Capturing Lat Long Coordinates at CBSP
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This document provides instructions for capturing GPS coordinates from a map. It discusses: - The goals of capturing coordinates from the Chattahoochee Bend State Park map for a scouting activity - Tools like the grid tool and corner tool for measuring coordinates in degrees-minutes-seconds format - How to translate locations on the map to the underlying latitude and longitude grid to obtain coordinates The overall aim is to help scouts and parents understand how to use mapping tools to capture waypoints for route planning and geocaching activities using a GPS receiver.
![Base Map: Topo Map Field Features
• Topographical Map
• Terrain Features
• Water (Blue)
• Woodlands & Vegetation (Green)
• Clear/Open Areas (White)
• Surface Elevation [Contour Lines] (Brown)
• Man-Made Items
• Most Items (Black)
• Major Highways (Red)
• Revisions
• Since Last Major Update (Purple)](https://image.slidesharecdn.com/capturinglat-longcoordinatescbsp180823final-180831031830/85/Capturing-Lat-Long-Coordinates-at-CBSP-17-320.jpg)
![Modeling Local (Small) Areas
• Local Areas (within 8 nm) are essentially considered flat (2D)
• Difference is less than 60 ft between longitude lines
• Horizontal Distances Between Longitude Lines Narrow Toward Poles
• At Equator, Distance between 1’ Longitude Lines is 1 nm
• At Poles, Distance between 1’ Longitude Lines is 0 nm
• Longitudinal Distance = Cosine (Latitude)
• For Our Recreational Distances by Hiking, Muscle Boating, etc.,
Actual Longitude Distance Differences are Negligible
• Therefore, 1’ Latitude x 1’ Longitude modeled as a rectangle
• At CHBSP (1 nm x 0.835 nm) [cosine (33˚26.000’)]](https://image.slidesharecdn.com/capturinglat-longcoordinatescbsp180823final-180831031830/85/Capturing-Lat-Long-Coordinates-at-CBSP-21-320.jpg)
Capturing Lat Long Coordinates at CBSP
- 1. Capturing Lat-Long Coordinates Chattahoochee River Odyssey Chattahoochee Bend State Park
- 2. Capturing Lat-Long Coordinates: CBSP • Goals • Mission • Route Planning Process • Base Map Characteristics • Lat-Long Capture Tools & Methods • Worksheet Assignment Completion
- 3. Goals • Complete Global Positioning System receiver (GPSr) requirements • Camping Merit Badge • 1st Class • Geocaching Merit Badge • Know How to Create a Route to a Campsite • Starting & End Points • Trail Junctions • Trails, Rivers, Roads • Man-Made Permanent Structures • Buildings, Foot Bridges • Use a Topographical Map
- 4. Presentation Goal • Help Parents Understand the Background Behind Measurement Tools • Avoids using tools without understanding why they work • Avoids using tools without understanding what the results mean • Help Parents Help Their Scouts with Worksheet Assignment • Scouts in 6th grade not familiar with cartesian coordinate system • (x,y) coordinates from basic algebra course • May not familiar with any coordinate system • Work with Scouts to figure out first 3 waypoints to get the hang of it • Show how to use the Corner Tool when the easier Grid Tool doesn’t work • Be their cheerleader!
- 5. Assignment: Find Lat-Long for 14 Waypoints • Using the CBSP Odyssey map and both tools provide find and record Lat-Long coordinates in DD˚ MM.mm format for 14 of 19 Waypoints Latitude Longitude
- 6. Boldly Go! • This assignment is about capturing Lat-Long coordinates for waypoints on a trail to put into a GPS receiver • The goal is to use the tools to capture Waypoints from the map • This background information is largely irrelevant for doing it • It helps make sense of the measurements made (answers Why?) • Ultimately, eventually Scouts need to understand this to stay found • On this trip, if they understand a route is needed with waypoints along the way to get from their starting point to their destination, it’s enough! • Several other opportunities will arise to practice • Next opportunity is Troop backpacking trip in October (5 weeks from this trip)
- 7. Mission: Use a GPSr to Get to Camp • From CBSP Boat Ramp, Hike to North Platform Campground by 1700 • Process • Find a trail to get there • If possible, make or find GPS Route of the trail • Identify permanent features along the trail for use as Waypoints • Capture Lat-Long coordinates for each Waypoint • Load each Waypoint into a GPSr • Add Waypoints to the Route • Follow Route to Camp
- 8. Mission Impossible: How Not to Use GPSr • Load Campground Waypoint in GPSr, then take off along the trail from the boat ramp, especially without a GPS route or a map • Before GPS, hikers used trail maps with recognizable features • Length of trail determined • Expected rate of travel used to determine time of arrival • Collection points (things to find along the way) chosen before starting out • Thumbing used to keep take of location • Compass used to periodically confirm position and direction of travel • Time monitored to assess progress Properly used, a GPSr automates many of these functions
- 9. Length of Trail Determined • Procedure • Determine start and end points • Find the distance scale on the map • Lay a thread on the trail, from beginning to end • Stretch out thread • Use scale to measure length • Automation w GPSr • Load route into GPSr with a *.gpx file • Get one from a previous traveler or Make one with “My Google Maps” • Collect route by walking it using traditional land navigation methods • Trail length computed by GPSr
- 10. Determine Time of Arrival • Procedure • Establish start time • Using a rate of travel (between 1-2 mph) with Distance = Rate x Time formula • Calculate travel time (Distance and rate are known) • Add time to start time • Note: Use a rate of travel that includes breaks, etc. • Skipper uses 1 mph • Automation w GPSr • GPSr uses current location and historical rate travel on the route to estimate
- 11. Collection Points • Procedure • Collection points are identifiable locations to pass along the way • Trail crossings: Other trails, road, utility lines, rivers & creeks • Distinguishable landmarks: Boulder fields, buildings, hills, ditches • When planning the route, collection points are determined • Used as last-known-good points to get back to when lost • Automation w GPSr • Collection points are converted to waypoints loaded in GPSr
- 12. Thumbing • Procedure • Thumbing is keeping track of where you are with thumb on map whole way • Requires keeping map out, updating where you are while moving • Typically, not doing this is the major reason for getting lost • Automation w GPSr • GPSr keeps track of where you’ve been and where you’re going • Better GPSrs have embedded maps to show terrain relative to location
- 13. Compass Use • Procedure • Arguably unnecessary unless lost • Thumbing and keeping the map oriented is the preferred way to travel • Used to orient map when the terrain is featureless (everything looks to same) • Ex. Heavily forested area, desert • Best use is going cross-country (not using trails, roads, creeks, or other handrails) • Be sure to adjust for declination (aka variation in nautical world) • Can be used to figure out which way to turn • Automation w GPSr • GPSr keeps terrain map oriented • Better GPSrs have built-in compass, in both True and Magnetic
- 14. Time Monitoring • Procedure • Monitor time on a watch • Use results for computations • Time of Arrival • Time to Sundown • Civil Twilight, Nautical Twilight, Astronomical Twilight • Travel Rate • Automation w GPSr • GPSr keeps track of time for use in computations
- 15. Conclusion: Route Planning & Travel • GPSr does not replace use of procedures for planning & travel • Land navigation skills must be applied, whether GPS is used or not • Land navigation techniques must be used with GPSr assistance • Batteries go dead • Receivers break • GPSrs are dropped beyond reach • Satellite coverage may be blocked • GPS can be incorrectly used • Wrong datum • Wrong units • Waypoints input incorrectly
- 16. Bottom Line for Traveling with GPSr • Land navigation procedures used to provide data to GPSr for planning • Really can’t just put the endpoint in, then go • Can easily get off track (if there ever was one) • Without a map too, getting lost is easy because it takes longer to figure that out • A route must be determined and waypoints captured • Better defined routes lead to more realistic results • Always use GPSr together with a map • Carry a compass, just in case • Continuously validate GPSr representation independently • Does your knowledge of travel agree what GPSr is showing you?
- 17. Base Map: Topo Map Field Features • Topographical Map • Terrain Features • Water (Blue) • Woodlands & Vegetation (Green) • Clear/Open Areas (White) • Surface Elevation [Contour Lines] (Brown) • Man-Made Items • Most Items (Black) • Major Highways (Red) • Revisions • Since Last Major Update (Purple)
- 18. Capturing Lat-Long Coordinates for Waypoints • Use annotated Base Map • Use knowledge of how Lat-Long lines are laid out • Understand modeling of round Earth as flat Earth • Use tools to capture degree distances: Lat & Long • Input results into GPSr as Waypoints Note: Degree Distance is the change of degrees between two points, which can be converted to spatial distance, regardless of zooming
- 19. Base Map: Topo Map Resolution • Typically 1:24,000 (24K) • 1 unit = 24000 units • 1 in = 2000 ft • As a result • Many features are abstracted into a larger component • Contour lines show 20’ elevation changes • Comparatively insignificant items are too small to care about (causes clutter) • Therefore • Detailed maps of features the maker cares about must be made • To see such items, they are much bigger than they are at scale • Actual representations of their locations are tiny dots (lat-long positions (waypoints))
- 20. Base Map: Zooming • Zooming Destroys 1:24K Relationship for distance only • Terrain features do not improve or get worse by zooming • Greater detail (resolution) is not achieved by zooming in • Resolution does not get worse by zooming out • Zooming does allow better spatial resolution by zooming in • Therefore • Distance relationships are maintained by lat-long lines • 1’ (1 minute) latitude always equals 1 nm (nautical mile) • At theoretical surface of the Earth, modeled as a sphere (ball)
- 21. Modeling Local (Small) Areas • Local Areas (within 8 nm) are essentially considered flat (2D) • Difference is less than 60 ft between longitude lines • Horizontal Distances Between Longitude Lines Narrow Toward Poles • At Equator, Distance between 1’ Longitude Lines is 1 nm • At Poles, Distance between 1’ Longitude Lines is 0 nm • Longitudinal Distance = Cosine (Latitude) • For Our Recreational Distances by Hiking, Muscle Boating, etc., Actual Longitude Distance Differences are Negligible • Therefore, 1’ Latitude x 1’ Longitude modeled as a rectangle • At CHBSP (1 nm x 0.835 nm) [cosine (33˚26.000’)]
- 22. Base Map: Lat-Long Lines • Lat-Long Lines Usually Drawn in multiples of 1’ Apart • Makes use of 1’ latitude = 1 nm • For CBSP Odyssey, lines are 1’ apart • West Point Lake, lines are 1’ apart • Pensacola Harbor, lines are 2’ apart • Open ocean, lines are 5’ apart • As larger areas are covered (zooming out), lines spaced farther apart • As smaller areas are covered (zooming in), lines drawn closer together • CHBP Odyssey map zooms in, making 1’ lat lines about 3 inches apart
- 23. CHBSP Odyssey Map: Lat Long Lines Lat-Long Lines Drawn 1’ Apart Labeled in Degrees and Minutes - Latitude – Longitude - DD˚ MM’ - DD˚ MM’ Example - 3326-8501 - Lat is 3326 (33˚ 26’) N33˚ 26.000’ - Long is 8501 (85˚ 01’) W85˚ 01.000’ Note: Lower Section Cut-Off (Truncated) - 33256-8501 - Lat is 33256 (33˚ 26’ 01”) N33˚ 25.600’ - Long is 8501 (85˚ 01’ 00”) W85˚ 01.000’
- 24. North America Lat-Long Relationships • Latitude Increases from Equator to North Pole • Equator: Latitude is 00˚ 00’ 00” (N00˚ 00.000’) • North Pole: Latitude is 90˚ 00’ 00” (N90˚ 00.000’) • CBSP: Latitude ~33˚ 26’ 00” (N33˚ 26.000’) • Longitude Increases from Prime Meridian to International Data Line • Greenwich, England: Longitude is -000˚ 00’ 00” (W00˚ 00.000’) • Int’l Date Line: Longitude is -180˚ 00’ 00” (W180˚ 00.000’) • CBSP: Longitude ~-085˚ 00’ 00” (W85˚ 00.000’) • For Simplicity • Negative sign (-) replaced by West (W) allowing increasing numbers east→west
- 25. Bottom-Line: Lat-Long Concepts Summarized • 1’ Latitude = 1 nm = 6076 ft = 1.15(1 m) = 1.15(5280 ft) • CBSP Lat-Long Lines Drawn 1’ Apart • Local Area is Small, so Distances Between Longitude Lines are Equal • Distance Between Longitude Lines is Cosine(Latitude) • Distance between longitude lines shorter than between latitude lines • 1’ longitude ≠ 1 nm • Only use latitude for distance (ruler) • Latitude increases as one goes north (always true north) • Longitude increases as one goes west
- 26. Tool Implications • Rectangular Tools Used to Directly Capture Lat-Long Coordinates • 1’ Latitude / 10 • 1/10 nm = 0.1(6076 ft) = 607.6 ft ≅ 600 ft • 0.1’ Latitude / 10 • ≅ 60 ft • 0.01’ Latitude / 10 (not used) • ≅ 6 ft • Resolution is much better than GPS provides to civilians (within 30’) • Therefore, Capture Lat-Long Coordinates as DD˚ MM.mm’ • Ex. 33˚ 26.52’ For Our Purposes, Specifying the Location of a Foot Bridge Within 60-120’ is Okay! You can See It at that Distance
- 27. Rectangular Tools • Any method measuring degrees from known Lat-long lines is valid • Origin is always at lower right-hand corner (in North America) • Latitude is a vertical distance up (north) a longitude line • Longitude is a horizontal distance left (west) along a latitude line • There are an infinite number of Lat-Long lines between 1’ Lat-Long lines • For our purposes 1000 lines (x.000) in either direction (taken from GPSr to plot on map) • We read coordinates w tools using 100 lines (x.00) in either direction (N-S, E-W) • GPSr resolution is good 30 ft, not 6 ft, so don’t bother measuring to thousandths • For simplicity, locations translated to drawn Lat-Long lines • Straight lines available to make direct measurements
- 28. Translating Lat Long Lines to Baseline Lines Goal - Directly measure degree distances to actual location along known Lat-Long lines Process - Draw a parallel line to latitude to baseline longitude line - Measure degree distance to the intersection to determine latitude - Draw a parallel line to longitude to baseline latitude line - Measure degree distance to the intersection to determine longitude
- 29. Some Methods of Translation • Any method to draw parallel and perpendicular lines to drawn Lat-Long lines • Methods • Corner Rule • Grids • Drafting Right-Angle Triangles • Parallel Rules • Pair of Credit Cards • Our Tools Uses a Combination of Methods • Grid Tool with major and minor grids, marked in 10ths • Corner Tool with 2 embedded scales, marked in 10ths
- 30. Grid Tool • 10x10 Rectangular Grid • Rectangle is 1’ Latitude high & 1’ Longitude wide • Each cell in grid 1/10’ latitude high and 1/10’ longitude high • 1/10 nm or 0.1 nm • Diagonal cells have an embedded 10x10 rectangular grid • 1/100 nm or 0.01 nm • Provide seconds of a degree in decimal form of a minute • DD˚ MM.mm’
- 31. Grid Tool • Origin at intersection of an drawn Lat-Long lines • Lower right-hand corner • Upper left-hand corner is placed on waypoint • Minor grid rotated about the origin until grid lines are parallel to drawn Lat-Long lines • Degree distance directly read at the origin for waypoint’s Lat-Long position Origin Base Longitude Base Latitude
- 32. Grid Tool Procedure Waypoint Origin Base Latitude N33˚ 26.000’ Base Longitude W84˚ 59.000’ 1. Corner placed on Waypoint 2. Grid Tool turned until lines of minor grids lie on base Lat-long lines forming the origin 3. Read down to determine degree offset to add to latitude 4. Read right to determine degree offset to add to latitude Example - Base Lat-Long - 3326 (N33˚ 26.000’) - 8459 (W84˚ 59.000’) - Latitude Offset - 27 (N33˚ 26.27’) - Longitude Offset - 43 (W84˚ 59.43’)
- 33. Grid Tool Use • Can be Used in Other Ways beyond scope of this presentation • Cell overlay grid to approximate position of waypoint visually • Degree-distance ruler to determine lengths in nautical miles • Grid Tool More Difficult to Use Without Full Cell • Also becomes more difficult when there isn’t a full cell below base cell • Grid Tool Cannot be Rapidly Field Built • Grid Tool is fixed at 1’ Latitude • Corner Tool is More Practical and Versatile
- 34. Corner Tool Versatility • Drawn Quickly and Easily in the Field • Scale can be drawn directly from latitude sides of map alone • Scale can be made to any desired length • Scale can be Used in Either Appropriate Direction • Latitude scales to read latitude offsets • Longitude scales to read longitude offsets • Numbers not written on the scale (counted in actual use) • Needs Use of Other Tools to Translate Waypoint Lat-Long to Baseline • Tools: Parallel Rules, Drafting Right Triangles • Field Improvised Tools: 2 Credit Cards, Orienteering Base Compass
- 35. What about When Grid Tool Doesn’t Work? • Grid tool works well when • The origin is visible • There is a full cell to the right and down • Corner tool solves the problem • First, translate waypoint to visible Lat-Long lines • Use latitude side of corner tool to measure along longitude lines • Use longitude side of corner tool to measure along latitude lines • Depending on direction tool is used determines whether to add or subtract • If latitude is measured down from a latitude north of location, subtract from 1.00 • If longitude is measure right from a longitude west of location, subtract from 1.00 • Otherwise, use similar to Grid tool
- 37. Get Latitude from a More North Latitude • Use Latitude Scale to measure degree distance • From more north latitude line, measure down longitude line • Subtract seconds of a degree from 1’ (1.00) • Add result to what should be lower righthand corner • Example • Flip tool horizontally & vertically • Measure down from 3326 (N 33˚ 26.000’) • Measure 0.22 • Subtract: 1.00 – 0.22 = 0.78 • Add to 3325 (N 33˚ 25.000’) invisible • Latitude = N 33˚ 25.78’
- 38. Get Longitude from a more East Longitude • Use Longitude Scale to measure degree distance • From more east longitude line, measure left along latitude line • Subtract seconds of a degree from 1’ (1.00) • Add result to baseline longitude line • Example • Use tool un-flipped in both directions • Measure left from 8500 (W 85˚ 00.000’) • Measure 0.68 • Add to 8500 (N 85˚ 00.000’) invisible • Latitude = W 85˚ 00.68’ • Trailhead is N33˚ 25.78’ W85˚ 00.68’
- 39. To Complete Worksheet Assignment • Find dots (Waypoints) on trail along river, leading to camp • Start at the Boat Ramp • Follow trail to North Platform Campground • Use either Grid Tool or Corner Tool to measure degree distance • Use Grid Tool when there is enough of the tool to align minor grids on latitude and longitude lines • Use Corner Tool when the Grid Tool doesn’t work (easily) or anytime • Use tools to measure hundredths of a minute • DD˚ MM.mm • Turn in assignment to Patrol Leader (Ben), Thursday, 7 Sep 18