This map is made by downloading data from a Garmin 76 to DNR Garmin, saving it in kml format, and inserting it into the My Maps part of Google Maps. It can also be seen in Google Earth.
November 2007 Archives
USA Photomaps is a great tool to use with a GPS and to explore an area you are working in. However, there are some limitations that you should consider.
Some of the data is old. This is controlled by the people at Terraserver. For most forest uses it doesn't matter much. It's more an issure where development has occurred, or if there were logging operations or other land changes.
USA Photomaps is a mapping tool, not a GIS. It's missing some functions you would expect. But you can't beat the price. Also, many times it's better to have a simpler tool and bring out the big guns later.
- USA Photomaps uses UTM coordinates, as does Terraserver. The maps are discontinuous between UTM zones. You have to keep scrolling to come to the next zone.
After Monday's class here are some of the things you should be able to do with USA Photomaps:
- Download and install the program.
- Open a new map location.
- Zoom in and out
- Switch between aerial photo and topo map views.
- Change the coordinate system view.
- Download and install DEM's to display contour lines
- Display contour lines and determine the contour interval.
- Connect a Garmin GPS receiver to the serial port.
- Configure USA Photomaps to connect to a Garmin GPS.
- Connect the receiver and download waypoints.
- Download and display a track (Hansel and Gretel breadcrumb trail)
- Print a map.
- Download and display TIGER Maps road network data.
This article by Frank Etelmen in today's Washington Post describes how many government agencies are adding GPS receivers to their vehicles to see where employees are going. In some cases workers have been fired for going shopping or running errands on the job. Some have had to reimburse their employers for unauthorized use. Orders for tracking systems have been growing rapidly.
Many workers have complained that this is too much of a Big Brother intrusion into their work. Some unions have negotiated non-firing for a first offense clauses in their contracts.
Obviously, this monitoring can be taken too far. But administrators say that they have a duty to make sure public resources are used for public purposes. Also, the tracking helps them plan better routes for snow-plowing, trash removal, school buses, and other services. It helps save fuel and money.
From a technical point of view, remember in class I said that GPS was a passive system, in that the US government doesn't know how many people or who is using GPS at any time. However, a GPS-equipped vehicle can record and store data as it is driven around. This data can be downloaded periodically or broadcast live back to a central office. These services are separate from the GPS. According to the article, there are many companies offering the services for an initial cost and a monthly maintenance fee. It will be interesting to see if management can continue to use these systems or if workers will find a way to revolt.
Here is a first step at mapping the track of our work yesterday. In today's world is a paper trail map preferable over an online map? Would it be better to have both?
The trail obviously will need work to connect from the housing development entrance to the trail without people getting misdirected.
Here are some things to keep in mind when using the Garmin 76 GPS receiver.
- If the receiver hasn't been used for a few weeks or more it will take longer to boot up. It needs to download a new almanac before it can get situated. Remember that Garmin receivers don't give you access to the almanac.
- The built-in antenna is at the top of the receiver. To get a signal the antenna has to have a clear view of the sky.
- You are more likely to get a good signal if you point to the southern sky, since we are well up in the northern hemisphere.
- The GPS receiver has its own internal coordinate system. It can convert to almost any coordinate system commonly used. You can later change your data to any coordinate system you need.
- It's best to stick to the WGS 84 datum as that is the one most commonly used with current maps. When you first use a receiver it's best to check the datum to avoid errors of up to 200 meters!
- The receiver will work under any weather conditions. It's not waterproof, so it should be protected in a heavy rain. Try a clear plastic bag. In below freezing conditions the batteries can lose power. Also, the LCD screen will not work as well in the cold.
Here is the data you can store on the GPS. The Garmins we use are considered recreation grade. Other brands may use different names, but they all do about the same thing.
- Waypoint -- a stored location in memory. The 76 can hold up to 500. You can increase the accuracy of the waypoint by averaging while you store it. You can also give it a unique name and choose a marker.
- Route -- a directed collection of waypoints that make a path. You can create a route as you save the waypoints or you can create it afterward. A route can be navigated in the original or reverse order.
- Track -- the saved path made as you walk with the receiver. It is analogous to the breadcrumb trail of Hansel and Gretel. In the setup menu you can change how often and how far apart the track points are recorded. You can also save tracks as individual files. Tracks will show up on the maps screen as you work.
During yesterday's lab we used the latitude/longitude ruler and UTM grid tool from Map Tools to find the coordinates of different features on the topographic maps. There are several ways you can improve the accuracy of your meaurements.
First, make sure the lines you drew on the map line up with the tick marks on the side of the map. The UTM ticks are inclined a bit from the main axis on the map (remember grid north) and it's easy to get them off center. Strictly speaking you don't need to draw lines on the map. You can get by with a long ruler in a pinch.
Know what the precision to which you are measuring. For example, the UTM grid is designed to read to 100 meter precision. Your answer should reflect that. With UTM we always read over and up, easting and northing.
The Lat/Long ruler has a 0.01minute side and a second side. Make sure you use the right one. since Longitudes increase from east to west in the western hemisphere we place the zero mark on the east guide line. I find it helps to frequently check that the zero and the 2.5 mark are lined up properly as I slide the ruler up and down the meridians.
Can anyone come up with other tips?
Topographic maps in the field are bulky and cumbersome unless they are folded properly. Here are a few demonstrations of how to do it right to make the whole map accessible.
This is an online version of an army manual that gives several options for folding.
This method gives an accordion folded map along the long way.
This site shows the directions only, with no diagrams. It seems easy enough to follow.
Here is a map of the route we followed for the land forms on topographic maps lab.
During yesterday's field trip yesterday there was a bit of confusion over our location at the third stop. At first I thought we were on Shriners Knob. But when I checked the GPS waypoints back in the office it was obvious that we were on the side of Sandy Ridge. Congratulations to those of you who figured it out in the field!
The picture above is a screen shot from USA Photomaps, a program you will be learning shortly. It shows the data over a topographic map.
Here is link to the pictures I took georeferenced over a map in Flickr. Another view of the photos is available in Google Maps here.