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. We have Trimble GPSes available in the stock room but they are much harder to use (in my experience). The Trimble documentation is lacking so I recommend this tutorial (PDF).

Field Data Collection

Before starting, you'll want to make sure:

• Turn on the GPS as soon as you are outside
• Set the datum to "WGS 84" and the projection to "UTM". For the Garman 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.

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. St.

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.

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 make 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 in the GPS data. 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. 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.

Report

Create a report with a short introduction, methods, results, and conclusion. Your report should include a map and a summary of what you found for ground cover at the annex. Add your data sheet as an appendix (you can scan it if desired). You can use a "basemap" from ArcMap to show the relationship of your points to your benchmark but do not use one with labels. This only works if your data is in WGS 84!

Many of the Esri base maps include labels. You will be marked down if you turn in a map with cut-off text or tiny text so please do not use a base map with labels.

The content of the report is up to you. Think about what a reader would need if they were from a sponsor you were working for.

Homework Turn-In

Turn in an MS-Word "doc" file to Canvas. Make sure your report includes:

• An estimate and your insight on the uncertainty of this approach to data collection and its potential impact on your research.
• Make sure your maps, other figures, and tables are professional quality and ready to be published as a report.
• The Root Mean Squared Error (RMSE) of your benchmarks points compared to a point for the benchmark.
• Extra credit:
  • Add the uncertainty of the entire class's data versus just your group.

Creating Reports in MS-Word