Basic GPS for Field Course

Transcription

1 Basic GPS for Field Course { Mingzhi Qu Ph.D. candidate, Dept. of Biology Queen s University July 2015 GPS devices can be found everywhere When we talk about GPS - What is the Global Positioning System? Ñ Brief history of GPS Ô Started development in 1973 Ô First four satellites launched in 1978 Ô Full Operational Capacity (FOC) reached on July 17, 1995 Ô System cost of $12 billion(eq to 55 B) Ô GPS provides both civilian and military positioning globally Ô GPS comprised of three segments Ò Space Segment (24 satellites plus spares) Ò Ground Segment (the ground control network) Ò User Segment (GPS receivers and their users) GPS is not the only position system in the world Global Positioning System (GPS) Galileo Positioning System (Galileo) Global Navigation Satellite System (GLONASS) BeiDou Navigation System (COMPASS) How Does GPS work? If the distance to: Ó 3 satellites is known a 2- dimensional position can be determined (Longitude & latitude). Ó 4 satellites is known a 3- dimensional position can be determined (Longitude, latitude, altitude) (Note: this is what you always want to have.) How Accurate is it? Ñ Depends on the type of receiver, and terrain. Ñ Average handheld receiver: Ó 10 to 15 meters old handheld devices Ó With Wide Area Augmentation System(WAAS), newer models accuracy up to 3 meters Ó Accuracy to about 10cm with Differential GPS More satellites more accurate position. Graphic of person standing in a 10 m circle Common handheld devices Differential GPS devices 1

2 Understand Positioning Ñ When we discuss our position, we always use some form of reference frame. Establish Positioning A geographic coordinate system is a coordinate system that enables every location on the earth to be specified by a set of numbers or letters. (e.g. Lat/long) I m about 10 Meters in front of you I m at North 31 degree 32 minute 53 seconds and East 120 minute 22 minute He lives next to the City Park We need a common language to communicate. I m at the center of universe The good and bad of the geographic coordinate system Projected Coordinate System Good: Covers every spot on the earth Bad: Not a linear unit. You cannot measure the distance through this system. Fair race? Walk from 80 N 55 E à 80 N 60 E vs Walk from 0 N 55 E à 0 N 60 E Defined on a flat, two- dimensional surface, has constant lengths, angles, and areas across the two dimensions Projected Coordinate System Transform three- dimensional surface to create a flat map sheet. This mathematical transformation is commonly referred to as a map projection. Is this a Projection? visualize shining a light through the earth onto a surface, called the projection surface. Imagine the earth'ʹs surface is clear with the graticule drawn on it. Wrap a piece of paper around the earth. A light at the center of the earth will cast the shadows of the graticule onto the piece of paper. You can now unwrap the paper and lay it flat. Flatten an orange peel it will tear. Representing the earth'ʹs surface in two dimensions causes distortion in the shape, area, distance, or direction of the data. 2

3 There are infinite number of projected coordinate system Projected coordinate system vs Geographic (lat/long) coordinate system N 75 N 60 N 45 N 30 N 15 N 0 N (Equator) 10,000,000m 8,000,000m 6,000,000m 4,000,000m 2,000,000m 0m 10,000,000m Different projections cause different types of distortions. Some projections are designed to minimize the distortion of one or two of the data'ʹs characteristics. e.g. A projection could maintain the area of a feature but alter its shape. 15 S 30 S 45 S 60 S 8,000,000m 6,000,000m 4,000,000m 2,000,000m 75 S 80 S 0m 0m 500,000m 1,000,000m UTM coordinate One of the most used coordinate systems UTM coordinate One of the most used coordinate systems The UTM system divides the Earth between 80 S and 84 N latitude into 60 zones, each 6 of longitude in width. Horizontal lines measure Northing Vertical lines measure Easting. UTM positions are read Easting first, then Northing. UTM Zone No. Easting Value 18T UTM Latitude Band Letter Northing Value 3

4 Question: 18T Diving board: 18T Boat house: meters 18T What s the direct distance between Main lounge and Diving board? meters All those things to set? What s the direct distance between Main lounge and Diving board? Diving board: 18T Boat house: 18T Northing differences (100) Easting differences(120) C=156m Pythagorean equation Ó Why do we care about all these numbers? Ô Because all GPS units are configured to work with multiple reference frames, anywhere in the world. They give far more information than is required for local navigation. Ô Practically, this means YOU must be able to configure a GPS to work correctly in YOUR zone (with your maps) and be able to extract the important numbers from a position screen. (UTMs are not single projection) Take home message Ñ Global Positioning System is a system name, and is not the only position system in the world Ñ 3 satellites gives you a 2- dimensional position, while 4 satellites gives you a a 3- dimensional position. Ñ Unprojected coordinate system: Ó e.g. Geographic coordinate system Ó based on spherical coordinates, degrees of latitude and lonitude. Not linear unit. Ñ Projected coordinate system: Ó e.g. UTM coordinate Ó Coverts spherical coordinates to flat, planar coordinates, Uses linear units Ñ Projection is the process transform three- dimensional surface to create a flat map sheet. Ñ UTM positions are read UTM Zone No. and Band Letter first, then start with Easting, and Northing. Basic operation of handheld GPS unit Mingzhi Qu Ph.D. candidate, Dept. of Biology { Queen s University July

5 What can a GPS unit do for field biologist? Ñ Provide your current position anywhere, anytime. Ñ Display a line of past positions (a track) and store them. Ñ Store a large number of known locations waypoints. Ñ Give you real- time estimates on your travel progress. What the GPS unit will NOT do? Ñ Will not: Ó Give much useful data without a map. Ó Replace map and compass. Ó Necessarily give an accurate indication of magnetic north or current heading. Ó Assist you in getting home unless you can tell it where home is. Ó Be accurate over short distances less than 15m. Ó Be of any use without batteries or a clear view of sky. Why handheld GPS NOT smartphone Ñ Software and maps Ó Maps for navigation vs Topographic map Ñ Accuracy Ó Better antenna for GPS handheld devices Ñ Durability and battery life Ó Water proof Ó AA battery Ó heavy duty button Install/Change batteries 1. Remove the battery cover by turning the D- ring 1/4 turn counter- clockwise and pulling up. 2. Insert the batteries, observing polarity. 3. Replace the battery cover. Turning the Device On or Off Press and hold turn device on/off Quickly press on the right of the device to to turn on/off the backlight Acquiring Satellite Signals It may take 30 to 60 seconds to acquire signals. Go outdoors to an open area. Wait while the device searches for satellites. A question mark flashes while the device determines your location. press PAGE -> choose MAIN MENU -> use ARROW key -> find SATELLITE -> press ENTER Record GPS coordinate Number and ID of satellites received. Indication of signal quality. Estimated position accuracy. This is a key item for accurate navigating. Press PAGE (on top of the power button) Until you see this screen appears 5

6 Setup Position Format, Map Datum Setting Waypoints( 航点 ) Waypoints are locations you record and store in the device. 1.(GPSmap 62s): From any page, press MARK. Main Menu Setup Units(eTrex) position format/heading(gpsmap 62s) Always check POSITION FORMAT for the first time to use new device (etrex): go to Menu- > MARK 2.Edit with STICK/ARROW if needed 3. Select DONE/OK Editing Waypoint Edit attribute when MARK (select attribute with ARROW button- > ENTER- > DONE) 2.From the main menu, select WAYPOINT MANAGER. (etrex):main Menu- >Find- >waypoint- >press PAGE- > Select a waypoint. Select an attribute (such as the name or location). Enter the new information. Select DONE. Always mark your HOME position before you travel GOTO Waypoint FIND WAYPOINT GOTO Once you have a waypoint, you can navigate to it using the Goto command. press FIND -> select WAYPOINT -> select GOTO/GO. Navigating to Waypoint Navigating to a waypoint: Gives compass bearing, Distance to point, Estimated time to get there, based on current rate of travel. Heading: Your moving direction. Bearing: The direction from your current location to a destination. 6

7 Be Careful with GOTO Normally directs you in a straight line as-the-crowflies. GPS tells you to go 3.8km at a bearing of 248 true. Have to look at the map to see what terrain is between the start and end position. Tracks( 航迹 ) Handheld GPS records a track log while you are moving. You can save these tracks and navigate to them later or go back when you getting lost. Managing Track Log Recording Make sure Track Log set to on. A Point About Accuracy GPSmap 62: Page- >Main Menu- >Setup- >tracks- >ENTER Check track Log > Record, Show On Map Check colour - >don t leave as transparent etrex Unit: Page- >Main Menu- >tracks- > setup- > 39 Do not leave this as transparent or no track will show on screen. When you walk into the woods, the sky is covered by trees, results in not enough satellites to get an accurate fix This is why you ALWAYS need your compass, map, and know where you are on the map. If you get lost save your track - use Tracback Always Remember! 1. Allow unit to lock on to 4 or more satellites. 2. ALWAYS save your starting point as a waypoint (let s call it home ) write it in your field notebook. 3. Clear the track log & old waypoints before starting a task. 4. Set the odometer/trip to zero. 5. Keep extra batteries and keep GPS warm. 6. Does NOT replace map & compass. Take map & compass with you. 7. Always check/set (according to map reference): Ó Ó Ó Position format Map datum North reference 7

8 The only way to.. be comfortable with your GPS is to practice, (on your sofa)..practice, (out for a walk) Ñ Always carry a small notebook and pencil (it works in the rain) when you travel in the field. Ñ Mark down your: Ó bearings, Ó current position waypoint before you go. A Notebook and Pencil are always useful What my friends think I do What my mom thinks I do What society thinks I do What my wife think I do What I think I do What I actually do Geotag & Geotagging Geotagged pictures Mingzhi Qu Ph.D. candidate, Dept. of Biology { Queen s University July 2015 Ñ What is geotagging Ó Geotagging is the process of adding geographical identification metadata to pictures, etc Ó These data usually consist of latitude and longitude coordinates, they can also include altitude, bearing, distance, accuracy data, and place names 8

9 What can Geotag do for field biologist? Ñ Provide positions information for your pictures don t need to record coordinator from GPS Ñ Help to document an place or a sample Ñ Playback your pictures in computer with track/waypoint information Ñ Provide what we call GPS verification proof that work in the field was indeed performed What Geotag will NOT do? Ñ Will not: Ó Replace GPS. Ó Be of any use without a working GPS or a clear view of sky. Ó Cannot use as marking waypoint A standard camera with GPS Unit GPS Receiver Camera These camera and smartphone come with GPS too geographical identification metadata Make sure your location service is ON Example - iphone: turn on Location services for your Camera to allow your iphone to save that data along with your photos. Tap into Settings, and then tap on Privacy. Next, tap on Location Services and make sure they are on. If they are already on, swipe down to the Camera app icon and toggle that switch to ON as well. Tap into your Photos app, and navigate to the Years, Collections, or Moments views. You ll see a heading above each section with where those photos were taken. Tap on the location header, and all the pictures from that section will appear on a map. 9

10 If you don t have a new camera with you Save your picture on your computer (mac) right click, get info (windows)right click, properties. Check Latitude and longitude information. Type these information in google maps, you will see the location of your picture Record: Latitude, longitude, Time, and Altitude SYNC! Record: Picture, Time Using appropriate software, The latitude and longitude recorded by your GPS unit are linked and saved to your photos! Using Google Earth Pro to measure your wetland { Mingzhi Qu Ph.D. candidate, Dept. of Biology Queen s University July 2015 Using Google Earth Pro to measure your wetland 1. Turn on Track Log Recording GPSmap 62: Page- >Main Menu- >Setup- >tracks- >ENTER Check track Log > Record, Show On Map Check colour - >don t leave as transparent etrex Unit: Page- >Main Menu- >tracks- > setup- > 2.Walk along the shoreline of the wetland 1. Allow unit to lock on to 4 or more satellites. 2. Mark important waypoints Clear the track log & old waypoints before starting a task. Do not leave this as transparent or no track will show on screen

11 3.Download tracks from GPS Devices 6. Open gpx file on Google Earth Pro and measure a. Open garmin basemap software b. Connect your Garmin GPS device to your computer c. Click download from device d. Click File - > Save as gpx Google Earth Pro is now free for download. Practice Time Using your smartphone as GPS alterative Waypoint + track log + geotagged pictures + proper software = Valuable Data you may use your smartphone and apps to record trails and waypoints. Here s an example using iphone apps Step 1: Download & Run app Step 2: get waypoint Ñ.Download trail tracker GPS from app store (free use for a week) Ñ Open app, allow app to get your current location, then tap start new trail Ñ Giving enough time to get satellite, you will see your location in Latitude and Longitude. Ñ Start recording, you will see waypoint button on top right, but it is gray. Just walk for several meters, you will able to add waypoint. Ñ Once done, click finish button - choose "ʺsave & Quit 11

12 Step 3: save your trail Step 4: Using google earth pro to analysis your data (1) Ñ Click results, you will see your recent trail, tap the trail to go full screen Ñ Click export button, choose.kml format. now you can sent trail to your address Ñ Download google earth pro, after installed, open.kml file with google earth pro, choose preference - > show la t/long - >Universal Transverse Mercator(UTM) Step 4: Using google earth pro to analysis your data (2) Ñ Right click any waypoint, choose get info and you will see you waypoint in UTM format. 12