Surfer 8 Training Course

Surfer 8 Training Course

Part two

By Geologist \ Ragab Elbanna

Egyptian mineral resources

Mineral exploration

E.Mail:

Cell Phone: 012 1822560

I. Introduction to Surfer

What Surfer can do

Surfer 8 is a software package which transforms XYZ datato create contour maps, 3D surface maps, 3D wireframe maps, shaded relief maps, rainbow color"image" maps, post maps, classed post maps, vector maps, and base maps. It can calculate crosssections, areas, and volumes.

Types of files that can be imported

• Data file formats: XLS, DAT, SLK, Lotus and Symphony W??, CSV, ASCII, BNA, and BLN

• Grid file formats: ASCII GRD, binary GRD, USGS DEM, GTOPO30, SDTS DEM, and DTED

• Base maps: EMF, E00, GSI, DXF, DLG, LGO, LGS, GSB, BNA, BLN, PLT, CLP, WMF, SHP,

MIF, CMP, JPG, PNG, TIF, TGA, PCX, DCX, WPG, PCT GIF, and USGS SDTS TVP

Types of files that can be exported

• Vector formats with map coordinates: BLN, GSB, GSI, DXF, SHP, BNA, and MIF

• Vector formats with XYZ coordinates (contours only): DXF

• Bitmap formats: BMP, TIF, TGA, PCX, GIF, WPG, PCX, DCX, JPG, PICT, and PNG

• Formats that support both bitmap and vector data: CGM, CLP, WMF, EMF

• EPS: Create an encapsulated PostScript file by installing a PostScript printer, connecting it to"FILE:", and printing to that driver.

• PDF: Create an Adobe PDF file by installing the full version of Adobe Acrobat (or a free versionsuch as CutePDF) and printing to the Acrobat Distiller or PDF Writer drivers.

• Grid formats: ASCII XYZ DAT, ASCII GRD, Binary GRD, Surfer 7 Binary GRD

• Data File formats: XLS, SLK, CSV, TXT, DAT, BNA, and BLN

Setting preferences

There are two levels of preferences that can beset. The easiest ones are located in the File |Preferences menu. You can change page units tocentimeters (default is inches), default attributesfor text, lines, fills, and symbols, as well asturning the rulers and grid on or off.(Advanced) To set specific map setting, use theDialog Defaults tab in the Preferences dialogbox. Select the Dialog Defaults tab, open thecategory you would like to change the defaultfor, and select the particular option. Enter in thenew default for the Setting Value and specify theSetting Persistence.

Always Reset does not update the default setting when it is changed in a dialog. Every time thedialog is invoked, the setting is reset to the value in the setting file. Current Session only saves changesmade to the setting within the dialog during the current session only. The settings are not written to thesetting file and are not used the next time Surfer is started. All Sessions saves the changes made to thesetting within the dialog during the current session, and writes the changes to the setting file to be usedthe next time Surfer is started.

For example, to have the post map remember thelast used columns, choose the File | Preferences |Dialog Defaults menu commands. Scroll downto the Map Post heading, and click on the "+" toexpand the section. Click on the pXcol setting,and change the Setting Persistence to CurrentSession Only. Repeat for the other columns asneeded, and save the changes. When the postmap columns are changed, the changes will beremembered until you close Surfer.

II. Preparing a Base Map

Importing a base map

Surfer provides two ways to import base map files, the Map | Base Map menu, and the File | Importmenu. The Base Map option lets you use the map coordinates in the file for your base map. For vectorbase maps (e.g. DXF, GSB, SHP, BLN) you can change the attributes of all objects of the same type (alllines, fills, text fonts, symbols) though you can not modify individual objects. The Import option lets youbreak apart a base map to access individual items separately, though it does not support the use of mapcoordinates.

Georeferencing a bitmap base map

You can use a scanned image or other bitmap as a base map with the Base Map option. If the edges ofthe map are parallel with the coordinate system (not rotated), you can recalibrate the image to use mapcoordinates. After you load the bitmap as a base map, double-click or right-click on the map to displaythe Base Map dialog box. The Image Coordinates area contains edit boxes for the minimum andmaximum X and Y coordinates so you can change the coordinates of the lower left and upper rightcorners of the map.

If you have a TIF file georeferenced with an ESRI World File (TFW), you can use a simple script toimport the image into Surfer using the coordinates contained in the TFW file.

Posting symbols, values, and geophysical information

The Surfer Map | Post Map | New Post Map and New Classed Post Map menus control the posting ofsymbols, values, and geophysical information (shot points). The X, Y, and label values must be locatedin separate columns in the data file or worksheet. Simply go to Map | Post Map | New Post Map, selectthe data file and click Open. The post map is created. Double click on the post map to access the postmap properties. Specify the X and Y data columns on the General tab and specify the labels column onthe Labels tab.

To post two labels associated with eachpoint, create two post maps and overlay themby selecting the two post maps and using theMap | Overlay Maps menu command.

The classed post map can be used to displaysymbol properties based on a third (Z)column of data in the data file. Post maps andclassed post maps are easy ways to get anidea about the spatial distribution of yourdata points.

Selecting objects

The easiest way to select an object is to click the mouse pointer on theobject. This method selects the "top" object underlying the pointer. If youwould like to select another object underneath the pointer, hold down theCtrl key and click the mouse until the desired object is selected. You canview the selection handles or the name of the selected object in the Statusbar at the lower left edge of the window to see which object is selected.You can also select an object in the Object Manager. The Object

Manager lists all objects in your SRF file in an organized hierarchicaltree view. Simply click on the object you wish to select, or double clickon it to edit its properties.The F2 key is a shortcut for the Edit | Select All menu command.Tip: If you load several objects of the same type, such as base maps, intothe current window, right-click over the object either in the plot windowor in the Object Manager and go to Object ID. Here you can rename eachobject with a unique descriptive name. This name will show in the Object Manager and the Status Barwhen the object is selected.

Overlaying maps

When you first create maps in Surfer, they are not spatially related to each other. To snap the mapstogether according to their coordinates, you must overlay them. The easiest way to overlay maps is toselect the maps you want to overlay and use the Map | Overlay Maps menu command. If the only objectsyou have in the plot window are map objects, you can press F2 to Select All and then use the Map |Overlay Maps menu command.

Note: When you overlay maps, Surfer will reset the limits and scale of a map to display the entire mapwith the longest side set to 6 inches (15 cm). You can change this default behavior by changing theDialog Defaults under File | Preferences.

Scaling a map

The Scale tab under the map properties controls thescaling of a map. Simply double click on the map toget into the map properties and go to the Scale tab.The units in the Scale dialog box are page units (cm orin) and map units (whatever units your map is in). Forexample, if your page units are in cm and your map isin meters, and you want to specify a dimensionlessscale,

Such as 1:50,000 convert the scale to thecorresponding units:

1:50,000

1cm = 50,000cm

1cm = 500m

Making a scale bar

You can create a scale bar for a map by selecting themap and going to Map | Scale Bar. The cyclespacing is the value in map units between cycles.The label increment lets you specify a value for thelabels that is not based on map units. If your scalebar uses the same units as the map, the cyclespacing and label increment is the same. But if youwant a scale bar in kilometers and your data are inlatitude/longitude, you can specify different valuesin the Scale Bar dialog box.

For example, consider a lat/long map of Canada.

Using the formulas:

1° latitude = 110.6 km,

1° longitude = 111.3 km ·

cos(lat)= 111.3 ·

cos(51°)= 70.04 km

the ratio of scales between Y and X is 110.6 / 70 =1.58. Turn off the proportional XY scaling, andmultiply the default Y scale by 1.58.

To create a scale bar in kilometers for this map, theX equivalence is 1° = 70.04 km, or 1 km = 0.014°,or 1000 km = 14°. Thus the Cycle Spacing is set to14 (degrees) and thelabel increment is set to 1000 (km).

Pitfalls

• Objects that are not part of the map will not be moved when you change the scale.

• Overlaying a new map resets the scale to the default (6in or 15cm in the longest direction), sooverlay all maps before customizing the scale, and drawing any non-map objects (title box, legend).

Adding a legend and north arrow

You can use the drawing tools to add a legend or title box to your map. For best results, draw the legendrectangles and text as the last step in creating your final map.

You can add a north arrow to the map using the Draw | Symbol tool or menu. Choosing the tool ormenu changes the pointer to cross-hairs. Click the mouse to drop the default symbol at the desiredlocation. Double click on the symbol to display the Symbol Properties dialog box. Scroll down theSymbol display until the north arrow symbol is visible, click on it to select it, and click OK. If the map isrotated, you can select the symbol and use the Arrange | Rotate or Arrange | Free Rotate menucommands to rotate the symbol to the desired angle.

III. Gridding and Contouring

Loading a data file for gridding

If you know your data file, then you can go directly to the Grid | Data menu command, select a grid fileand click Open.

If you are unsure about the column layout or spatial distributionof your data file, there are a number of ways to familiarizeyourself with the data. You can use the File | Open menucommand to open the data file in the Surfer worksheet. Selectthe data and the Data | Statistics menu command displays theStatistics dialog box. You can select to calculate many usefulstatistics, including minimum, maximum, and number ofnumeric cells. Click OK and the statistics you selected areshown. It can help you spot anomalous values in a particularcolumn, such as negative values in a thickness or isopachcolumn.

To illustrate the spatial distribution of your data, you can alsomake a post map or a classed post map. The classed post mapdisplays the location of your data points and provides a way todisplay the location of various ranges of Z values. Data pointlabels can also be used if the data set is small.

Grid Data

Once you go to Grid | Data, select a datafile and click Open, the Grid Data dialogbox appears. This dialog box is the controlcenter for gridding. The Data Columns letyou specify the columns containing the X,Y, and Z values. If you are not sure whichcolumns to use, click the View Data buttonto examine the data file. The Statisticsbutton can also give you a look at the data,showing the Count (or number of datapoints) as well as the minimum, maximumand other statistical information. If thesevalues are not what you expect, open thedata file in a worksheet to verify that Surferis reading the file properly.

The Grid Line Geometry section of the Grid Data dialog box is where you can change parametersconcerning the size of the resulting grid file. Of particular importance is the Spacing in the X and Ydirections. The Spacing is directly linked to the # of Lines (grid lines). The # of Lines is the number ofgrid lines. The Spacing is the size for the grid cells (the spacing between the grid lines). The smaller thespacing, the higher the number of lines. By default, Surfer enters 100 for the number of lines in thelongest direction.

However, these values could be set to a value that better reflects the desired results of the map. If youwish to honor every data point, the ideal situation is to have a grid line intersection at each point. If thisgeometry results in too large a grid file from having toomany grid lines, a good compromise is to set the grid linespacing to the closest data point spacing. This value canbe estimated by examining a post or classed post map, orby using the Map | Digitize menu on the post map to getmore exact XY data point values from which you cancalculate the spacing using the formula:

In addition, since the grid line spacing affects the size ofthe grid cell, the smoothness of a blanking boundary willalso be affected. A large grid cell size will produce acoarse, "stair-step" or serrated boundary. You can reducethe grid cell size by reducing the Spacing or increasing the# of Lines values. The more grid lines are used to createthe grid, the finer the grid “mesh” will be and thesmoother the contour map will be. Large grid cell spacing produces a serrated boundary.

Selecting a gridding method

Unless you have specific information about your data set, we recommend using the default griddingmethod, which is kriging with a linear variogram. This method was selected as the default because itdoes a good job of gridding a wide variety or data sets. However, this method doesn't always produce thedesired results with every data set, so it sometimes pays to consider the other gridding methods.

The inverse distance method uses a "simple" distance weighted averaging method to calculate grid nodevalues. It does not extrapolate values beyond those found in the data file, but it tends to draw circles orbulls-eyes around each data point.

The kriging method uses trends in the map to extrapolate into areas of no data, sometimes resulting inminimum and maximum Z values in the grid that are beyond the values in the data file. This could beacceptable in a structure map or topography map, but not in an isopach map where the extrapolationproduces negative thickness values.

The minimum curvature method attempts to fit a surface to all the data values using an iterativeapproach. One drawback to this method is a tendency to "blow up", or extrapolate extremely large orsmall values, in areas of no data. Minimum curvature can extrapolate values beyond your data’s Z range.