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PaleoGIS™ for ArcGIS™
The Rothwell Group, L. P.
PaleoGIS Plate Model Deformation
Table of Contents
PaleoGIS 4.3 contains functionality that allows regional deformation to be easily added to plate models. Once deformation has been added to the model, if deformation is enabled in PaleoGIS, then during reconstructions, in areas that have been modified for deformation, the plate model layers and all user vector layers will be deformed as part of the reconstruction. To facilitate adding deformation, PaleoGIS 4.3 includes a tool called the Deformation Assistant which provides graphical tools for defining and previewing deformation in the plate model “cookie cutter” layer.
The deformation functionality in PaleoGIS can be enabled or disabled. When it is turned off, models containing deformation will behave like a rigid models when they are reconstructed. Rigid models that don’t contain deformation will behave the same (i.e., as rigid models) regardless of whether or not deformation is enabled. To enable/disable deformation, open the PaleoGIS Configuration window and go to the Advanced Options tab. In the Deformation section at the top of the tab, check or uncheck the Enable deformation checkbox to turn on/off deformation:
Deformation ID: The plate’s DeformID that was assigned in Step 3 in the Getting Started section above.
Sequence Number: Any particular plate can have multiple “deformation events*” defined for it, allowing that plate to deform differently over different age ranges and/or deform in more than one area, i.e., there can be a sequence of deformations for a particular plate. As a result, each deformation event for the plate must be assigned a unique integer sequence number, with the youngest event having the lowest sequence number (0 is the minimum allowed) and subsequent older events having sequence numbers that are higher. For example, if the lowest sequence number is 0, then the next oldest could be 1 and then next oldest after that could be 2.
Note that the lowest number doesn’t have to be 0 and older events don’t have to be numbered in increments of 1 as long as the sequence goes from youngest to oldest (e.g.., the sequence numbers could be 1, 3, 8, 10 for a particular plate, where 1 is the youngest and 10 is the oldest). Even if there is only one deformation event defined for the plate, it must still be assigned a sequence number (i.e., 0).
*In this document, a “deformation event” refers to the deformation that is defined by a single row saved in the Deformation Table
Old Age: The age at which deformation starts for the current sequence number.
Young Age: The age at which deformation ends for the current sequence number.
Note: If the plate has multiple deformation events, it is ok for the age ranges for different sequence numbers to overlap.
In this example we’ll be adding deformation to a plate on the east coast of S. America that has been assigned the DeformID 111 (plate shown in yellow in the images below). The deformation will occur between 110 Ma and 135 Ma, when S. America and Africa are rifting apart.
Using the Motion, Anchors and Freeze buttons (as shown in the animation below) we can add motion vectors, anchors and freeze polygons to the plate to define how the plate will deform over the specified age range:
Hint: When the Deformation Assistant is open, an ArcMap edit session will be started. As a result, you can use the ArcMap Snapping Toolbar to turn on/off snapping. Snapping can be useful when adding deformation graphics to the plate.
After you’ve added the graphics to define the deformation, you can preview the deformation by entering a Preview Age (in Ma) and clicking the Preview button to see how the polygon will look at the specified age, as illustrated in the animation below. The Undo button will return the polygon to its undeformed shape.
You can continue to add, remove or modify motion vectors, anchors and freeze polygons until you are satisfied with the preview results. To remove unwanted deformation graphics, select the ones you want to remove using the ArcMap Select Elements arrow and then press the Delete key on your keyboard. If you want to remove all of the graphics, you can click the Clear button on the Deformation Assistant; however, this will also clear the Deformation ID, Sequence Number, Young Age and Old Age fields in the Deformation Assistant. Alternatively, in the ArcMap Edit menu, choose Select All Elements and then press the Delete key on your keyboard. Note that Undo (Ctrl-Z) and Redo (Ctrl-Y) will work when you are adding, removing and modifying the deformation graphics items, except after clicking the Clear button on the Deformation Assistant.
Once you are satisfied with how the plate deforms, click the Save Deformation button to save your work. When you do this a row will appear in the Deformation Table at the bottom of the Deformation Assistant (see animation below). If you later want to view/edit this deformation event, select the desired row in the table and then click the View on Map button. This will add your saved graphics to the map and populate the fields in the Create or Edit Deformation area with the saved values. You can now make any desired changes to the graphics or the Create or Edit Deformation fields and then click the Save Deformation button to save your changes. You will be warned that this deformation already exists, so you will need to click OK to finish the save.
If you only want to change the Deformation ID, Sequence Number, Young Age and/or Old Age values (i.e., no changes to the deformation graphics), you can make these changes directly in the Deformation Table and then click the Save Table Changes button to save your changes.
To remove an entire deformation event, select the desired row in the Deformation Table and click the Delete Deformation button. You will then need to click Yes in the warning dialog that appears to complete the deletion. You can select multiple rows to be deleted by holding down the Shift key while you select the rows.
The Deformation Assistant can be used in the present day map (the top data frame) or in reconstructed data frames. It can be very useful to add deformation while in a reconstructed data frame because this makes it easier to identify and correct overlaps and gaps between plates at various ages.
To use the Deformation Assistant in a reconstructed data frame, close the tool if it is currently open, do a reconstruction to the desired age, and then re-open the Deformation Assistant in the reconstructed data frame and add deformation using the same methods as for the present day. When you save the deformation, the motion vectors, anchors and freeze areas will be automatically un-reconstructed to their present day coordinates before being saved.
Deformation events saved in the present day or reconstructed maps can viewed or edited using the Deformation Assistant in any other reconstruction or the present day and the graphics will be placed in the appropriate geographic location when they are added to the map. Just remember to close the Deformation Assistant and then re-open it when the data frame that you plan to work in is active. Also, when working in reconstructed data frames, the Deformation Assistant will only work in the data frame for the last reconstruction performed, so if you want to work in a different age, you must first do a new reconstruction to that age before opening the Deformation Assistant; re-activating a previously reconstructed data frame won’t work.
If you’ve defined multiple deformation events for a plate, then you have the option when using the Preview button to preview only the deformation resulting from the graphics that are currently shown on the map or to preview the cumulative deformation caused by the entire deformation sequence.
To preview the entire sequence, check the Include entire sequence in preview option under the Preview Age text box. This is the default setting and it is useful when you are previewing deformation in the present day and you want to see be able to see a plate’s deformed shape at any age using a single click. It doesn’t matter which deformation event graphics are currently shown on the map for a particular plate; when this option is selected, the preview function will included any other deformation events in the sequence that have been previously saved for the same plate. Also, if you are currently defining a deformation event that hasn’t been saved yet (i.e., you’ve drawn the graphics and filled in the Create or Edit Deformation fields), this unsaved event will be included as part of the deformation preview.
To preview only the deformation caused by the deformation graphics that currently shown on the map, uncheck the Include entire sequence in preview option. This is useful if, for example, deformation is enabled and you are in a reconstructed data frame and the plate is already in its deformed shape as a result of deformation events that have been defined for the plate for ages earlier than the current reconstructed age. In this case, as you define the next deformation event, you will only want to preview the results of what you are currently working on since the plate is already in the shape it would be in when the current deformation is applied.
Note that if a plate has only one deformation event defined (saved or in progress), the preview results will be the same regardless if the Include entire sequence in preview option is checked or unchecked.
To keep this message from appearing and make the preview function work again on the cookie-cutter layer, re-select the cookie-cutter layer in the Table of Contents.
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