GPS Data Collection. 1. Field Reconnaissance 2. Mission Planning. 3. Equipment Setup 4. Data Collection/Data Update 5.

Transcription

1 GPS 1. Field Reconnaissance 2. Mission Planning 1. Create a project 2. Build a data dictionary 3. Check satellite availability 3. Equipment Setup 4. /Data Update 5. Data Processing

2 Plan/prepare for conditions Weather Terrain Access Plan a route Keep project goals in mind Practice sound file management Use appropriate data collection techniques Transfer and process data ASAP Steps Required for Success Proper planning will ensure a smooth data collection session, and a resulting dataset with minimal editing and optimal accuracy.

3 usbdrive:\gpsdata\projectname Uncorrected (*.ssf) and corrected (*.cor) GPS data Data dictionaries (*.ddf) Satellite availability graphs usbdrive:\gisdata\projectname\shapefiles Exported shapefiles (*.shp, *.shx, *.dbf, *.prj, *.inf) usbdrive:\gisdata\projectname\reference Layers Supporting files (aerial photos, other GIS layers, etc.) File Management Prepare your folders ahead of time. Create a project in Pathfinder Office (PFO) and understand where PFO saves various types of files. In some cases, you might need to manually save files in specific locations (eg. data dictionaries and satellite availability graphs) as PFO does not have default locations for them. Once you export your data, you should create a Shapefiles folder under your GISdata project folder and move them there (do not leave files in the Export folder). Make sure the export log file (*.inf) travels with your shapefiles. Keep your supporting files in a Reference Layers folder under your GIS data project folder. Keeping your files organized throughout the entire project will save you time and headaches later. See Appendix F in the GPHY 357 lab manual for detailed file management info.

4 SSF Standard Storage Format COR Differentially corrected SSF files DDF Data dictionary files SID* Reference layers (aerial photos) File Management These file types are found in the USBdrive\GISdata\projectname folder. More file types will be introduced with the transition from GPS to GIS. * Multiresolution Seamless Image Database (compressed TIF file)

5 Positions: data describing a location Part of a feature Non-feature positions Points: positions averaged to a SINGLE set of x, y, z coordinates Lines/Areas Set of positions (vertices) forming a line or polygon EACH position has a set of coordinates One note about terminology here: positions are individual measurements that become part of a point, line or polygon feature. They can also be between feature positions in a GPS data file. The term points, on the other hand, refers to a point feature in which several positions are averaged. The Xs in the diagrams represent individual positions. The red triangle in the diagram below represents the averaged position for a point feature.

6 Stops/resumes logging positions Uses Go around an obstacle without logging positions Deal with a distraction/interruption Pause/Resume (Pause/Log) Pause/Resume is a useful technique to temporarily stop and then restart logging as needed. On the receiver this appears as Log/Pause. For example, if you are mapping a trail and you encounter a huge log across the trail, you could Pause logging, walk around the log, and then Resume logging when you are back in the trail on the other side of the obstruction. Or, if you are mapping and someone walks up to talk to you, you could Pause logging to avoid collecting a pile of features in one location, and then Resume logging when you are finished talking to the person.

7 Picks up a line or area after closing the feature Uses Map another feature Finish mapping after a break/next day Continue (line or polygon) Nest (point feature inside a line or polygon) Continue is used when you have mapped a line or area feature, and had to close it before it was finished. You can continue mapping the feature later by selecting Continue from the Options menu. For example, perhaps you stopped in the middle of a line feature because you saw a point you wanted to map. You can close the line feature, map the point, and then Continue the line feature later. An option for doing the same thing is called Nest this is used when you want to Nest a point feature inside a line feature. The result is the same (you end up with two separate features), but there are fewer keystrokes involved. Nesting only works with points, whereas you can use Continue after closing a line or area feature and then mapping any kind of feature.

8 Allows portions of a single line to have different attributes Uses Creates a line feature made up of sections with different attribute values (paved, dirt, cobble, concrete) Each section is actually a separate feature, but the sections are connected into one physical line Segmenting is a method for creating a new line feature quickly. When you click Options > Segment, the new line feature is created with all the attributes of the previous line feature. You can then change any attributes that are different, but you save time by avoiding re-typing the attributes that are the same. Segment (line)

9 Creates a point/line/area at a specified distance and direction from mapping location Allows you to map in the open where you are able to receive satellite signals Uses Avoid poor mapping conditions (multipath, #SVs, low PDOP) Avoid unsafe or uncomfortable environmental conditions (traffic, water, etc) Offsets are used when you can t physically occupy the feature you need to map. You can use offsets on points, lines and areas. There are several types of point offsets to choose from, the simplest being a distance/bearing offset. With lines and areas, you specify the distance and left or right. For highest accuracy, you should use a steel tape measure and a compass for point offsets. Offset (point, line or area)

10 LTI TruPulse 360 Offsets are easy to map using laser rangefinders. The rangefinder calculates the distance and bearing for you, so you don t need a tape measure and compass. However, they are not as accurate as using a tape measure and compass (barring any user measurement error). We have a LaserCraft Contour XLRic laser rangefinder which is accurate to +/- ½ foot (15 cm). The LTI TruPulse 360 is a lighter weight, less accurate (+/- 1 ft (30 cm), less expensive rangefinder. LaserCraft Contour XLRic

11 Records the same set of attributes as the last feature mapped Uses: Speeds up data collection when mapping multiple features of the same type Repeat is useful when you need to map several features of the same type with the same attributes. Genus: Picea Species: pungens ComName: Blue Spruce Height: 40 ft.

12 Averages a set of positions for an important location along a line or area corners, intersections This is not a point feature! It is a vertex along a line or area feature Averaged vertices can be used for lines or areas. It is great for features that have straight lines between vertices. For example, when mapping a rectangular parking lot, if you collect a vertex on each corner, you will have a much cleaner looking (and more accurate) polygon than if you walked around the entire perimeter storing positions as you travelled.

13 Uses direction and rate of travel to log the next position must be moving Uses Multipath conditions Line and area features Velocity filtering is a technique that is automatically enabled in TerraSync for line and area features. In high multipath areas, mapped line and area features may end up with multipath spikes. Velocity filtering removes spikes and improves position accuracy under these conditions. Velocity filtering is automatically enabled in TerraSync there are no user settings.

14 5 Things to Take Away Today 1. Plan for conditions, availability and project goals 2. File types and locations are important lost and/or disorganized data will waste your time 3. Data collection techniques affect project outcomes use advanced mapping techniques to collect a clean dataset 4. Know the difference between a position and a point feature 5. Download and process data ASAP Always remember when you are finished mapping to close your file, exit TerraSync and turn off the receiver. Files left open can easily get corrupted.