Twcc fr coordinates

Lab 4: Georeferencing & Coordinate Systems

Objectives

(and alignment with Temple University’s General Education Quantitative Literacy Requirements):

1) Learn how we can find a specific location by using geographical coordinate system (Understand quantitative models that describe real-world phenomena and recognize limitations of those models and AND Perform simple mathematical computations associated with a quantitative model and make conclusions based on the results)

2) Learn how cartographers model the shape of the earth with a geoid and an ellipsoid (Understand quantitative models that describe real-world phenomena and recognize limitations of those models)

3) Locate places using Latitude and Longitude degree measurements (Perform simple mathematical computations associated with a quantitative model and make conclusions based on the results)

4) Discuss the relevance of georeferencing to map accuracy and map making (Recognize, use, and appreciate mathematical thinking for solving problems that are part of everyday life)

Directions for this week’s lab: This lab proceeds in several steps:

a) Exercise your understanding geographic coordinates (i.e., longitude/latitude, hereafter long/lat)

b) Determine coordinates (long/lat) of a geographic feature or landmark using a GPS

c) Interact with various reference grids that use the coordinate system

d) Transform the notation and the coordinate system of your original location

Part A: Working with Latitude and Longitude

Go to this website: https://itouchmap.com/latlong.html, which is a Google Mashup that helps you find the coordinates for a location. Among the features of the site is an automatic conversion tool for switching the notation of long/lat measurements, expressing them in different formats on the left hand side of the box at below the map.

ANSWER THE FOLLOWING QUESTION IN THE SPACE BELOW:

1) What are the different formats? What do they mean? See the link below for help.

https://www.reddit.com/r/explainlikeimfive/comments/7njz2m/eli5_whats_the_difference_between_degrees_minutes/

2) Find the latitude and longitude expressed in both notation systems for four locations of your choosing. One should be north of the equator and east of the Prime Meridian, one north of the equator and west of the prime meridian, one south and west, one south and east). Zoom in and out in the map and find locations (either randomly or based on your curiosity), anything you find interesting and report that location’s coordinates.

The Zero Milepost in Washington, DC (north of equator, west of prime meridian)

Coordinates: 38.8951226,-77.0365565

Degrees DMS: N38°53’42.411”, W77°2’11.603”

In this case the 38.89 is a north latitude and 77.03 is a west longitude.

We are converting – these are the same coordinates – we are just using a different location.

Add your 4 locations here in both notion systems: You should have no problem finding them using the itouchmap website. Remember different locations for each hemisphere.

Part B: Georeferencing a Location

For this part of the lab, you will learn how to use your phone as a GPS. This presupposes you have a smart phone on a data plan.

NOTE: You should incur no costs getting through this lab. If do not have a smart phone with a data plan or if you would prefer not to use your device to complete this assignment, please contact me via email. You are welcome to complete this lab using an alternative technique.

But if you already have a phone, there is no reason on Earth not to learn how to use it as GPS receiver. And it’s really cool!

STEP ONE: Install GPS app

The first thing you need to do is install a free GPS receiver app. I demonstrated via a screenshot in the last two presentations is GPS Status because it is so simple. It is available for free for both Droid (see instructions below). I’m not an iPhone user, but I’ve test driven My GPS Coordinates (see instructions below). There are many other apps to choose from, and you may already have a GPS app installed on your phone. Some are better than others. Feel free to pick your own. If you’re new to this, use the tools I know because it’ll be easier to help you.

STEP TWO: Mark an object, landmark or location.

Using your phone, mark your current location.

Directions for GPS Status app (Droid): to mark the location, open the GPS app and tap the screen. You have the option to share your location. Send it to yourself by text or email. You also have an option to copy the image (at far right when you tap the screen). This creates a screen shot of the GPS status screen. You can also send this to yourself or observe it later. Or if you just want to write it down, that’s fine to.

In the example screenshot I provide these are in the second to last row, written as Latitude and Longitude. Make a note of how they appear: (39°2.292’N, 77°6.161’W). These are not in DD! To change how these coordinates appear, I can change the setting of the app. To do so, tap the screen, click on the icon at top left (three lines). And then tap Settings. Then tap on “Units & Formatting”, then on “Location Format [DD.DDDDDD°]”. You’ll see a list of possible formats. Make a note of how the coordinates of your location are expressed in the following formats: DD.DDDDDD°, DD°MM.MMM, and DD°MM’SS.S”. To do this change the setting and make a note of both latitude and longitude are expressed by writing down the #s or sharing them with yourself.

Instructions for Apple ios:

C:\Users\chask\Box Sync\GUS 0821_Digital Mapping\Data&Images\MyGPSCoord_iphoneScreenshot.PNGTo note your location, open the My GPS Coordinates app and observe the lat/long. You have the option to share your location. Send it to yourself by text or email. You can also create a screen shot of the GPS status screen by pushing the power and home buttons on your phone at the same time. You can also send this to yourself or observe it later. Or if you just want to write it down, that’s fine to.

What you want to know is the coordinates of your location (long/lat) in Decimal Degrees (DD).

In the example screenshot I provide the coordinates are written as Latitude and Longitude. Make a note of how they appear: (). These are not in DD (they are default in coordiantes)! To change how these coordinates appear, click on the Settings icon at upper right, then select “Settings” and “Coordinate format”. There, you can change from decimal degrees [DD.DDDDDD°]” to other formats. Make a note of how the coordinates of your location are expressed in the following formats: decimal degrees (DD.DDDDDD°), degrees/minutes (DD°MM.MMM), and degrees/minutes/seconds (DD°MM’SS.S”).

Deliverable for Part B (responses should be inserted immediately below this list):

1) Note the coordinates of the location you have picked in the formats listed above (below)

2) Explain what these different notations and formats are (DD.DDDDDD°, DD°MM.MMM, DD°MM’SS.S”). It will be helpful to think of this in terms of decimal degrees vs DMS. If you aren’t clear on the distinction, enter both in a google search (or review the lecture or go here: https://www.maptools.com/tutorials/lat_lon/formats or, for a more detailed look, try Wikipedia: https://en.wikipedia.org/wiki/Geographic_coordinate_conversion). Is the information they contain identical or different for each one?

3) Explain what latitude and longitude are. What precisely are you expressing with these numbers for long/lat?

Include your responses in this space.

Part C: Converting

Everything in Google Maps and all the ways of formatting the coordinates is based on the World Geodetic Survey of 1984 Datum (WGS84). That means that all of these share a basic coordinate system and an ellipsoid model of the Earth. So these numbers for latitude and longitude are expressed using the same coordinate system.

Sometimes our data come from the past, before the WGS84. So sometimes we need to convert from one coordinate reference systems to another.

Go to the World Coordinate Converter (http://twcc.fr/en/#) and pinpoint the location of the geographic coordinates of one of the areas you examined in lab #2. When you click on your location on the map, in the box on the right you will see something like this:

At right, you are seeing the coordinates of you location in DD based on the WGS84 datum. Note that you can switch from DD to DMS by selecting a different button at the below the coordinates. Below that, you can convert these coordinates into other coordinate systems based on other datums. Try this yourself. For instance, in my example above, I have the location of the zero milestone in WGS84 and have converted it to the North American Datum of 1983 (CSRS).

Using the converter, I can see how these coordinates differ in different coordinate referencing systems. For example, I have pasted in the coordinates that that the World Coordinate Converter initially gave me when I first clicked the map (WGS 84). I’ve then pasted in the coordinates for other coordinate referencing systems.

GPS (WGS84) (deg): 38.89518926454431, -77.03659012913704

AGD 66: 38.89519449995824, 77.03659012913704

ED 1950: 38.89599311557112, -77.03659012913704

MGI: 38.89113417049738, -77.04175419940549

PART C DELIVERABLE:

Insert your own converted coordinates (you can use your current location from part B) by using the World Coordinate Converter:

GPS (WGS84) (deg):

AGD 66:

ED 1950:

MGI

Are the coordinates the same or different? Explain how and why in a few sentences. What does our lecture about ellipsoids and the shape of the earth have to do with these slight changes?

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