OVERVIEW
The Conversion Process for ArcView 1
The Trimble Pathfinder Office software generates ArcView shapefiles directly. While the process is somewhat simpler than that for creating coverages, all the caveats about being sure that datum, projection, coordinate system, and units are correct, apply equally.
A note on the shapefile data structure: ESRI refers to the Arc View-sty le representation of geographic data as a "shapefile." The shapefile is, in fact, a set of files which reside in the same directory. A shapefile named "abc," then, might consist of the files abc.shp, abc.shx, and abc.dbf. When you bring these files up in ArcView you see only abc.shp in the table of contents. You should realize, however, that all the files beginning with "abc" are involved. Using the operating system to copy or rename them is a bad idea. Use the ArcView capabilities (e.g., Manage Data Sources) to manipulate shapefiles. The shapefile arrangement is not quite as complex as the UNIX or NT ArcInfo arrangement but it can be confusing nonetheless.
After conversion you will find the files that constitute the shapefile in the Pathfinder Office Project Export directory.
The Files That Document the Export Process
The record of the conversion process is placed in two text files named something like exp1204a.txt (where 1204A indicates the month, day, and a sequence letter) and c111315a.inf. These files will also be in the Export directory.
The "exp" file will look something like this: This file will give you a good idea of how the process went. This information is also available to you at the time the export process takes place; just ask to view the log of the export process. It is a good idea to at least look at the log when you do the export. Go back to the "exp" file if you run into any difficulty. (Note from the last lines that a third file is generated, buried deep in the general
Pathfinder Office program files directory, that tells what files were generated—probably no new information there.)
The file that has the GPS file name (in this case c111315a.inf) contains information about the setup used. This file is certainly worth reviewing if the data are to be used for any important purpose. Probably the file should be reviewed by at least two people if the data are to be published or used by the public.
This information is descriptive of the process. Of course, your mail interest is in the shapefile that is generated by the Export process. The Step by-Step section that follows will lead you through the manufacture of a shapefile.
STEP-BY-STEP
Bringing GPS Data to ArcView GIS: Major Steps
A summary of the steps required to produce a GIS shapefile from Trimble Navigation GPS data is as follows:
1. Collect data with a GPS receiver.
2. Load data into a PC—in the process SSF files are created.
3. Examine data graphically in the PC, and correct it, differentially and otherwise, as appropriate.
4. Convert data from Trimble format to an ESRI ArcView shapefile using Pathfinder Office (or other third party software), being especially careful to use the proper parameters for datum, projection, coordinate system, and units.
5. In ArcView add each shapefile as a theme to a view, and rename it (or copy it, giving it a new name). Repeat the process for as many shapefiles as you have.
6. Obtain other GIS data such as coverages you digitize, TIGER files, GRIDs, TINs, DEMs, DRGs, soils or image files, available commercially or from governmental sources.
7. Use ArcView to integrate the converted GPS data with other GIS data.
PROJECT 6a-A
In November of 1993 the students and faculty of the Department of Geography at the University of Kentucky participated in a cleanup of the Kentucky River.
They took a GPS receiver on their trek; the antenna was mounted on the roof of a garbage scow (originally built as a houseboat). One file they collected along the river, from a marina to an "island" in the river, is C111315A.SSF.
Using postprocessing differential correction, it was converted to C111315A.COR. In this project you will make an ArcView point theme from the COR file, using the Trimble software and Arc View.
Make a Shape file of a COR File
{_} Start Pathfinder Office in the usual way.
{__} In Pathfinder Office make a PROJECT named BOATTRIP_AV_yis (where yis represents your initials); set it up so that the associated folder is_:\GPS2GIS\RIVER_AV. Switch to that project.
{__} You should find a differentially corrected file C111315A.COR in your project’s main folder. Open it in Pathfinder Office. Map it and Time Line it. The image you see should look something like a fishhook—in keeping with our nautical theme; the GPS track was taken over a period of about 45 minutes starting around 10:00 A.M.
{__ } Under Pathfinder Office Options set the Distance Units to "US Survey Feet."2 Make the other distance variables relate to Feet as well. The North Reference should be True.
{__ } The Coordinate System should be selected by "Coordinate System and Zone." For the System use U.S. State Plane 1983. The Zone should be Kentucky North 1601. Measure altitude from mean sea level. Use the Defined Geoid. Make the Coordinate Units and Altitude Units U.S. Survey Feet.
{__ } Don’t change anything in Style of Display unless the Coordinate Order is not North/East or the Scale Format is not 1:X. The Time Zone should be Eastern Standard USA.
The process of making an Arc View theme from a COR file is complex enough, and error prone enough, that the Pathfinder Office software insists that you set the conversion up in advance.
You do this with an Export Setup file, to which you give a name. You may use this file for later exports— either exactly as it is or somewhat modified. There are seven major facets to the Export Setup file. In no particular order, they are:
• Data
• Output
• Attributes
• Units
• Position Filter
• Coordinate System
• Arc View Shapefile
{_} Bring up the Export window, by either picking Export under the Utilities menu item or by clicking on the Export icon on the Utilities toolbar. (See Figure 6—2.) In the window, under Input Files, Browse to find C111315A.COR in _:\GPS2GIS \RIVER_AV. Select it, then "Open" it.
{_} The next step is to pick a folder that will hold the exported shapefile. If you have set up the project correctly the default folder shown should be: _:\GPS2GIS\RIVER_AV\EXPORT.
There are three sample export setups that work with ESRI products.
• Sample ArcInfo (NT & UNIX) Generate Setup
• Sample ArcInfo (PC) Generate Setup
• Sample Arc View Shapefile Setup
{__ } From the drop-down menu under "Choose an Export Setup" find "Sample ArcView Shapefile Setup" and select it. Click "New" at the bottom of the window to bring up a "New Setup" window. (See Figure 6—3.) The idea here is to create a new setup that suits your needs, without changing the original setup. Choose "Copy of existing setup."
{_} Replace the text in the "Setup Name" window with AV_yis#1 to rename the new setup. Then OK the New Setup Window.
{__ } A window should appear3 entitled Export Setup Properties— AV_yis#1. The top portions should look like Figure 6—4. In this window are seven tabs, conforming to the list of seven facets listed above.
Figure 6-2. Exporting a GPS data file to a GIS format.
{__ } Start with the Data tab. You want to export "Features— Positions and Attributes." Pick Export All Features from the dropdown list. You want to include Not-in-Feature Positions. And you want one point per Not-in-Feature position. See Figure 6—5.
{__ } Under the "Output" tab, choose the option to combine all input files and place the results in the project export folder. (By default, Pathfinder Office will combine all of the input files into a single entity with a generic name such as "Posnpnt." If you want the original name of a file to be carried through during the export process, or if you are exporting multiple files whose output you want to keep separate, you may choose the option "For each input file create output Subfolder(s) of the same name.") For the System File Format choose DOS files unless you are using some other system and the options are not grayed out.
Figure 6-3. Creating a customized setup to make a shapefile.
Figure 6-4. Set seven properties for a successful ArcView export.
{__ } Under the Attributes tab, let’s export a couple of attributes as well as positions.4 Make checks by Time Recorded (under "All Feature Types") and Height (under "Point Features") as in Figure 6—6.
{__ } The Units tab: Here you will tell Pathfinder Office to use the Current Display settings, which should be US Survey Feet, Square Feet, and Feet Per Second. Most of this window is "grayed out" because of other option choices you have made.
{__ } Move to the Position Filter tab. Make the Minimum Satellites "4 or more," for good 3-D fixes. Accept any PDOP. Include only positions that are differentially corrected, i.e., "Differential." The result should look like Figure 6—7.
{__ } Under Coordinate System, again use the current display coordinate system. Accept it after checking that it is U.S. State Plane, Kentucky North Zone 1601, NAD83 (Conus), coordinate units and altitude units in Survey Feet, and the Altitude reference as MSL. Plan to export only 2-D (XY) coordinates. If any of these display settings aren’t right, back out of Export and correct the settings under the main Options menu.
Figure 6-5. Defining the form of the data to be exported.
{__ } Leave the options under "ArcView Shapefile" blank. Since you have now set all seven tabs, click OK to bring back the Export window.
{_} Review the Export window. It should look like Figure 6—2.5
If not, click "Properties" and fix things.
{__ } Click OK in the Export window. If you are asked about overwriting existing files, answer "Yes." You should then get an Export Completed window that looks like Figure 6—8. Click on More Details and read the resulting file. Dismiss that window and close its parent window.
Figure 6-6. Defining the attributes to be exported.
{_} If you now look at the project toolbar of the Pathfinder Office window, where the project you are working on is named, you will see the amount of storage space left on the disk that contains that project. You will also see a file folder icon. Click on it and examine the project folder: _:\GPS2GIS\RIVER_AV. Now pounce on the Export folder. You should see files that constitute an ArcView theme as well as the information files generated during the exporting process.
Figure 6-7. Determining the types of data to be exported.
Posnpnt.dbf
Posnpnt.shp
Posnpnt.shx
If you don’t see at least these files (perhaps with slightly different names), something went wrong and you will have to figure out what it was.
{_} If you pounce on a .txt or .inf file probably a text editor (e.g., Wordpad or Notepad in Windows) will open showing the contents of the file. Examine the .inf and .txt files. Normally you don’t need these files but they can be helpful if something goes wrong. When you are sure that everything is okay, dismiss the project folder window and minimize the Pathfinder Office window.
