A variety of software packages will plot, contour, and analyze x,y,z data. We have used Surface 3 in the past, a Mac based, freeware program from the Kansas Geological Survey. Enough advantages have accumulated that noe we use Surfer, a PC commercial product, which is available in the DSC computer lab. The similarities between the two are significant, but Surfer has more options. In both cases you can learn enough in an hour to produce usable products, which is the purpose of this lab.
You can think of the process of producing a contour map with the computer as 5 fold:
Remember the help option the documentation is decent for this program.
Getting the data in:
There a several ways to do this, and we will explore 2. The easiest
is to have your data in an Excel spreadsheet as three columns
of x, y and z data. The first row can be data labels (e.g. easting,
northing and elevation). You can open this directly from the gridding
option (see below). Keep it simple to start with, and only have
your data on the sheet. If your data is originally in latitude
and longitude you need to convert it to UTM in order to have map
without signficant distortion. You
can use this UTM-lat.long transformation module. Use NAD 83
for you geodetic datum when you make the conversions. For the
many parts of the world you can download Exel calculators that
will do the transformation for that particular part of the world.
The second option is to open a tabular data sheet within Surfer.
To do this Select File/New. Choose the worksheet option. Enter
your data. You will need to save it as a file before you can access
it from the Grid option. You can copy and paste from Excel. Once
you've entered and saved your data then you can close this window
to get to the plotting window.
Gridding the data:
Select the Grid/Data option. Find the file you want to grid, and
select it. Note that once again, you must save the data as a grid
file that you will access from the Map option. When working on
one project you will likely have a minimum of 3 files: a data
file, a grid file, and a plot file. Get used
to it. ArcGIS, a software package we will explore later, produces
a plethora of files, and for large projects file management is
an important issue. Note that in the windows in Surfer that open
you have a variety of gridding options. The kriging option is
the default one, although in this exercise you will look at some
of the others. As you explore the different gridding options you
will see that the gridding option you use is important. Your reading,
and lecture notes should give more insight into the different
gridding options. Note that a report is produced when you grid
the data. Familiarize yourself with the information provided in
the report.
Contouring the data:
Once you have a grid file you can contour it, or create wire-frame
models, or a variety of other outputs. For this exercise you should
try all except the base map option and the vector option. Note
the Map/3Dview option. Once you have created a map and selected
(click on it so the 'handles' are evident), one can then change
the perspective with this option. Note that this works on other
'maps' than the wireframe.
Making the product 'pretty':
In the interest of time we will not focus on this aspect in this
lab. Nonetheless, it is important to make your products user friendly
and informative. Obviously, the map should be well labeled so
that the reader knows what they are looking at. In addition, Surfer
allows you to color and customize your maps in a great variety
of ways. If you have the time and interest you can explore some
of these options.
One other cautionary note. With such high powered software one
can make the map look better than it should, perhaps giving the
impression of false precision and/or accuracy. You should take
pains to let the reader know what data the modeled surface is
based on, and how that data has been processed. This is where
the Post map option is important.
Getting the product in the right format:
If you want to include the map or plot in a word, document, or
web site, or in some other software environment you may need to
export as a file. Surfer will export images as AutocadDXF files,
bitmaps, tiffs, jpegs and ESRI shapefiles. The Export option is
under the file menu. You don't need to do this for this exercise.
Your assignment this week is to find some x,y,z data of geologic significance and plot it. Many other possibilities exist. Remember that you are modeling some sort of presumed spatially continuous distribution of data and point phenomena such as earthquake will not work. Note that if your data comes with latitude, longitude position and you plot it as such, there will be significant distortion. Your best bet is to transform it into UTM coordinates of easting and northing. There is a UTM calculator on the web that can do the transformation nicely, but the problem is you have to enter each data point one by one. There are different UTM zones, defined by different starting points, and you need to make sure all your data falls in the same UTM zone. Remember that a degree latitude is more constant in length, but lengths across longitude vary extremely as a function of latitude position and this distortion is especially pronounced in polar regions. Best to transform to UTM. Some databases will allow you to choose the type of location output. Try to get at least 40-50 points to plot.
Your final project should consist of:
a) a copy of at least part of your data, along with a description
of the data and the data source.
b) a Post map showing the labeled data points.
c) a contour map where the kriging option was used (labeled as
such).
d) 2 contour maps where another gridding option was used. You
will need to save yet other grid files.
e) a paragraph describing how the resulting contour maps differ
and why. Indicate which gridding routine you think produces the
best results.
f) a wireframe diagram of the contour map you think most representative.
g) a shaded relief map of the same contour map.
h) a discussion of the scientific significance of your map.
Don't hesitate if you have any questions. Cheers!