens or
hundreds or more,
ot;zij" <[EMAIL PROTECTED]>
To: "ai-geostats" <[EMAIL PROTECTED]>; "Chaosheng
Zhang" <[EMAIL PROTECTED]>
Sent: Monday, August 11, 2003 7:13 PM
Subject: RE: AI-GEOSTATS: Summary: Large sample
size and normal distribution
> Hi,> > I'm no
Dear All,One
week ago I posted a question about large n and normal distritbuion, and have got
several good replies from Isobel Clark, Ned Levine, Ruben Roa Ureta, Thies Dose,
Chris Hlavka, Donald Myers and Jeffrey Blume. Jeffrey is perhaps not in the
list, but I assume he has no objections if
that the
large sample size is also making trouble.
I am looking for references on this topic. Any references or comments are
welcome.
Cheers,
Chaosheng
------
Dr. Chaosheng Zhang
Lecturer in GIS
Department of Geography
National Unive
pling"
to reduce nugget effect. I am dubious about this practice. Since
variogram is a global paramter, areas with clustered samples may be
over-represented. Any comments?
Cheers,
Chaosheng
=
Dr. Chaosheng Zhang
Lecturer in GIS
Dep
gards,
Chaosheng
=
Dr. Chaosheng Zhang
Lecturer in GIS
Department of Geography
National University of Ireland
Galway
IRELAND
Tel: +353-91-524411 ext. 2375
Fax: +353-91-525700
Email: [EMAIL PROTECTED]
[EMAIL PROTECTED]
Web: http://www.nuigalway.ie/geog
autocorrelation, Spatial outlier, etc.?
Geostatistics:
Variogram, Kriging, Simulation, etc.?
Regards,
Chaosheng Zhang
-
Short answer is yes to everything.
middle length answer is that Normality is not required
for anything except where it is a basic assumpti
Isobel,
Thanks for the reply. I feel this problem deserves more discussion.
I have found the message from: Gregoire Dubois, Date: Mon Mar 5, 2001,
Subject: AI-GEOSTATS: SUMMARY: Nscore transform & kriging of log normal
data sets (The original author couldn't be found, and s/he should be in the
tial statistics:
Spatial autocorrelation, Spatial outlier, etc.?
Geostatistics:
Variogram, Kriging, Simulation, etc.?
Regards,
Chaosheng Zhang
==
Dr. Chaosheng Zhang
Lecturer in GIS
Department of Geography
National University of Ireland, Galw
.
Regards,
Chaosheng Zhang
Original question:
Dear list,
First, I would like to say thank you to Gregoire for keeping this list
alive.
I'm trying to do "risk assessment", and I have some questions about risk
assessment with Gaussian Simulati
e pixel is increased by adding this
kind of errors.
I am not clear how to calculate the total standard deviation of the two
sources, is it:
Total standard deviation =
SQRT (Kriging Variance + SQUARE (Sampling Errors) ) ?
Any ideas and comments on this method?
Chaosheng
erts" <[EMAIL PROTECTED]>
To: "Chaosheng Zhang" <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>; "Dave McGrath" <[EMAIL PROTECTED]>
Sent: Saturday, April 27, 2002 4:53 PM
Subject: Re: AI-GEOSTATS: Risk Assessment with Gaussian Simulation?
> Hello,
;?
Following the above question, I have a
problem in doing PCLASS. I cannot input the file name of Kriging variance to the
field of "Value error" of the documentation file. It seems that this
field only accepts a "value", not an "
regarded as a spatial outlier).
Good luck.
Chaosheng Zhang
=
Dr. Chaosheng Zhang
Lecturer in GIS
Department of Geography
National University of Ireland
Galway
IRELAND
Tel: +353-91-524411 ext. 2375
Fax: +353-91-525700
Email: [EMAIL PROTECTED
ran's I
(2) Local Moran's I
(3) Test for their significance level
(4) Spatial Correlogram
(5) Weighting function Wij which is suitable for polygon and point data
Cheers,
Chaosheng Zhang
===
Dr. Chaosheng Zhang
Lecturer in GIS
Department of Geography
Na
comments and suggestions are quite helpful. As mentioned in several
replies, this problem is also related to sampling design, Kriging grid
system design, and spatial variation.
Please find following the original question and the replies.
Cheers,
Chaosheng Zhang
l the extreme
values with 99% or 98% percentiles. But I'm not sure if it is appropriate to
do so.
Cheers,
Chaosheng Zhang
- Original Message -----
From: "Marcel Vallée" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>; "Chaosheng Zhang" <[EMAIL PROTECT
can be smoothed. I don't think this is the realistic situation
in the field.
Well, I am still not very confident what the best way should be ... I know
the worst way is to discard these "outlying" values, and the second worst
way is to use non-parametric methods.
Cheers,
Chaosheng
values which account for less than 2% of the total sample
number.
Any suggestions?
Cheers,
Chaosheng Zhang
===Dr. Chaosheng ZhangDepartment of
GeographyNational University of IrelandGalwayIRELANDTel:
+353-91-524411 ext. 2375Fax: +353-91-525700Email:
[EMAIL
Please find the following advertisement for three GIS
positions at National University of Ireland, Galway. Please reply to the
addresses according to the advertisement, not to the sender.
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