GPS: What do I need to collect Application Appropriate location data?

Transcription

1 GPS: What do I need to collect Application Appropriate location data? Bob Goodwin, GISP GIS/Remote Sensing Analyst Remote Sensing & GIS Research and Outreach Services, MSU IMAGIN Conference-Dearborn, MI May 2 nd, 2005

2 Recent Developments in GPS Recent Developments NAVSTAR GPS to start offering a new civilian signal called L2C on the next generation of satellites (Block IIR-M 2005) Blurring lines between Sports grade and GIS grade equipment and between GIS grade and Survey grade equipment becoming a continuum More competition in the GPS marketplace Shift toward mobile GIS in GPS equipment take your data with you Galileo to come online and GLONAAS retooling 2/ 29

3 Recent Developments in GPS Rapid growth in Differential GPS resources CORS Continuously Operating Reference Stations (CORS) Coast Guard Beacons Community DGPS stations Canadian DGPS (CDGPS) Satellite Based Augmentation Systems (WAAS, etc.) Private, Fee-based DGPS Canadian DGPS 3/ 29

4 GPS Resources DGPS: CORS National Geodetic Survey National CORS website Free correction data download Data available ~ 20 minutes after hour Data archived at 1 second interval for ONE DAY Data is archived as UTC time This is the default download location for many GPS software packages Must download at end of day before NGS Dumbs Down data 4/ 29

5 GPS Resources DGPS: CORS MDOT CORS State CORS website Free correction data download Data available ~ 20 minutes after hour Data archived at 1 second interval for ONE YEAR Data is archived as Standard time Much easier download than NGS Reatime broadcast as well 5/ 29

6 GPS Resources DGPS: Coast Guard Beacon The ground-based, 300 khz transmissions are problematic due to weak signal strength in west-central and southwest Michigan OK signal strength Weak signal strength Weak signal strength 6/ 29

7 GPS Resources DGPS: SBAS Satellite Based Augmentation Systems (SBAS) offer free realtime DGPS SBAS broadcast on same frequency NO EXTRA EQUIPMENT WAAS (Wide Area Augmentation System) Services primarily North America Sub-meter to 5 meter horizontal accuracy Broadcast satellite low to the horizon Transmitted on same frequency as GPS satellites EGNOS (European Geostationary Navigation Overlay System) Services primarily European countries MSAS (Multifunctional Transport Satellite-based Augmentation System) Services Asian countries 7/ 29

8 GPS Resources DGPS: Fee Based 8/ 29 Omnistar Correction Service

9 Differential Correction Local Base Station Uncorrected Differentially Corrected Data collected on Nov. 2002; Corrected by data from Lansing base station. WAAS failed to work as well 9/ 29

10 GPS Resources Fieldwork Planning Software Go to Trimble Website Download Planning software Download Ephemeris file 10 / 29

11 GPS Fieldwork Planning OK Great Outstanding Print out graphs for # satellites, PDOP, HDOP, VDOP, etc. 11 / 29

12 GPS Resources - Software GPS Utility - FREE Import data from Sports grade equipment and export to shapefile format in several coordinate systems (UTM, Stateplane, Lat/Lon) GPS Trackmaker - Inexpensive Creates and edits tracks, routes and waypoints Realtime tracking on raster backdrops Minnesota DNR Garmin program FREE Creates and edits tracks, routes and waypoints Works in ArcView for realtime tracking over GIS data layers 12 / 29

13 GPS Equipment Main Categories of GPS Equipment Sports Grade/Recreational GIS Grade/Mapping Survey Grade/Geodetic GISurvey grade 13 / 29

14 GPS Equipment Sports Grade Features/Capabilities Small, lightweight, handheld design Designed to Record Waypoints, Tracks and Routes Detailed navigation displays Display of proprietary maps (topos, roads, etc.) Horizontal accuracy is 3 to 40 meters Ability to receive WAAS corrections Cost varies between $100 and $1,500 depending on features, included maps and accessories Garmin, Magellan, Lowrance, Silva, etc., etc. 14 / 29

15 Sports Grade GPS Advantages Inexpensive Small Quick satellite acquisition Easy to use Good navigation features Ability to download and display map data along with your location Ability to receive WAAS realtime corrections Did I mention inexpensive?? 15 / 29

16 Sports Grade GPS Disadvantages Much less accurate position data than GIS or Survey grade equipment Inability to collect attribute data Inability to collect data for differential post processing Inability to configure for optimal data collection (DOP, SNR, etc.) Limited capability to export data into GIS formats Realtime WAAS corrections disappear in hostile GPS environments 16 / 29

17 Sports Grade GPS Getting the most out of Sports Grade equipment Data Transfer Capability Use a external antenna (e.g. mighty mouse) Do GPS planning religiously Work in open conditions as much as possible and use WAAS Utilize additional software, such as GPS Utility, to get data into a GIS Understand limitations of equipment Monitor the solar weather at the Solar Influences Data Center (SIDC) ~ WAAS does not work during solar storms! 17 / 29

18 GPS Equipment GIS Grade Features/Capabilities Handheld or backpack design Usually rugged construction DGPS capable realtime or post processing Multiple equipment configurations Cost varies from $2,000 to $11,000 Designed to collect accurate GIS level data Attribute data collection Leica, Sokkia, Thales, Trimble, etc. 18 / 29

19 GIS Grade GPS Advantages High positional accuracy Sub-meter horizontal typical Ability to configure for optimal data collection (SNR, DOP, Quality, etc.) More sophisticated antennas to receive signals in hostile GPS environments (forest cover, urban canyons, etc.) DGPS capability, either in realtime or by post processing Ability to collect attribute data about features Ability to export data in various GIS formats and various coordinate systems Usually, high level of product support 19 / 29

20 GIS Grade GPS Disadvantages Expensive as compared to sports grade equipment More difficult to use/requires training Mostly a result of increased capabilities Seemingly unlimited configurations make it difficult to select ideal equipment 20 / 29

21 GPS Equipment Sports and GIS Grade Configurations All-in-one or Separate components: receiver, datalogger, antenna, realtime DGPS GPS receiver integrated with beacon receiver GPS receiver integrated with pocket PC GPS receiver integrated with ruggedized pocket PC (TDS Recon) GPS receiver integrated with a laptop The weakest link will determine your accuracy 21 / 29

22 GIS Grade GPS Getting the most out of GIS grade equipment Gather data by point averaging Set configuration patterns to limit and improve data Use a external antenna in hostile GPS conditions Plan field season for leaf-off conditions if possible (spring or fall) Utilize offset capability Do GPS planning Always differentially correct your data preferably with a local Base Use detailed codelists/data dictionaries 22 / 29

23 GPS Equipment Survey Grade Features/Capabilities Dual frequency data collection Realtime code or realtime kinematic data collection Components include Receiver, Controller and Geodetic Antenna Cost - $20,000 + Leica, Sokkia, Thales, Trimble, etc. Trimble 5800 Leica Smart Station Total Station + GPS 23 / 29

24 Survey Grade GPS Main Advantage Very high horizontal and VERTICAL positional accuracy subcentimeter Disadvantages Very expensive relative to other GPS equipment Complicated to use Long occupation times Difficult to get optimum data in hostile GPS conditions (canopy) Applications Geodetic mapping and control 24 / 29

25 GPS Equipment GISurvey Grade Features/Capabilities Geared toward the land surveyor as an economical option Single frequency (L1 carrier phase) Capable of centimeter level data collection Takes advantage of base stations collecting Carrier Phase data May work with CORS data, depending on length of baseline 10 to 15 mile baseline Functions as a reference station or as a static or kinematic receiver Useful in open conditions where satellite lock is maintained Leica SR20 SOKKIA Stratus 25 / 29

26 Thanks for the info, but what should I use? Determine the best equipment based on 1. Needs Features and Capabilities Make sure you are getting the features you need to do your job What accuracy do you need? Do you need to collect attribution? Do you need mobile GIS? Do you need to do precise navigation? Don t buy unnecessary equipment Do you need realtime beacon if post processing will work? Don t scrimp on equipment Make sure you purchase what you need, such as a external antenna for work under forest canopy 26 / 29

27 Thanks for the info, but what should I use? 2. Product comparison Gather information from peers What do they use? Are they happy? Contact individual vendors for information Hardware and Software Narrow down choices to a few companies Compare similar GPS packages from several vendors Do a Head-To-Head data collection run Test in most difficult job situations (under canopy, near bldgs.) Make sure you are comparing Apples to Apples If a vendor is unwilling to do a Head-To-Head run, dump them 27 / 29

28 Thanks for the info, but what should I use? 3. Equipment quality Contact peers who own equipment Make sure the company has a history of quality equipment 4. Product support Ask for references so you can determine history of support Meet with the person who will become your tech. support person Make certain the company supports equipment as it ages Replacement hardware, firmware updates, etc. Determine the software update procedure (free, pay, etc.) 28 / 29

29 Thanks for the info, but what should I use? 5. Cost What is your need? Don t spend $5,000 when all you need is 10- meter accuracy Cost should not be your primary concern Money people don t often see why you need to spend $4,000 versus $300 for a GPS unit Primary concerns should be equipment capabilities, quality and flexibility, along with product support If two units are equal in terms of capabilities, support, etc. then select the least expensive option Many vendors offer educational discounts or have special deals, especially when trading in old equipment Partner with other departments to share equipment Rent equipment instead of purchasing 29 / 29

30 The field season is Here!! Questions?