Plant Surveys with a handheld GPS

Introduction

This lab introduces using hand-held GPS devices for research. This lab focuses on using them in relatively easy terrain for plant surveys. You'll be using a GPS to identify a location and then a "hoop" to estimate the plant cover at each location. You'll also be establishing a "benchmark" to esimate the accuracy of the GPS.

Scenario:

• You've been asked by Humboldt County GIS office to create a report on the invaisive plants around HSU's "Annex" building. They also want to know about the uncertinaty in your spatial data.

Learning Outcomes

By the end of this lab, you should be able to:

• Use a GPS Hand-held to gather data on the location of plants
• Bring data from a GPS into ArcGIS and create maps
• Describe the issues associated with accuracy of GPS units
• Esimate standard deviation and root-mean squared error (RSME) for coordinates
• Work in a team to collect field data.
  

Equipment

The GPS hand-held units we will be using are typical Garmin recreational-grade GPSes.

By far, the most critical step in using a GPS is to set the datum to WGS 84 and never change it! If you change the datum in the field, you will have data that is in two different datums and the GPS will not know which coordinates were collected with each datum. This makes the data unusable (I have seen this happen twice with field crews).

You will also need:

1. Baggies in case of rain
2. Extra batteries
3. The Protocol and Data Sheet
4. A 1 meter quadrate (circlar or square)

Note: We will be using inexpensive Garmin GSP hand-held units for this lab.

Field Data Collection

The instructions below are speficially for the Garmin 64st units. This video is for the Garmin eTrex units that remote students may be using.

• Turn on the GPS as soon as you are outside
• Set the datum to "WGS 84" and the projection to "UTM". For the Garmin 64st units:
  • Press "Menu" twice
  • Press "Enter" on "Setup"
  • Scroll down to "Position Setup" and press "Enter"
  • Use the scroll button and the "Enter" key to change the "Prosition Format" to "UTM UPS" and the "Map Datum" to "WGS 84".
• Note that changing the projection in a GPS does not change the way the data is collected or recorded as these are always in decimal degrees. This just changes what is displayed on the screen. However, changing the datum does change the data.
• There is no output for HDOP on these GPS units so we won't be recording it for this lab.
• To record a "point" just cilck the "Mark" button on the GPS. This will save the point as a "Waypoint" so they can be downloaded later.

Make sure you have the datum set to "WGS 84"!

Using the protocol, travel to the annex and record data on the plants surrounding the structure. Work as a team with one person using the GPS and hoop and the other recording information. Switch roles periodically so everyone develops all the skills.

If you are working on your own, this video will help you collect the data.

Make sure to record at least 3 points at the benchmark at the corner of the grass that is at the intersection of C St. and 14th.

Making a Map

Back in the computer lab, follow the steps below. Note that if you are familiar with other ways of brining data into ArcMap from a GPS, you can use them. You just need to make sure you have the data correctly projected to WGS 84, UTM Zone 10 North when done.

The steps below use ArcMap, this video will walk you thought downloading the GPS data to ArcGIS Pro. Then, this video will show you how to prepare the data for analysis.

1. Create a folder structure in "D:\TempData" as we have done before:
• 01_Originals
• 02_Working
• 03_Final
2. Download the data from the GPS into the "Originals" folder. There are a variety of methods for doing this but I find the most reliable (for Garmin GPSes) to be:
   1. Connect your GPS to your computer using a USB cable.
   2. If you don't have DNRGPS installed on your computer:
      1. Search for DNRGPS on the web. This will take you to the Minnesota Department of Natural Resources DNRGPS (formerly known as DNRGarmin) web site.
      2. Download and unzip the software.
   3. In the DNRGPS folder, double-click on the "dnrgps.exe" program.
   4. From the "GPS" menu, select "Connect to Default GPS" and then "Find GPS". If you get an error, make sure the GPS is properly connected and has the appropriate drivers installed (this should happen automatically when the GPS is connect but it can take a few minutes).
   5. In the "File Menu" select "Set Projection" and make sure the projection is set to "UTM zone 10N". This will add two columns to your data that provide UTM Eastings and Northings.
   6. From the "Way point" menu, select "Download".
   7. You should see data appear in the "Way points" tab.
   8. From the "File" menu, select "Save to.." -> "File..."
   9. Set the file type to "comma-delimited" and save the data with a good file name somewhere you can find it.
3. In ArcMap, select "File -> Add Data -> Add X,Y Data"
4. Browse to the "CSV" file you created.
5. Make sure the "X Field" and "Y Field" columns that ArcMap selects are the "x_proj" and y_proj" columns, respectively.
6. For the "Coordinate System of Input Coordinates", select WGS 84, UTM Zone 10 North (i.e. Projected Coordinate Systems -> UTM -> WGS84 -> Northern Hemisphere -> WGS 84 UTM Zone 10 N).
7. When you click "OK", you may receive an error that the file does not have an "Object-ID" field. This is OK and the error will go away when we convert the data to a shapefile.
8. The data should appear in ArcMap. If you don't see the data, right click on the layer and select "Zoom to Layer". If you see any problems at this point, you may need to go back through the steps carefully. You can also check your CSV file in a program like "NotePad". Note that if you check the file in Excel, Excel may convert your values to "currency" and only show a couple of digits after the decimal.
9. These steps will create an "Event" layer in ArcMap 10.x. These layers are temporary and cause a bunch of problems. Immediately export the data to a shapefile by right-clicking on the layer and selecting "Data -> Export Data". Make sure to save the file in your "Working" folder, give it a good name that you'll be able to recognize in the future, and set the "Save as type" to Shapefile..
10. Now is a good time to select "File -> New" to clear out ArcMap and then load your new file. If you load it first, ArcMap should pick up the UTM zone and display your data in UTM. Move your cursor around the screen while looking at the lower right corner of ArcMap as the coordinates should be in meters. If your eastings are large negative numbers, you probably loaded the background first, try selecting "File -> New" again and load your UTM dataset first.
11. Add a map with an appropriate background and symbology.

Note: If you have problems with DNRGPS, try attaching the GPS and dragging and dropping the appropriate "GPX" file into BlueSpray.

Analysis

Compute the standard of deviation for the eastings and northings for your benchmark measurements. An easy way to compute standard deviation is to open the CSV file in Excel and use the "stdev()" function on the x_proj and y_proj columns. Then, compute RMSE for the benchmark points. This video will help.

Next, exchange your data with the other groups in the class. How does the data compare? How will this effect your field efforts?

Note: You'll need to get together with the other groups to figure out the best way to exchange data.