Thursday, May 19, 2011

Digitizing the Wacom Way

A key component of our land cover mapping is manual quality control.  We accomplish this though the application of "heads-up" digitizing techniques within ArcGIS.  A single project can often require tens of thousands of manual corrections made for a given project.  With so many edits even a minor improvement in per-polygon digitizing speed can yield huge gains.

We were intrigued by the possibility of using a pen-driven interactive display to perform manual corrections because most people have extensive experience drawing with pens, and are familiar and precise with their control.  This allows the end user to draw their edits in a natural fashion directly on a digital map.  We contacted the folks at Wacom who were kind enough to ship us their DTU-2231 to test in our production environment.

The DTU-2231 has 22” screen, which is bright and crisp.  There is a power button that switches the display on and off, and a display menu similar to what you would see on a standard monitor (brightness, contrast, screen position, etc.).  Also included is a stylus pen that can be stored behind the monitor in a recessed holster when not in use. The stylus is the size of a standard pen, and has three buttons: two buttons near the point and one button on the end.  The end button is similar to an eraser on a pencil.  The display ships with software that allows for customization of the buttons, sensitivity of the screen, and different profiles for different software installed on the computer.

In terms of the Wacom Tablet’s application in GIS Editing, several key advantages surfaced:
  • The tablet allows for a standard mouse to be connected, allowing the user to switch between the fast pen for editing and more “computer friendly” mouse for doing other things.
  • The software allows the user to enter custom “keystrokes” for the buttons. In the “customize mode” window of ArcGIS, the user is able to enter “shortcuts” for the editing tools. In our case, we have assigned “e” to switch to the feature selector tool, “c” to switch to the pan tool, and “{alt} + s” to save edits.  After assigning these shortcuts in ArcGIS, we assigned the stylus buttons to match: The “eraser” button is assigned to “save edits,” the primary button  is assigned to “feature select,” and the secondary button is assigned to “pan.” In assigning these shortcuts to the different buttons on the pen, we can easily create a feature, select a feature (to delete or reshape), pan the map and save our edits without ever having to move the mouse around the screen – all of these functions take place right on the stylus.
  • Edits are fast and precise
There are however some drawbacks:
  • When editing attribute changes need to be made, the pen can actually slow things down. A mouse is the most effective way to change a feature’s attributes since there is inevitably a lot of clicking that goes on.
  • The editing templates in ArcGIS 10 can “confuse” the pen and the custom buttons will no longer work. In ArcGIS 10’s editing templates, the user “preselects” the attributes for the polygon before going to create it. This creates a problem as the user must constantly be predefining the attributes before drawing. This problem can be fixed however by turning off the “create features using templates” in the “ArcMap Advanced Settings Utility.”
  • Another potential problem that we ran into occurs when individual users change the customized settings for their own purposes each session. Deciding on customized buttons is something that should be done as a group, as having to redefine the buttons every session can take 15 minutes to complete.   That is of course a human resource problem as opposed to a Wacom problem.

For our needs at the SAL, the Wacom Tablet represents a time effective tool for editing single data type vector datasets (i.e. editing a vector layer solely composed of polygons representing tree canopy). The editing process is fast, precise and natural.  We ended up purchasing the DTU-2231 and will likely purchase another one this summer.


chandra said...

Touchy article, had to share with my friends, keep posting!@bose

Anonymous said...

I've been looking for post likes this. Could anyone relate first hand on the usability and features of the DTU-2231 vs. the Cintiq 21-UX?

I'm struck by higher (lines per inch) resolution and other techspechs of the Cintiq - it's available for nearly the same price as the DTU.

Also, I would like to have some more info on using the tablet with build-in screen as a second display. Working on a quadcore workstation with quite a powerful graphic card, would there be perfomance issues to expect?

Unfortunately, the wacom-site seems barely usable for a comparison or proper information at all.

Please keep posting!

Jarlath O'Neil-Dunne said...

I would try contacting Wacom. They sometimes offer free demos.

Anonymous said...

@Jartlath: Thanks, good idea.
Do you think they would give us the Cintiq and the DTU at the same time?

BTW, I'd love to read more on your experiences. How does the tablet change your workflow? How's digitizing on screen different from with a mouse?

In our lab, we mainly split, join and construct polygons for further statistical analysis (in R and GIS). Sometimes, we need to digitize and georeference printed stuff. We do some training for students, and sometimes employ students for digitizing. We thought it would be helpful to have a tablet, but ATM it seems to be of limited interest to the majority of our staff... gotta do some nice presentation to convince them. ;)