PROJECT 6b-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 C111315 A.COR. In this project you will make and display an ESRI point coverage from the COR file, using the Trimble software and ArcInfo.
{__ } Start Pathfinder Office in the usual way.
{__} You should find a differentially corrected file C111315A.COR in your project’s main folder. Open C111315A.COR in Pathfinder Office. Map and timeline it.
{__ } Under Pathfinder Office Options set the Distance Units to "US Survey Feet."8 Make the other distance variables 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 the Altitude Units U.S. Survey Feet.
{_} Don’t change anything in Style of Display unless the Coordinate Order is not North/East. The Time Zone should be Eastern Standard USA. The image you see should look something like a fishhook—in keeping with our nautical theme; the GPS track was taken over about 45 minutes starting around 10:00 A.M.
The process of making an ArcInfo coverage 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 six major facets to the Export Setup file. In no particular order, they are:
• Data
• Output
• Attributes
• Units
• Position Filter
• Coordinate System
{__ } Bring up the Export window, by either picking Export under the Utilities menu item or by clicking on the Export icon on the Utilities tool bar. In the window (see Figure 6—14) "Browse" to find C111315A.COR in_:\GPS2GIS\RIVER_Al. Select it, then "Open" it.
{__ } The chore now is to pick a folder that will hold the exported coverage. If you’ve set up the project correctly the default folder shown should be_:\GPS2GIS\RIVER_Al\EXPORT.
{__ } The next task is to choose a "Sample" export file from which you can tailor one that completely suits your needs.) Don’t modify theSample.
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
If you are planning to use either a UNIX workstation version of ArcInfo or ArcInfo running under Windows NT on a PC, you want to choose the UNIX Setup. Only if you are running PC Arcinfo or ArcCad do you want the PC setup.
{__ } Choose either the "Sample ARC/INFO (UNIX) Generate Setup" or the "Sample ARC/INFO (PC) Generate Setup," as appropriate, from the drop down list. Then click "New." A window named New Setup will appear. (See Figure 6—15, which illustrates the UNIX or NT setup.) Choose "Copy of existing setup." A Setup Name such as "Copy of…" will appear in the text box. In that text box rename the setup to AI_yis# 1. OK the window.
{_} A window should appear9 entitled Export Setup Properties—
AI_yis#1. The top portions should look like Figure 6—16. In this window are six tabs, conforming to the list of six facets listed above.
{_} 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. Make the Starting Feature ID 501 (this will become the first value of the cover-ID number); set it up so each session will begin with this value. See Figure 6—17.
{__ } 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."
Figure 6-14. Exporting a GPS data file to a GIS format.
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, pick UNIX Files for workstation ArcInfo, Windows Files for Windows NT ArcInfo, or DOS Files for PC ArcInfo, depending on where the output of the export process is headed.
{__ } Under the Attributes tab, let’s export a couple of attributes both to illustrate how it’s done and so our Point Attribute Table (PAT) won’t be so dull. Make checks by Time Recorded (under "All Feature Types") and Height (under "Point Features") as in Figure 6—18.
Figure 6-15. Creating a customized setup to make a coverage.
Figure 6-16. Set six properties for a successful ArcInfo export.
{__ } The Units tab: Here you will tell Pathfinder Office to use the Current Display settings, which should be U.S. Survey Feet, Square Feet, and Feet Per Second. You won’t be concerned with most of the other fields here because you aren’t using Latitude and Longitude. So accept the default values.
{__ } 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—19.
{__ } Under Coordinate System, use the current display coordinate system. Accept it after checking that it is U.S. State Plane 1983, Kentucky North Zone 1601, NAD 1983 (Conus), coordinate units in Survey Feet, with the altitude units in (International) Feet and that the Altitude reference is 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 Options menu. Since you have now set all six tabs, click OK to bring back the Export window.
{_} Review the Export window. It should look like Figure 6—14.
If not, click "Properties" and fix things.
Figure 6-17. Defining the form of the data to be exported.
{__ } Click OK in the Export window. If you are asked about overwriting existing files, answer "Yes." You should get an Export Completed window that looks like Figure 6—20. Click on More Details and read the resulting file. Dismiss that window and close its parent window.
{_} If you now look at the project toolbar of the Pathfinder Office window, where the project on which you are working is named, you will see the amount of storage space left on the disk that contains the project. You will also see a file folder icon. Click on it and examine the project folder: __:\GPS2GIS\RIVER_AI. Now pounce on the Export folder. You should see the files we discussed earlier— POSNPNT.AML, and so on. If not, something went wrong and you have to figure out what it was.
Figure 6-18. Defining the attributes to be exported.
{_} If you pounce on a .txt or .inf file a text editor (e.g., Wordpad or Notepad in Windows) will probably 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.
See the Converted File in ArcInfo
Start up ArcInfo. Don’t forget to type &STATION 9999 or whatever it takes to set the display device and terminal. Using the WORKSPACE command, change to the directory _:\GPS2GIS\RIVER_AI\EXPORT An adjustment to the AML may be necessary to make it work properly. Modify the POSNPNT.AML in a text editor such as WordPad or NotePad as follows:
Figure 6-19. Determining the types of data to be exported.
Rewrite:
ADD FROM POSNPNT.PA
So it reads:
ADD FROM ..\POSNPNT.PA
Save the file and close the editor.
{__} Execute the AML by typing &RUN POSNPNT.AML. When it finishes you should be able to list the coverages (LC in NT or UNIX; LISTCOVS in PC) and see the coverage POSNPNT.
{__} Now list the Point Attribute Table (PAT): Type LIST POSNPNT.PAT. A portion of the table is shown in Figure 6—21. Here you should see the identifying items as well as the time each point was taken and the height above sea level of the fix. The first point should have a POSNPNT-ID of 501. Note the beginning and ending time for the data collection run. Note the wide variation of altitudes; since the river is very placid and almost level, this gives you an idea of what you can expect in the way of vertical accuracy for individual fixes—even those that have been differentially corrected. True, this is a file taken with older equipment and differentially corrected with older software—and things have improved—but you still wouldn’t want to be on an airliner whose altitude was being determined by GPS solely.
Figure 6-20. Results of a successful export process.
{__ } If you want the X and Y coordinates in the table, you can execute the command: ADDXY POSNPNT POINT. List the PAT again. The coordinates you added are the state plane coordinates in feet.
{__} Look at the POSNPNT coverage itself: Go into ARCPLOT (command alias: AP). Make the ARCPLOT window fairly large. Type:11 MAPEXTENT POSNPNT TICS POSNPNT POINTS POSNPNT POINTTEXT POSNPNT POSNPNT-ID {__ } You should see the same GPS track that you saw before. Each point is numbered. Zoom up on the west end of the GPS track to see the identifying numbers clearly. (See Figure 6—22.) (Use MAPE *, make a box, CLEAR, and redo the POINTS and POINTTEXT commands above.) You should be satisfied that you have turned a GPS COR file into an ArcInfo point coverage of 83 points. Stay in ARCPLOT.
Figure 6-21. Point Attribute Table (PAT) from the export process.
