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Semivariogram model values and exporting

SThompson

Hello
I was wondering what the different parts of the model function on the modelled semivariogram graph refer to.
e.g.,Model : 861.57*Nugget+8817.6*Tetraspherical(150000)

what is the 861.57? what is the 8817.6?

I was also wondering what the different variogram export tables are. Obviously distance is distance along the x axis, what is "value"? is that the semivariance values?

Thank you!

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anandkakarla

From the graphic it appears that your data are in a projected coordinate system and the unit of measure is meters.

Did you assign a spatial reference to the data from the Excel file, in other words;
- right click the input point feature class and under the Source tab, do you have a projected coordinate system?

What is the extent of your input data, in other words, how many meters by how many meters?

-Steve

Sir,
the i guess lat and long cordinates refer to geodetic wgs84.i hope i am right ?! but maintaining the gcs of wgs84 cordinate system gives me variogram in degres. i attached the corresponding variogram....and this is its data source
Geographic Coordinate System: GCS_WGS_1984
Datum: D_WGS_1984
Prime Meridian: Greenwich
Angular Unit: Degreethis data is from whole california ...max distance is 2000 km
Data Type: XY Event Source
Location: C:\Users\IIT\Desktop\frgis2.xls
Table: Sheet1$
X Field: F3
Y Field: F2
Z Field: F4
Has Object-ID Field: No
i changed the projection to the some projection system to have the xaxis in meters. the values are the same, the plot is the same ,following is the data source for my previous attachment
Projected Coordinate System: US_National_Atlas_Equal_Area
Projection: Lambert_Azimuthal_Equal_Area
False_Easting: 0.00000000
False_Northing: 0.00000000
Central_Meridian: -100.00000000
Latitude_Of_Origin: 45.00000000
Linear Unit: Meter

Geographic Coordinate System: GCS_Sphere_Clarke_1866_Authalic
Datum: D_Sphere_Clarke_1866_Authalic
Prime Meridian: Greenwich
Angular Unit: Degree
this is the data source........
Data Type: XY Event Source
Location: C:\Users\IIT\Desktop\frgis2.xls
Table: Sheet1$
X Field: F3
Y Field: F2
Z Field: F4
Has Object-ID Field: No

newcapaecgis.PNG

SteveLynch

From the graphic it appears that your data are in a projected coordinate system and the unit of measure is meters.

Did you assign a spatial reference to the data from the Excel file, in other words;
- right click the input point feature class and under the Source tab, do you have a projected coordinate system?

What is the extent of your input data, in other words, how many meters by how many meters?

-Steve

anandkakarla

Sir,
I am new to this Arc GIS. i was tring to krige the dataset i have . I have 100 samples with location(lat,long,elev) and its sample value(california) in an excel sheet. i exported the values and used Geostatistical analyst to obain the variogram plot. The plot x axis is supposed to be in ''h^10-5''.But it is only in ''h''. i attached the variogram plot. please some one help me how to get the correct x axis

Capture22.PNG

EKrause

When you manually set a lag size and number of lags, the software will never use a Major Range that is larger than the lag size multiplied by the number of lags (unless you manually specify a Major Range). So, if the software is using (lag size x number of lags) for the Major Range, this indicates that the optimal Major Range is larger than the product of lag size and number of lags. This means that your lag size is likely too small (or the number of lags is too low).

If you use the "Optimize Model" button (available in ArcGIS 10), the software will calculate the Major Range (among other parameters) in order to minimize the Root-Mean-Square error (RMS). Using this button is our recommendation for finding the best semivariogram parameters, including Major Range.

SThompson

Hi again, I'm not quite understanding the "major range."

When I var the number of lags and lag size to values that I've chose, the major range I am getting is simply the product of lag size * number of lags. Is this indicative that I need to increase my lag size or number of lags?

SThompson

Thank you for that information, Eric

SThompson

Thanks Eric!

EKrause

Model : 861.57*Nugget+8817.6*Tetraspherical(150000)

861.57 = Nugget
8817.6 = Partial Sill
150000 = Major Range

In the Geostatistical Wizard's variography page, you can see that values correspond to the parameters on the right.

There are various export options on the variography page in the Geostatistical Wizard. You can output the red dots (binned values), the blue crosses (averaged values), and averaged values using geometrical intervals (you don't see these in the semivariogram graphic, but they are the values that are used in our weighted least-squares algorithm to fit semivariogram parameters). The main reason to export is that you can graph the semivariogram in another program like Excel, where you have more control over the graphic (like changing colors, labels of axes, etc).

You can also export the Semivariogram/Covariance map, either as a raster of weights or a raster of values (where the value is either the semivariance or the covariance, depending on whether "Variable" is set to Semivariogram or Covariance).

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