D-ASM Mapping Hardware
Two computing options have been tested and are in use in Forest Service sketchmapping systems: a two-screen laptop-based system with a separate touchscreen, and a pen-tablet sketchmapping table (Figure on the right). Because of the potential for bright sunlight on the screen, the visibility of the map image on the touchscreen display is critical. We evaluated several touchscreens, which varied in screen size, brightness, and touchscreen technology. Resistive touchscreens have a membrane layer installed over a fine wire mesh grid in the screen; when this membrane is pressed on to the grid, a signal is sent to the computer, and the cursor jumps to that spot on the screen. Virtually any object can be used on the screen — a finger, an eraser, stylus, etc. This can be a disadvantage for sketchmapping, because any inadvertent touch to the screen may result in undesired actions. Many touchscreens have a rather small screen size (10.4 inches diagonal), which limits the amount of map area visible on the screen.
A supplier manufactured several screens to Forest Service specifications for early testing. These screens have 800 by 600 resolution, 12.1-inch diagonal screen size, 1500 nits brightness, and capacitive touchscreens. This type of touchscreen is activated by completion of an electrical circuit using a tethered stylus. There is no inadvertent activation of the resistive touchscreen because the screen can be activated only with the tethered pen. It should be noted that this system is quickly becoming obsolete and will no longer be supported by the Forest Health Technology Enterprise Team.
Pen-tablet PCs were also tested as an alternative platform for the D-ASM. The advantages of the pen tablet for use in sketchmapping include a smaller, simpler hardware profile and fewer cables. The disadvantages include a smaller screen area and decreased screen visibility in full sunlight.
We have tested many GPS receivers, and it seems that any receiver capable of producing an NMEA 0813 output string will be compatible with the software. Expensive, survey-grade receivers are not necessary; various recreation-grade units are adequate for the task. The GPS signal enters the PC via a COM port (USB or Serial) connection. Newer USB GPS units have the advantage of drawing power from the laptop PC. Wireless GPS receivers provide an attractive alternative, and testing of such receivers is ongoing.
Encyclopedia ID: p3367
