Track length measurements


Confined track and semi-track lengths can be determined in either 2D and 3D using FastTracks. Several automatic and manual measurement tools are included for this purpose in the Tool Bar and these should only be used after the c-axis direction has been set. The automatic length tools are still experimental and, just as for automatic counting, will require some degree of manual review and correction after they have been run. These automatic tools can be run on the entire set of selected grains using the appropriate tools from the Tool Bar, or can be run on an individual grain by using the options in the pop-up menu accessed by right clicking on a particular grain in the grain list. Automatic length determinations can take several minutes and progress is shown in the progress bar at the bottom left of the main window.

For all length measurements, a vertical cross-section through a particular track in the image stack can be seen in the Cross Section Viewer window by selecting the Cross-section tool in the Tool Bar and then clicking on a particular track in the main window. The handle at either end of the tracks can be adjusted by clicking and dragging in the Cross-section Viewer. Results for all track dimension measurements can be accessed in tabulated form using the various options in the Data menu. For all 3D length measurements the vertical depth of the track is automatically adjusted by the refractive index for that mineral, the value for which is set in the Capture Settings window (Settings menu>Calibration Settings>Calibration tab).

Confined track lengths

Confined tracks lengths can be determined by selecting the appropriate tool in the Tool Bar –separate tools are provided for TINTs and TINCLEs, although normally only TINTs are used by most analysts. The data for the different measurements will be collated separately. Suitable confined tracks for measurement are located manually at the time of image capture and identified as ‘lengths’ in TrackWorks. Defined boxes around each identified confined track are captured as separate stacks in both transmitted and reflected light in length mode, or they can be measured wherever they occur in the normal count image sets. Once a particular confined track for measurement is located in FastTracks, select the correct length tool and focus the image on one end of a confined track. Click on that end, then refocus and click on the other end of the track. The projected length, true length, depth interval between the ends, dip, azimuth angle to c, and true angle to the c-axis are all determined automatically. Using the zoom feature in the main window by scrolling while holding down the space bar can assist in positioning the cursor at the track end, event when the image is pixelated.

Semi-track lengths

For semi-track lengths it is very important that the position of the surface plane in the transmitted light image stack is set before the measurement begins. This is shown by a small marker under the Focus slider at the bottom of the image pane in the main window. In more recently captured image sets this is set at the time of image capture in TrackWorks, but can also be set manually for the entire image set by entering the surface image number (e.g. 2, 3 etc.) in the Measurement Options pane of the Analysis Settings window and pressing Apply to All Grains.

A semi-track length can be determined manually by selecting the Semi-track length tool and clicking roughly in a track etch pit and dragging and refocussing to the end of the track. The surface end of the track is determined as the centroid of the track etch pit at the indicated surface level, so it is really only the end of the track that needs to be located carefully. The orientation of the each semi-track relative to the c-axis is determined automatically, assuming the c-axis is within the plane of the surface, which may be confirmed by the parallel alignment of the surface etch pits.