Geophysik

Handling Paleomagnetic Data in Microstation

Handling paleomagnetic data in Microstation 3D-CAD

(this instruction was written by Martin Waldhör around 2000; although Microstation and Accudraw are still available, be aware of possible changes in software functionality and handling)

Small circle methods require the combined handling of structural and paleomagnetic data (bedding poles, remanences, small circles, small circle intersections). There is currently no adequate software, but CAD-programs are an option.

Microstation is a three-dimensional CAD software for drawing and construction. Advantages for palemagnetic work:

  • Large data sets can be handled, ordered on layers, grouped and with different colours and line styles, free to choose.
  • Vectors, great circles and small circles are hold as independent entities.
  • Viewing is possible from all directions as well as free zooming.
  • Data can be selected directly, edited, changed, copied and pasted to other programs.
  • Coordinates can always be written to ASCII-files and brought to spreadsheet programs.
  • You can rotate data, do reconstructions and forward-modelling, and create animated scenes (videos) for dynamic visualization of tectonic processes.
  • Associated programming languages allow to create own tools and user environment.

Disadvantages: Microstation is a professional graphic software. It is complicated to start and get familiar with; no equal-area projection is possible

Getting started

Microstation is available from www.bentley.com. Educational licences cost about 100 Euro. 3D-CAD programs require specific training. Tutorials are found in the technical reference and on the website of Bentley. Here we want to explain the most important differences to other graphical programs and specifically show how to create and handle directional data.

Some important points

  • Each action is written to file immediately. Use the undo all button to discard changes.
  • Left click is selecting, right click is cancelling action. Right+left click together is a snapping function (setting tentative points).
  • Context-menus on right-click are offered only occasionally.
  • Use shift, control and space key to constrain/modify actions or change the working modes of tools.
  • Accudraw (default: turned on) is an intuitive, semi-intelligent tool for navigation and construction in 3 dimensions using only one view window. It is a central function within Microstation.
  • Selecting a tool function, usually a further context tool box opens, offering several options. In the lower left of the screen, a text appears telling you the next step to do.

Most other functions are similar to desktop publishing programs.

Setting up a data file for directional data

First of all, download a drawing of the unit sphere (download spheredgn.zip). Then create a new 3D-file in the Microstation Manager (appears after start) by File-New... Important: select seed file seed3d.dgn, otherwise you end up in 2 dimensions. Then attach the file spheres.dgn as an external reference file (File - Reference - Functions - Attach ...). External reference files cannot be changed, but snapped to, selected and copied to clipboard. Open - or close - the necessary windows and arrange them. Use Rotate View (top, front, dynamic, etc.) to select different view directions for each window. To see ACS-coordinate tripod enable ACS-Triad in Settings - View Attributes (ACS: Auxiliary coordinate system).

Drawing directional data: single point keyin and script execution

Single point keyin:

Vectors are represented as points on the surface of the unit sphere. These points are created with the drawing tool place active point. Be sure to first set the active color and line weight to the desired values and to have activated Accudraw. Then put the focus (mouse) on the Accudraw-coordinate box and press P on the keyboard. The data point keyin box will open and x,y,z can be typed in.

Script execution:

All actions in Microstation can be written in ASCII-files which are executed as scripts line by line. When creating larger data sets, such an Ascii-file is produced with an Excel-template and executed in Microstation. Simply select the worksheet area where the script is written, copy and paste it as unformatted text to the Wordpad-program of Windows. Then select one of the tab-characters and remove all of them with the replace tool. Finally the file is saved in txt-format. Execution of a script file in Microstation is as follows: In the Help-menue, open the Keyin browser, then type @ followed by the path to the file (the file may have any extension). Pressing return or click on key in executes the file. Caution: any space character or other fault in the Ascii-file will prevent execution. Create remanences and bedding poles subsequently. Then layers can be created in the layer manager (with the names of the sites) and the data shifted to.

Drawing great and small circles:

Usually it is sufficient to draw vertical small circles only as lines in the x-y plane. If necessary, they can also be created as true circles using the tool place circle. To draw a planar object, a view window must be oriented such that its view plane is parallel to the plane of the object to draw. Then the center of the object is defined by snapping a tentative point or a point keyin and then the object's radius is defined. In most cases, it is easier to work with scripts than manually create graphical entities.

Rotating elements

Precisely rotating elements is already an advanced task in 3D-CAD. In Microstation Accudraw and snap functions must be used. Unless special ACS (auxiliary coordinate systems) are used, rotations are always going around axes parallel to the view direction of a view window - perpendicular to the drawing plane. In order to rotate around a specific axis, we first have to rotate one view window to the desired position. This is done with the Change View Rotation tool from the 3D View Control tool box (in the menu tool boxes). Type in a step in degrees, select a view window (1, 2, ...) and then click on the rotation arrows of the tripod in the tool box (at first sight this functionality is not evident).

Make sure to activate Accudraw. Select the elements to rotate and choose the rotate tool. Within the rotate toolbox, select the two points option for dynamic interactive rotation with the mouse, or the active angle option for a fix rotation angle. Then you are prompted to enter a pivot point (text line on lower left of the screen) and here comes the critical action: The correct pivot point is the center of the sphere with the coordinates (0,0,0). The first option is to use the single point keyin (with the focus on the Accudraw window, press P and type in 0,0,0 and press return; make sure to perform the rotation in the correct window).

The easier way is to snap the center point (0,0,0). This is done by left+right clicking with the cursor near the position of the center (in the window with the intended rotation plane). Repeat until the text line in the status bar displays the coordinates 0.0000, 0.0000, 0.0000. Confirm the snap selection with a left-click. With the rotation option 2 Points and the cursor in the rotation window, the Accudraw-compass will appear and you can interactively rotate the selected objects by moving the cursor. Press the space bar (focus on Accudraw tool box) to change the Accudraw coordinate readout from Cartesian to polar coordinates. Right-click rejects action, left-click confirms. To constrain the rotation angle during the action, put the focus on the Angle field of the Accudraw tool box and type in the desired value.

Writing coordinates to a file

This option is quite unique to Microstation (Autocad does apparently not have it) and a crucial tool for us. However, the procedure is a bit puzzling and will usually require several attempts. A useful hint: confirm text inputs with return and close each tool box before opening the next.

First, a tag set must be defined. In the main menu go to Element-Tags-Define. The Tag Sets box opens. Choose Add... and give a name, e.g. xyzcolor. Close the box (!) and open the box Generate Templates from the same menu. The previously defined tag set xyzcolor will appear. Select Report On All Elements, give it a Report File Name (e.g. xyz), press return (!) and select the tags required ($color, $x, $y, $z). Choose File-Save and give it a name (xyz.tmp). Now we have defined the tag set xyzcolor for extracting the data, a report file name (xyz.rpt) and a template file xyz.tmp for recurrent use. Close the tool box.

To make a report, select the points coordinates should be written for. Then open the box Generate Reports from the same menu. The xyz.tmp must appear, double-click it to add it to the templates for reports and click Done. If everything is right, the line Done Generating Reports appears on the lower status bar. The report has usually been saved to ...Bentley\Workspace\Projects\Untitled\out\xyz.rpt. It can be opened with an ASCII-editor or Excel. The coordinate numbers have to be divided by 10.000. Should it be empty, something was wrong and you have to try again. Finally, use xyz2DI.zip to convert x,y,z-values to D/I-values.

  • Download example file script-ms.zip: Creates the remanence vectors of 19 different sites on 19 different layers in Microstation.
  • Download Excel file vectors2dgn.zip to create Microstation script for remanences and bedding poles
  • Download example file spheredgn.zip: Unit sphere in Microstation
  • Download example file spheredwg.zip: Unit sphere in Autocad