May 19, 2000

Back to Main G274 TA Page A sample final project

Objective: Generate a DEM for the Pacific Northwest using elevations from Agrimet Climate Stations

Data: Obtained from Agrimet web site. Actual data in html tabular format here.

Getting Data into Excel (yes, Excel!):

• Save the data location page to the desktop of my local machine as agri.html
• Start Excel. Choose File-open, agri.html
• Select just the elev, lat, and lon columns in the table (with column headers), hit Ctrl-C to copy.
• Insert a new worksheet. Click on the paste special button, choose Values.
• Now you have just the data you need, but it's not in the right format.

Converting dms to km:

Copy the latitude column over to column H (or thereabouts)

Break the latitude out into 3 columns:

Select the H column

In the Data menu, choose 'text to columns'

Click the delimited button and hit 'next'

Check the space box and hit 'finish'

Calculate decimal degrees in column K (or thereabouts)

Click in cell K2

Enter the formula: =(((J2/60)+I2)/60)+H2

Copy the formula through row 55

Repeat for the longitude

Copy and paste special as value the dd columns to a new worksheet (columns A and B)

Convert to your favorite projection ;)

Find central meridian and parallel

Click in cell A57

Type =AVERAGE(A2:A55)

Copy this to B57 for the average parallel

In cell C1 type Earth's radius (km):

In cell C2 type 6378.166

Put x coords in Cassini projection in Column E

In cell E1 type x

Click in Cell E2

Type: =$C$2*((A2-$A$57)*PI()/180)

Copy this through cell E57

Put y coords in Cassini projection in Column F

In cell F1 type y

Click in cell F2

Type: =$C$2*((B3-$B$57)*PI()/180)

Copy this through cell F57

Save the Cassini coordinates and elevations in a nice pristine new spreadsheet

• Copy columns E2 and F2 to columns A and B in a new spreadsheet ( (use paste special - Values!)
• Go find the column with elevations that you copied from the Agrimet table. Copy it to the new spreadsheet.
• Save the new spreadsheet as agri.xls
• This is my agri.xls if you didn't want to do the work... ;)

Get the data from the spreadsheet into Splus
 

• Make sure the column headers are single words - ie. x, y and elev
• Save agri.xls as a tab-delineated text file, or download it here: agxl.txt
• Open notebook or another text editor and start typing a script (or copy from the linked text file)

• The first section brings the data in using read.table. In Splus type help(read.table) to learn more about this powerful command.

Surface Analysis on the Agrimet Data
The remainder of agri.ssc demonstrates how to generate images, trend surfaces, variograms, and kriging models for the elevation.
 

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