The 1 km data were generated by downloading 30-arc-second data from a Web site several years ago (the link is probably preserved in my Favorites folder on one or another computer but will probably not be used again as superior data are now available). The data were organized in a matrix with the location of the northwest corner specified. I wrote a Visual Basic program in Excel (Dr. Brown teaches this class when there is sufficient demand) to turn the matrix into (X,Y,Z) values and then used another spreadsheet I developed to convert latitude and longitude into UTM values. Then I used Surfer to calculate values at nodes of a 1 km UTM grid and then exported the Surfer grid as an ASCII file and used a Visual Basic program to convert from Surfer grid format to (X,Y,Z). Added to this are a hundred or so elevations from data points collected as part of a gravity survey by a consultant, gravity data I analyzed and interpreted.
Of course, I don’t want to have to repeat this process so I saved copies of this data set as an Access database in several locations, including an archive CD-ROM.
The 3-arc-second was much simpler. Shuttle radar elevation data are available for most of the earth’s land surface. I used the seamless data download Web site to select this geographical area and unzipped the file after download. I opened the file in Global Mapper 7.2, projected the data in UTM (NAD83 – I think) and then used a GM 7.2 utility to export as XYZ ASCII file with meters as distance units.