How to digitize points for GIS?
August 31, 2011 Leave a comment
How to digitize points?
A Point Feature represents a geographic location of interest. It is normally identified on a map by a point symbol, and has associated with it coordinates that specify its location on the map. Additionally, it may have attribute information stored along with the position information.
Besides logging GPS positions as Point Features, you may also manually add Point Features on the iCMTGIS or iGPSGIS screen. You may wish to digitize one or more point locations to highlight them on the displayed background map to help with navigation, to put in the vertices of a poly-line or an Area Feature that you will be adding later, or to add attribute descriptions to places you have visited or inspected.
The digitizing functions are grouped under the Tools icon next to the Main Menu icon. By default, the Zoom-Fit Tool is displayed. Tap the pull-down arrow to display the tools available in your application.
Except for the Zoom-Fit Tool, these tool functions are context-sensitive. For example, when an Area Topic is active, the Add Area manually tool will also be active. Similarly, when a Point Topic is active, you will be able to digitize Points into that Point Topic.
Therefore, the fist step in digitizing a Point Feature on a background map is to create or activate a Point Topic.
To create a new Point Topic, tap the Main Menu, select Topic then select New Topic. Enter a Topic Name, such as “Corners”. Make sure the Type field shows: Point. Tap the green check mark to confirm the screen and return to the Map View.
To activate an existing Point Topic to add points to it, tap the Topic View icon on the upper-right corner of the main screen then select the desired Point Topic. Tap the Topic View icon again to hide the list of Topics.
Tap the Tools icon then tap its pull-down arrow. Select Add Point Manually.
Now, tap the points on the desired locations on the background map to drop the points onto the map. If you intend to mark the corners of a rectangular area then tap the four corner points.
You will notice that there is a tool at the top showing a little hand with a pointed index finger. This is a toggle switch that you can use to halt the point digitization and reactivate the regular touch-screen mode. For example, when you wish to use two fingers to zoom into or out of the map, you will first need to tap on this toggle to prevent unwanted points to be added to the map whenever you touch the map. Tap on this toggle again when you are ready to digitize additional points.
If there are existing Features on the map and you want a new point to snap to one of the existing Features, then tap the SnapTo Node Tool showing an arrow pointing to a node. When the SnapTo toggle is on, the point you add will be dropped on top of the nearest Point or node.
When done with the point digitization, tap the tool icon showing a blue dot to end the digitizing session.