ESCI 442/542: Introduction to Remote
Sensing
Last Updated 1/10/19
Introduction to the Global Positioning
System (GPS) and the collection of Ground Truth Data
Outline of Document
(Click on links to jump to a section below):
Garmin GPSmap60-C Basic Operation
Garmin
GPSmap60-C Create Waypoint (Ground Truth Site)
Garmin
GPSmap60-C Data Download
Add Coordinates to Attribute Table
What if can't get my data to download from the
Garmin?
Introduction; Ground Truth Data: In today's lab, I will present a brief lecture and then you will have a chance to use GPS units to map a few features here on campus.
Objective: Our objective is to use GPS units to provide you with a more in depth understanding of how GPS works and to familiarize you with the way in which you would use GPS to collect ground truth data for use in image classification. We will practice this a bit on campus but you will not be required to go off campus to collect any data. You will use our Garmin GPSMap60-C GPS units. Today’s lab will focus on the mechanics of using these specific GPS units.
Note: These GPS units are very expensive! A few safety precautions are in order.
- Use the wrist cord. Bouncing these things off the sidewalks is to be avoided at all costs.
- Although these units are water resistant, I'd rather not test the limits of their water resistance. If it even looks like rain, put the GPS unit in a Ziplock bag prior to going outside. You can push all the buttons you need to through the plastic.
Part A. On-campus Practice
Garmin GPSmap60: We will be using the Garmin GPSmap60s. We have about 15 of these that are available for sign-out.
We need to pay special attention to map projections and coordinate systems. Our image is in UTM, NAD27. Although you can make the Garmins display coordinates in UTM NAD27, these coordinates are actually stored and download using the WGS84 datum. This means that, back in the lab, when you download your data we will need to convert your coordinates from WGS84 to UTM NAD27 (more on this below).
Field Data collection: For today’s lab, we will practice collecting a few points on campus. When you go out in the field, I would like each of you to log at least 10 ground truth points. Feel free to work in groups if you would like. While you are in the field, I would encourage you to log the positions on the Garmin GPS units (as explained below) and you should also record coordinates, LULC codes and any offset information for each point using a pencil and paper as a backup. Your field data collection form might look something like this:
|
Northing (m) |
Easting (m) |
Level III |
Site |
|||||||
|
Site ID# |
Y-coordinate |
X-coordinate |
LULC code |
Description |
Comments |
|||||
|
DW1 |
5397690 |
537909 |
212 |
Grass |
||||||
|
DW2 |
5397730 |
537857 |
120 |
Commer. Bld. |
Parks Hall; actual location about 30m North of logged position |
|||||
Basic Operations For the Garmin GPSmap60-C GPS
Receiver
(These
instructions are modified from a document prepared by Stefan Freelan:
J:\saldata\tut_GPS\Garmin_GPSmap60\3_GPSmap60_howto.doc)
Turn Unit On - Press & hold Power button (top of unit next to antenna)
-
Unit comes on and searches for satellites (wait…)
-
Opens to Satellite screen with the Location and
Accuracy
Estimate at the of the screen
Turn Unit Off - Press and hold the Power button
(top of unit)
Switch Screens - Press Page
button (on right side) to switch between the
5
Main GPSmap60 Screens:
Satellite
– skyplot of satellites & satellite strength
Trip Computer – Info
on speed, bearing, ETA, etc.
Map
– w/waypoints & cities, can pan/zoom
Compass
– w/info on speed, ETA, etc.
Main
Menu – settings, manage tracks, etc.
*
Note: the GPSmap60-CS also has an Altimeter screen
Navigating within the GPSmap60
Screens and Selecting Items
- Use the Rocker Button
(large, center button w/arrows)
to “navigate” Up-Down-Left-Right to highlight items
-
Press ENTR (Enter) button to select a
highlighted item
Zoom In/Out (on the Map screen)
- Use the OUT button
(upper right) to Zoom Out
-
Use the IN button (upper left) to Zoom
In
Backlight On/Off - With unit on, press Power
button (top) once briefly
- Use Rocker
button to adjust up/down as desired
- Backlight goes
off in 15 seconds (or press ENTR)
***Change Units (Note that this step is
critical!!!) ***
- Main Menu screen
-
Select Setup, select Units
-
Adjust Position Format to: UTM
UPS
-
Adjust Map Datum to: NAD27 CONUS
- Adjust Distance to: Meters
Time of Day - Bottom of Main Menu screen
Check Battery - Top of any screen
Set Battery Type - Main Menu
screen – Select Setup – Select System
-
Under Battery Type, choose either:
Alkaline (disposable) or
NiMH (Nickel Metal Hydride – Rechargeable)
Change Battery - Lift metal loop on back of unit
-
Turn loop counterclockwise 1/4 turn
-
Remove back cover, replace batteries (2 AA)
-
Replace cover, turn loop clockwise 1/4 turn and fold flat
* * * Turn Unit OFF when not in use to save battery * * *
Press Mark button, then from the Mark Waypoint screen:
Enter a Name for the new waypoint (this is your site ID#; you might consider using
your initials and a #, ex. DW1)
-
Use Rocker & ENTR buttons to highlight
the name at the
top of screen (by default a number 001, 002, etc)
-
Use Rocker & ENTR buttons to select
letters (to ‘type’)
-
When done entering letters, highlight OK on the
keyboard & press ENTR to close keyboard screen
Choose an Icon to represent the new waypoint on the map (Optional)
-
Use Rocker & ENTR buttons to select
the marker
symbol (by default a flag, next to name)
-
Use Rocker & ENTR buttons to select
an icon
Average multiple positions for better accuracy (Critical for our
application!!!)
- Use Rocker & ENTR buttons to select AVG
- Wait… (counter
= # of positions to be averaged) (suggest you go for
at least 20 positions)
- Use Rocker & ENTR buttons to select SAVE
-
Make sure you hit OK (see below) to Record Waypoint
Record Waypoint - (this is not Optional and
must be done in addition to any of the Optional steps above)
- Use Rocker & ENTR buttons to select OK at
the bottom of the Mark Waypoint screen
Data Downloading Back in the Lab:
NOTE ADDED 1/19/18: The points that you collected
on campus were just for practice. But after you have collected points in the BakerBay scene, you can follow the instructions below to
download your data and check these points for accuracy.
It will be critical for you to overlay each of your points on our image to insure proper alignment and to move any points if needed. The following instructions (edited from those created by Stefan Freelan: J:\saldata\tut_GPS\Garmin_GPSmap60\4_GPSmap60_to_ArcMap_transfer.doc) will walk you through this process.
Transferring GPS Data from the Garmin GPSmap60 to ArcMap
NOTE: These
instructions assume a certain degree of basic Windows operating system fluency
(coping files, creating folders, opening multiple applications, etc). If you do not understand the instructions, please ask
for help.
These instructions
are specific to the Spatial Analysis Lab (AH-16) computers and are customized
for local (Bellingham, WA) data and coordinate systems (UTM NAD27). Adaptations
will need to be made for other computers and/or other areas.
You will need a
Garmin GPSmap60-PC connection cable (hooks into the back of the GPS unit and
the PC), found on most SAL PC’s.
OPTIONAL: See also
J:\saldata\tut_GPS\Garmin_GPSmap60\Using_DNRGarmin.doc for an alternative
method of downloading data…
1. Connect the Cable
Connect the cable (from the back of
the computer) to the GPSmap60 (open the large rubber cover at top, right hand side of the
back of the unit and plug in the 4-prong connector). Note: the cable only fits
one way into the GPSmap60.
DO NOT FORCE IT – line up the small notch of the
plug with the guide.
2. Turn GPSmap60
ON (if it’s not already On)
- Press
and hold Power button on the top of the unit (next to antenna).
- If/when
prompted (because you are indoors), choose ‘Use with GPS off’
3. Open a your bakerBay image in
Arc ArcMap project file
- Open Windows Explorer or My Computer
- Browse to the J:\saldata\ESCI-442\Baker_Bay_ENVI\imagery
folder and copy the bakerbay2011.img and .hdr
file to your working directory on C;\temp
- Open ArcMap and
add
your Bakerbay2011 image. When it opens,
it will probably appear rather dark but don’t worry about it.
4. Open
DNRGPS & Download GPS data
(In AH-16: Start / All Programs / DNRGPS / DNRGPS)
- If prompted
to use the default projection, choose NO
- Go to GPS-FindGPS
5.
From the Waypoint menu choose Download
(wait for data
to download…)
- From the File menu, choose Save To
File…
- Browse to desired location
(C:/temp or U:/) and enter a name
- For Save as type: use ArcMapView ESRI
Shapefile (Unprojected)
(*.shp)
(Note options to save to text file, dbase file or kml
file…)
- Click Save
- Repeat Download / Save as File
process for Tracks (from
the Track menu)
- Save
as type: use ArcView Shapefile (Unprojected) (*.shp)
- For Output
Shape choose Line when prompted in the next
screen
6. View your data in ArcMap
Your GPS data should
be added automatically to the existing ArcMap project. NOTE: If your new
shapefile does not show up in your Table of Contents (the list of data layers
on the left side of the screen), click on the Source tab at the bottom
of the Table of Contents, then click on the Display tab to refresh the
list. At this point, you points will
not line up well at all with your image.
Each point will probably be off by about 100m. Don’t panic!
This is because your points come in from the Garmin unit using the WGS84
datum but our image is in UTM NAD27. We
need to reproject the coordinates. This is a multistep process.
6a. Reproject from WGS84 to NAD83: In ArcToolbox, go to Data Management Tools-Projections and
Transformations-Feature-Project
Input
Dataset or Feature Class: shapefile with your points
Input
Coordinate System: GCS_WGS_1984 (this is the default)
Output
Dataset or Feature Class: shapefile_NAD83 (stored IN
THE LOCATION YOU WANT – don’t assume the default location/name is correct)
Output
Coordinate System: click on the 
to bring up the Spatial Reference
Properties Dialog box- click Select.
Navigate
to Projected Coordinate Systems-UTM-NAD 1983-NAD 83
UTM Zone 10N.prj Click Add
Click Apply-OK
Geographic
Transformation (optional): (not really optional!!!): Select NAD_1983_To_WGS_1984
If there are any Geographic Transformations that were selected by default
select these and use the X button to delete/remove them
Click OK. A Project Dialog box will open and inform
you that the transformation is complete. The dialog message (lower right) will
indicate that the Projection is in progress and will briefly pop-up when the
process is complete. Your new data should be added to the map automatically (if
not select Add Data from the File menu and browse to the location where you
created it). You will get a Datum conflict between map and output warning
message, which you can ignore.
6b. Reproject from NAD83 to NAD27: Again,
In ArcToolbox, go to Data Management
Tools-Projections and Transformations-Feature-Project
Input
Dataset or Feature Class: shapefile_NAD83 with your points
Input
Coordinate System: NAD_1983_UTM_Zone_10N (this is the default)
Output
Dataset or Feature Class: shapefile_NAD27 (stored IN
THE LOCATION YOU WANT – don’t assume the default location/name is correct)
Output
Coordinate System: click on the to bring up the Spatial Reference
Properties Dialog box- click Select.
Navigate
to Projected Coordinate Systems-UTM-NAD
1927-NAD 1927 UTM Zone 10N.prj Click
Add
Click Apply-OK
Geographic Transformation (optional): (not really optional!!!): Select NAD_1927_To_NAD_1983_NADCON (this should be the default, but if not select it manually)
Click OK.
Your
points should now line up much better!
6c. Moving/Offsetting points: If one of your points does not line up perfectly or if you want to offset
one of your points (e.g. you logged a position adjacent to a building but you
want your point to be centered on the roof of the building), you can change
this. Go to the Editor dropdown and
select Start Editing 
. Then left click once on a point
to select it, then Left click, hold and drag the point to the correct
location. When you are finished editing
all points, go to Editor-Save Edits,
then Editor-Stop Editing.
6d. Adding coordinates to the
Attribute table: If you open the attribute table
for your points, you will note that it does not include the coordinates for
your points. To add this information to
the attribute table, go to the ArcToolbox and select WWU Tools-Add XY Coordinates. Then simply specify your points file as the
Input Feature and click OK. Reopen your
attribute table and the coordinates should be there. At this point, all you need to do is export
the attribute table and save it as a .dbf file.
You can open this in Excel to double check it and then e-mail it to me.
7.
OPTIONAL: Save your Map (to your U:\ drive)
- Save your .mxd
(File / Save As) to your U:\ drive or desired location
- Close ArcMap (File / Close)
8. REQUESTED:
Please Remove Files from the GPSmap60
Delete Waypoints: -
Press the FIND button and select Waypoints
- Press the MENU button
- Use Rocker & ENTR to select Delete
-
Choose All Symbols & press ENTR
-
Use Rocker to highlight Yes & press ENTR
Delete Active Track: - On
the Tracks screen, use the Rocker to highlight Clear
- Press ENTR
-
Use Rocker to highlight Yes & press ENTR
Delete Saved Tracks: - On the
Tracks screen, press the MENU button
- Use Rocker & ENTR to select Delete All Saved
-
Use Rocker to highlight Yes & press ENTR
***End of Stefan’s
instructions***
What if I can’t get my points downloaded from the Garmin? If you can’t get the download to work, there is another option, assuming that you have good field notes. Go to Excel and enter your data in a format that looks like this:
|
SiteID |
Ycoord |
Xcoord |
LULCcode |
|
DW1 |
5397690 |
537909 |
212 |
|
DW2 |
5397730 |
537857 |
120 |
NOTE THAT THERE ARE NO SPACES IN THE COLUMN HEADER NAMES AND NO SYMBOLS!!! Now go to File-Save As-Other Formats and save it as a “CVS (comma delimited)” file. This is a comma-delimited text file.
Then Open a Pre-made ArcMap project file
- Open Windows Explorer or My Computer
- Browse to the J:\saldata\esci442\segwwu folder
- Double-click on wwu2004cir_1m_utm.mxd to open a
pre-made ArcMap project (a simple
map of the south WWU campus)
In the Arc main toolbar, go to Tools-Add XY Data. In the Choose a table…. box, navigate to your .cvs file and then select the appropriate columns for the X and Y data values. Select OK and your points should plot on the image. Since you recorded these values directly from the Garmin in UTM NAD27, they should plot properly with no need to reproject. You may still need to Move or offset these points. If so, the easiest way to do this is simply to move your cursor to the correct location on the screen and note the UTM coordinates for this location at the very bottom of the Arc window. Then go back into Excel and enter these values into the correct column/row.
Part B. Ground-truth Data Collection (Note that you will NOT be required to complete this part.
Instructions below only intended to outline the procedure that you would use if
you were collecting data off campus)
The Study Area: Prior to going out into the field, take a look at the image. The image is located on the J-drive in the class subdirectory under J:\saldata\Esci442\Baker_Bay_ENVI and the image name is bakerbay2005.img. Grab the .hdr file as well. This is the same image that you used in our first lab. The pixel size is 25 meters. You might want to print out a paper copy of the image to take with you into the field. In order to help you avoid wandering off the edge of the image when you get into the field, you should refer to these coordinates:
Northern boundary UTM coordinate: 5,423,542 m N
Southern boundary UTM coordinate: 5,385,817 m N
Eastern boundary UTM coordinate: 595,130 m E
Western boundary UTM coordinate: 532,155 m E
For each ground truth point, make sure that your Y coordinate (the northing) is between the northern and southern boundary and that the X coordinate (the easting) is between the western and eastern boundary.
Size of ground truth sites: Each point you record should be within a given cover type. Be sure that the points you select are within a fairly large patch of a given cover type. How large is “fairly large?” Think about the size of a Landsat pixel (30m by 30 m). Select patches that are at least 4 or 5 pixels by 4 or 5 pixels. This translates to about 120 to 150 meters on a side. A football field is about 90 meters long. The point you record should be in the middle of your patch. In many cases, it will not be practical for you to go to the center of your patch. For example, you may be standing in a road and want to log the position of an adjacent stand of forest. You can do this by estimating the distance and direction (use a compass to get a bearing) to your intended location. Most of us are not particularly good at estimating distances. Think in terms of football fields (a football field with the end zones is about 100 meters). Do the best you can and definitely use a compass. You will need to take good notes for each of your locations.
Target Land Use and Land Cover (LULC) codes: We already have a great deal of data on certain cover types. I want you to focus on the following
|
Modified Anderson Level II/III LULC
codes for ENVI |
||
|
Anderson Level II LULC Codes |
Modified Level II/III LULC code for ENVI |
Class description |
|
0 |
0 |
Background |
|
11 |
110 |
Residential |
|
12 - 17 |
120 |
Urban or Built up lands |
|
211 |
211 |
Ag. Pasture/Grass *Priority* |
|
212-24 |
212 |
Crops *Priority* |
|
31-33 |
|
Does not occur here |
|
40 |
|
"Recent" clearcuts; anything cut since 1972 |
|
|
401 |
1973-79 clearcut from Boyce |
|
|
402 |
1979-85 clearcut from Boyce |
|
|
403 |
1985-88 clearcut from Boyce |
|
|
404 |
1988-92 clearcut from Boyce |
|
|
405 |
1992-95 clearcut from Boyce |
|
|
406 |
1995-2000 clearcut from Grace |
|
|
407 |
2000-2002 from Cohen |
|
|
408 |
2002-2005 from Wallin |
|
41, 43, 61 |
410 |
Deciduous forest *Priority* |
|
42 |
420 |
Conifer forest *Priority* |
|
51-54 |
510 |
Water |
|
71-77 |
710 |
Soil/rock *Priority* |
|
81-85 |
810 |
Alpine veg., non-forest *Priority* |
|
91, 92 |
910 |
Snow/ice (Permanent snowfields only) |
Calculating Offsets: In many some cases, you may have been standing on a road and you wanted the coordinates for a forest stand (for example) that may have been to the northeast of your location at an estimated distance (for example) of about 300 meters. How do you adjust your logged GPS UTM coordinated to these desired coordinates?
Well, you need to recall your high school trigonometry class. All of you did calculations like this many many times in high school. And you can’t remember how to do this, there is this thing called the “internet” where you can look up all sorts of stuff. But on the off chance that your computer is broken or you have never used the internet to do anything other than stream the last season of “Survivor” on Netflix, here is how this is done.
OR:
OR:
OR:
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