- SPECIAL REPORTS
- THE MAGAZINE
If you should happen to see an advertisement for a book titled “Be A GIS Expert in 21 Days,” in the current street vernacular, “Forget about it!” It isn’t going to happen. I suspect most of us didn’t become surveyors in 21 days. Acquiring another specialty can quite likely have a similar learning curve. The good news is that many of us have entered the Brave New World of GIS and discovered we already possess some of the necessary fundamental skills. What we need now is some refinement, some advancement and some organization. So, where can you obtain these improved skills?
This topic might well fill an entire issue, but for the purpose at hand a summary outline of the possibilities is a good first step.
Corporate Training is that which software developers and their authorized and certified trainers provide. This is the fastest method to get yourself “up and running” with GIS. On the downside it can be a bit pricey. These courses tend to be compressed and intensive. It is best suited for individuals who have an immediate and urgent need to acquire GIS software skills. It is less effective for “occasional” GIS software users because it lacks reinforcement.
The Academic approach exposes the student to both the theory and the technology associated with working in the field of GIS. The number of institutions offering degrees and certificates is rapidly expanding. But for the working surveyor the investment of time and effort required in this type of program can be inhibiting. This is arguably the best option for those individuals who plan to devote 50 percent or more of their workload to GIS activities. There is at least one online certification program available.
Self-Study Courses. These come in two versions, media with textbook and the online method. This approach is most effective for those people with already well-developed computer skills.
The RTM (Read The Manual) Method. This approach could be basically described as acquiring the software and installing it. Then read the manuals and go for it. Crude as this may sound, a surprisingly large number of individuals working in the GIS field have acquired at least some portion of their skill sets in this fashion. As with self-study courses, it is advisable to be an experienced computer user before opting for this choice.
User groups provide another excellent opportunity to acquire GIS knowledge. You can find out about them in the professional periodicals and on the Internet.
GIS Degrees?GIS is a relatively new field, and thus, formal educational opportunities specifically named Geographic Information Systems are rare. Only very recently have any Bachelor of Science Degrees in Geographic Information Science become obtainable. There are currently no legal requirements to practice in the field of GIS. So there are a variety of ways one gets involved in GIS work, surveying being one of them.
A good candidate for full-time GIS work might have a Bachelor of Science in Geography, an LS and an AS or equivalent in Computer Science. But as already pointed out, there are various levels of GIS use and a number of training and educational opportunities available to support most of them.
Basic GIS Survey ProjectFor this example, I am using a comma delimited .txt file with fields for Point number, Northing, Easting, Elevation and Description, an AutoCAD .dwg file and a .tif (tagged image file) of the same area. Any comparable data sets you may have will work for this exercise. Start the ArcView program.
Adding DataThere are several ways to add data to an ArcView project. The quickest and easiest is to add a theme. To add a “feature” or “image” theme we need to have a View Window open. Click on the Add Theme button. This is probably a good place to explain the difference between a Button and a Tool. A button causes an immediate action. In the case of the Add Theme button, it causes the navigator window to appear. A Tool awaits further action from the user. For example, the Zoom Tool requires the user to select the area to zoom to. Whereas the “Zoom to Selected” or “Zoom to Extents” buttons immediately execute the function.
A “Theme” is basically anything that can be viewed as a “layer” in ArcView. Most surveyors don’t typically work with Coverages, Shape Files or Geodatasets. We do much of our work with point files, aerial imagery and CAD files. So, let’s start out putting some typical survey data into ArcView.
We often start projects with coordinate files, some existing map or CAD files, and if we’re fortunate, some digital imagery. To put a coordinate file into ArcView, we use the “Table” document. To ArcView, a “Table” is an INFO file from ArcINFO, a .dbf file or a .txt file. Click on the Table document, then click the “Add” button. Make sure the “List File Type” box is set to the extension you will use. Then navigate to the file. Select the file and click “OK.” The file appears as a table.
Next, open the “View” window by clicking on the “View” document and selecting “Open” or “New.” On the top row of menus click on “View.” The third item down is “Add Event Theme.” This brings up the Event Theme dialog box. The name of your table should appear in the top box. The other two boxes are for “X Field” and “Y Field.” Using the down arrow, scroll down to the fields corresponding to X and Y in your table and click “OK.” The point file name should now appear in the table of contents. Check the box to the left of the title and the points should appear in the view.
Adding Image FilesImage data can be very helpful to surveyors. In the days before portable GPS units, which allow us to enter the positions of existing points and navigate to them, we needed to know where our survey points were in the “real world.” This was especially true if we had no previous knowledge of the points or area in question. To be in coincidence with feature data and survey point data, images need to be registered. Registering is the GIS term for defining the coordinate system for data. With image and scanned vector data this is most often accomplished by digitizing. The RMS (root mean square) error displayed by the program reflects the precision of the user’s skill and the accuracy of the media. For example, an aerial photograph with pre-marked photo control points with known coordinate values will normally yield better results than using a “photo ID” point with scaled coordinates.
Most readily available digital image data is already projected. It is also very difficult to re-project. To ensure that feature data will correctly overlay on image data they must be on a common system.
Overlaying survey points on photography is a common practice, and ArcView easily accommodates this. All that is needed is a digital ortho-rectified image projected on the same system as the coordinate file used.
To add imagery, the image type used must be checked in the “Extensions” menu. Then click the “Add Theme” button. We need to set the “Data Source Types” to “Image Data.” Navigate, select and click “OK.” Check the box and view. If you see the image but not your points, don’t panic. ArcView adds all new themes to the top of the Table of Contents. The “Draw Order” is from bottom to top. To change the draw order simply hold down the left mouse button on the theme you want to move and pull it up or down.
Adding CAD DataBefore CAD data can be used by ArcView, the CAD Reader Extension must be loaded. Click on the CAD Reader Extension. Click the “Add Theme” button. Navigate to the CAD files. Be sure to set the “Data Source Types” to “Feature Data.” Select one (or as many as you want by holding the shift key down) and click “OK.” Check the boxes for the CAD themes. (See Figure 1 on page 78.)
One of the strongest features of ArcView is its splendid online Help Library. It is both intuitive and comprehensive. The Help files can be accessed in three ways. Click on the Help Menu and select the “How To Get Help” option. You get a complete overview page with links. If you select the “Help Topics” option you get a dialog box with three tabs. If you choose the “Contents” tab you get a general outline of categories. If you click on the “Index” tab you get a search box that allows the user to type in a keyword to bring up an alphabetic listing of specific help items. The third tab is “Find,” which sets up a Windows library of specific keywords. There is also the Help Button (Arrow and ?). Clicking it prior to clicking on any tool or button automatically brings up a help screen. The F1 key is also a short cut to help screens. (Hint: if you are working this exercise and having trouble with anything, this is the section that tells you how to get help.)
There is one very important point to remember about all of the data entered into an ArcView project. None of the actual data resides in the project “apr” file. The project file saves only the path to the data. In AutoCAD terms, an ArcView project is very similar to an AutoCAD drawing file, which contains only external references. For the benefit of readers not familiar with AutoCAD, I will provide a brief explanation.
“The Holy Grail” in GIS is thought to be the seamless transition or marriage between CAD and GIS systems. When we begin to edit feature data in ArcView, the difference between CAD products and GIS products come into remarkably clear focus. Drafting capability in basic ArcView for instance is limited to the point of frustration for CAD users. Extensions can enhance the process of “linework” editing, but in this exercise we will only make an edit to the point file. We will cover lines and polygons in more depth in a future article. To view CAD data in 3D, the 3D Analyst Extension ($2,500) is necessary.
First, let’s look at the point table on page 80.
The sample data set in the graphic contains different types of survey points. So, to be able to show them with different symbols in the view, we need to add a field with a unique qualifier. First, to make the table editable, make it “active” by clicking on it in the Table of Contents. Then from the Theme menu choose “Convert To ShapeFile.” Follow the prompts to get the new shape file into the view. Then make it active. Click the “Open Theme Table” button. From the “Table” menu, choose “Add Field.” Enter “Order” in the name box and choose “String” as type. Click “OK.”
From the “Table” menu choose “Start Editing.” Select the “Edit Tool” (the arrow to the right of the Select Tool). Click in the first record of the “Order” field. “Populate” all the records in the field with the appropriate value. (I am arbitrarily using 1-4). Click “Stop Editing” from the “Table” menu and accept defaults. Close the table and open the view.
Make the point shape file active. Double-click on the legend. That brings up the legend editor. In the “Values” box choose “Order.” In the “Legend Type” box, scroll down to “Unique Value” and select it. In the “Color Schemes” box at the bottom of the Legend Editor choose a color scheme that contrasts well with your other data. Click “Apply” and close the Legend Editor. Your project may now look similar to Figure 3 on page 81.
In the next article we will look into the heart and soul of GIS: the data.