GPSmapper description and examples

Plotting captured GPS data on a bitmap image of a map

Accuracy Test

Data formats supported by GPSmapper

Importing from GPSacreage PDB files

Exporting to GPS data ArcView

Generating vector files from any scanned map image

Using a map image to calculate acreage

Index

I took a photograph of a city map for the area where I live, and used my Palm program GPSgrabber to capture a vector file of my driving around in the area of m home. Then I used GPSmapper to plot the vector on top of the roadmap. This is a simple example, but it helps to demonstrate the point that you can use almost any map (in this case just a photograph of a map) to generate vectors or plot your existing vectors. 

The vector file generated by GPSgrabber that used to generate this plot looked like this:

Here is the same track as above plotted on a much larger scale map for the entire Western Cape (Cape Town, South Africa) region.  GPSmapper automatically scales the vector correctly to the size of the bitmap after you calibrated it.

Index

Just how accurate is GPSmapper? The accuracy is dependent on the GPS accuracy, which can deviate by approximately 15 meters.  This means that for very small areas you can not expert very good accuracy. However, the larger the area you are measuring, the better the accuracy.

As a test, I drove around the same block in my neighbourhood about five times in order to establish if GPSmapper will give me consistent results.  The following table shows the results of my test:

In other words,  the maximum deviation from the average is about 0.26% (or 0.0392 acres).

The following picture show all five plots drawn over each other by GPSmapper.  In this picture, the grid size is set to 100 feet blocks.

It is obvious from this sample that some of the acreage differences can be attributed to the fact that the GPS did not always take its samples exactly on the corners.   If I had taken the time to slow down around the corners in order to make sure that at least one GPS measurement was taken each corner, then the Acreage calculations would have been more accurate and consistent.  However, I especially did not do that in order to proof the accuracy is not too bad even if I just drive normally while making the measurements. 

Index

GPSmapper has an intelligent parse that will automatically determine which input format you are using. The only thing is that you will have to follow a few simple rules, namely :

The following are examples of VALID input values :

Similarly the following are input values that are NOT VALID :

GPSmapper reads and writes normal text files.  In the case of grid map files they normally have a "*.csv" extension, and in the case of a vector file they have a "*.vec" extension.  This just makes it a bit easier to identify which is which.

This is an example of a Grid Map file (*.csv).

Please note the following about Grid Map files :

1.    The "Area" in the header can be replaced by "Marker" or "Track" to distinguish between Area, Marker or track input files.  Remember, for "Area" files the points must be part of a polygonal shape which GPSmapper  will automatically close, plot and calculate inner surface.  In the case of  a file marked "Track" it will not try to close the polygon and it will not calculate the area.  And for "Marker" file, GPSmapper will plot only crosses at the marker points and write the name of the marker next to it.

2.        All Grid Map files MUST have the extension ".csv".  If the extension is not "*.csv" then GPSmapper will treat it as a vector file.

3. It is not compulsory to have the preceding numbers.  In other words, the example above could also have looked like this:

However, in the case of "Marker" file these numbers actually represent the name of the marker.  They do not need to be a number, and can be a numerical strings for example:

4.        The Latitude and Longitude data can be any for the following formats : dd.ddd,  dd mm.mmm or dd mm ss.sss.   The program has a built in intelligent parser that enables it to automatically detect the input format.  

Difference between Grid and Vector files:

1. Grid files end with "*.csv" and Vector files end with "*.vec"

2.  When working with Grid files, you do not require a scanned bitmap image of the area, but Vector files are normally used in conjunction with scanned bitmap images of a map.

3.  The first word in the header of a grid file identifies it as either a Area, Tract, or Marker.  Area files are used to plot acreage, and the start point will automatically become the end point as well.  A Tract file will be used to plot roads and fences where the start and end point is not connected.  A Marker file is used to lot individual Markers on the map.   In Vector files, then first line is completely ignored. 

4. When you want to plot multiple Grid files, you select all of them and plot them all together.   Vector files can also be be used to plot multiple vectors, but instead of keeping different vectors in different files, you only need a blank line between different vectors to distinguish them from each other. Here is an example of a vector file that represent two different vectors:

GPSmapper provides an easy way to import GPS data that was captured on PalmOS PDA using the program called GPSacreage.

The interface works on the principle that every time you perform a Hotsync action between your Palm PDA and your PC, the database files where GPSacreage saves its captured data is automatically backed up on your computer. These files are in binary format, and as such it can not be read by normal text editors. But GPSmapper makes it possible to convert these binary files to text format. This means you can use GPSacreage to capture the GPS data for you and then use GPSmapper to plot the captured data on a PC.

To convert GPSacreage PDB files to text format you have to do the following:

1. Start GPSmapper and select Grid Maps at the top menu.
2. Press the button marked "Other Functions" in the Main menu.
3. Press the button marked "Convert" in the other functions menu.
4. * Select the GPSacreage PDB file that you wish to convert.
5. Select a filename and location where the converted text file will be written.
6. Press the "Convert" button at the bottom of the screen.
7. There is also a button that allows you to plot the converted text file as a map immeadiately after you converted it to text.

* Palm PDB files are backed up in a directory which normally resides in the same path where your Palm Desktop software is installed. It is usually saved under "HosyncID"\Backup directory. For example on my computer I found these PDB files in c:\Program Files\Palm\wterreb\Backup. On you computer it might be found on a slightly different location depending on where you chose to install your Palm Desktop software. The PDB files have the same name as you saved them in GPSacreage. The default name is "New Area.pdb" if you did not specify a name in GPSacreage.

GPSmapper has a simple interface that  allows you to export the selected files in a format the can be imported into ArcView.   There are many ways to import data into ArcView. This uses one of  the most basic and flexible methods.  The export file is a comma delimited text file with a header on the first line to describe your data.

Example: 

To import a text file into ArcView

Index

Look at this map picture of San Francisco Area.  I got this map from http://www.topozone.com/.  (Topozone is a great source for getting free map images).  Note that I marked the two calibration points A and B that I used to calibrate this map. Then I used GPSmapper to create a vector file of the two main runways of the airport in the circle.   This is as simple as clicking on the end points of both runways to create the following vector file of the airport runways:

Off course you can equally easy create larger vector files for roads, flight paths etc.  If everything you want to map does not fit on one scanned map, then use more that one map and afterwards just edit the vector file to combine the vectors created on the different maps.  This way you can created detailed vector files even for large areas.

Index

 Do you want to calculate acreage using only an area map, without the use of GPS?   Now can easily do this.  Just click on Start Acreage and then use GPSmapper to create a vector of the boundaries surrounding the area you are interested in.  When you are done, click on end Acreage.  The are will now be plotted as a grid map, and it automatically show acreage information. Example:

Using the map above I created a vector file (see the red borders) of the yellow airport area as shown below:

 When  GPSmapper plotted this as a gridmap, then we see that this area covers about 1644.875 acres :