Lab 3. GIS Data Entry and Editing.
The goal:
To learn about the vector (arc/node) and raster data types entry and editing.Objective:
Create vector and raster datasets and visualize them.Software for the lab:
ARCINFO, ARCVIEW.Reading:
S.Aronoff. Geographic Information Systems:A Management Perspective. Chapter 4-5.NOTES!!!:
All ARCINFO commands are in bold. Before you follow instructions, please type them and see the syntax of the whole command. This will help you to understand your action better. After the lab is finished, make sure that you quit the program. Otherwise it will run on the background and slow down the network performance in the lab.IF YOU GET FRUSTRATED or MADE AN ERROR: RADICAL WAY:
If you have prompt: “Arcplot:” then type “quit” and leave “Arcplot:”. This will bring you to the prompt “Arc:” At this prompt type “lc”. Hit “Enter”. This command will show you all your cover-ages. Use command “kill <coverage-name> all” to get rid of the one that has to be redone. Start all over.
SOFT WAY:
If you have prompt: “Arcplot:” then type “oops”. Watch changes. “Oops” command will bring you one step back. It is similar to “Undo Edits” option. You can do it untill you “know where are you”. Then repeat your commands again. Maybe look at the “help” menu. Pay attention to various options associated with commands.
I. Digitizing From Hardcopies.
This lab does not use the digitizing tablet for the data entry. You will use ARCINFO module ARCEDIT that utilizes digitizing tablet as well as a keyboard to enter coordinates of your feature, create its geographical extension, fill with necessary information and store as a raw coverage. Then you will have to use ARCINFO command “build” to create topology. By the end you will have to add an attribute item.
Open “Unix command shell”. If you do not know what is it, ask system administrator. Create sub-directory in your home directory called “lab3” using command “mkdir lab3”. Move into this directory using command “cd lab3”.
Check yourself by typing command “pwd”. You should see the last sub-directory name “lab3”. Now you are ready to start your lab exercise.
The first exercise will consist of digitizing a lake from the planimetric image. Planimetric image is a scanned image from the hardcopy map. The name “planimetric” means that it is a “plane” i.e. flat and does not have any reference to the curvature of the earth surface. This is very common map product.
The image is located in:
“/usr/manhattan/gis_class/yxg/data/plan56.tif”
Start ARCINFO software using menue option “Arcinfo” in “Apps” toolchest menu (upper left corner of the monitor).
Describe the image “plan56.tif” to find out its extent. You will need to find the minimum and maximum extent of this dataset for the digitizing process. Use ARCINFO command “describe”. Do not forget that image is in /usr/manhattan/gis_class/yxg/data. Therefore, give the whole path to the image.
Record your Xmin,Xmax, Ymin and Ymax values.
Start ARCEDIT module by typing the following command: Arc: arcedit
Now create a graphic canvas for the display of your future map features: Arcedit: display 9999
You should see the black graphic canvas on your screen. Place it conveniently. Pass control of the coordinates entry to your keyboard via the following command: Arcedit: coordinate keyboard
Now create the first dataset that will describe geographical area of your future data - tic marks: Arcedit: create tic56
Enter tic-Id numbers that would describe the 4 corners of your future coverage. Take numbers from the output of your command “Describe /usr/manhattan/gis_class/yxg/data/plan56.tif” in pre-vious step. Calculate the initial boundary as: Xmin - 500, Ymin - 500, Xmax + 500, Ymax + 500.
After you finished you should see something similar to the following line: The edit coverage is now /PROJECTS/YURI/TRAINING/EDITING/TIC56 WARNING the Map extent is not defined
Defaulting the map extent to the BND of /PROJECTS/YURI/TRAINING/EDITING/TIC56 Save your work by typing at arcedit prompt “save”. Good luck!
Arcedit: save
Saving changes for /PROJECTS/YURI/TRAINING/EDITING/TIC56 BND replaced into /PROJECTS/YURI/TRAINING/EDITING/TIC56 This comand saves all your work with data within the ARCEDIT module.
Each time you want to draw something within ARCEDIT , you have to specify your “drawing environments”. Type command “drawenvironment” and hit “Enter” button. You will see a lot of options. Now, draw on the canvas the TICs for your future dataset using the following options with the “drawenvironment” command:
Arcedit: drawenvironment tic ids (You can also do the shortcut: Arcedit: de tic ids ) Arcedit: draw
You should see on your graphic display the four TIC points that you have entered and their ID numbers.
Now let’s create the future dataset that will have a geographic extension of the file “tic56” that you are already created, using the following command:
Arcedit: create lake56 tic56
Creating /PROJECTS/YURI/TRAINING/EDITING/LAKE56
This command created a new dataset called “lake56” using geographical extension data from the dataset “tic56”. “Tic56” coverage serves only one purpose - to pass information about the coordi-nate system of your future data and its units.
The edit coverage is now /PROJECTS/YURI/TRAINING/EDITING/LAKE56
Let’s draw on the background image file “plan56.tif”. The following command will do it: Arcedit: image /usr/manhattan/gis_class/yxg/data/plan56.tif transparent 1
Arcedit: draw
You should see the black and white version of the “plan56.tif” image. If you like different color, change the last option in your command like this (for green) :
Arcedit: image /usr/manhattan/gis_class/yxg/data/plan56.tif transparent green Arcedit: draw
Because we do not digitize data from the hardcopy map we are not planning to estimate our RMS error. Our error of digitizing will depend on our zoom to the image. Please find the feature “Lake Carmel” on the screen. It should be located somewhere north-east from the center of the image. You can use “Pan” and “Extent” options om the upper left corner menu of your canvas. The menu is called “Pan/Zoom”.
Let’s make sure that our coordinates will be entered via the mouse. To do this type the following:
Arcedit: coordinate mouse
Now you are ready to create your own dataset with the outline of the Lake Carmel. Specify the features you want to digitize (in this case “arcs”, since you need an outline) : Arcedit: editfeature arcs (You can do also a shortcut: Arcedit: ed arcs )
You will see the following response: 0 element(s) for edit feature ARCS Coverage has no COGO attributes
You have 0 elements because your dataset does not have any features. You have to “add” them: To make sure that the software enables drawing of arcs type the following:
Arcedit: drawenvironment arcs (Or use the shortcut Arcedit: de arcs)
Let’s add them by digitizing the outline of the Carmel Lake. Arcedit: add
You will see the following menu:
1) Vertex 2) Node 3) Curve 4) Delete vertex 5) Delete arc 6) Spline on/off 7) Square on/off 8) Digitizing Options 9) Quit
Remember that you have to start any vector feature with the node. Then you can continue with the vertex and close your digitizing with another node. In case of polygon digitizing your nodes should be digitized at the same location as close to each other as possible. Use numbers on your keyboard to start your node, vertex or delete vertex, etc., corresponding to the numbers from Options above.
To digitize Lake Carmel outline from the dataset, start from any place. Just remember its location. You can do digitizing and simultaneously “pan” your image to digitize at the same resolution. If you will use various “Zooms” you will not digitize at the same resolution. You can digitize this dataset using only 2 nodes, but if you want to practice, use few nodes. To finish digitizing, hit 9 on your keyboard. To start again, use command “add” as before. If you make mistake, hit “9” key and type at Arcedit prompt command “oops”.
When finish digitizing, save your dataset using command “save”. You will see the following: Arcedit: save
Saving changes for /PROJECTS/YURI/TRAINING/EDITING/ROAD56 Saving arcs...
2 arc(s) written to /PROJECTS/YURI/TRAINING/EDITING/ROAD56 from the original 0, 2 added and 0 deleted
Reopening arcs... Saving tics...
** NOTE ** Tic(s) unchanged Reopening tics...
BND replaced into /PROJECTS/YURI/TRAINING/EDITING/ROAD56 Re-establishing edit feature ARC
Coverage has no COGO attributes
Now, remove your image (in real world you would remove the hardcopy map from the digitizing tablet) using commands:
Arcedit: image off Arcedit: draw
You will see only outline of the lake. Let’s check if you have any “dangle” nodes. The following command set your software to display all nodes:
Arcedit: drawenvironment node dangle
Let’s assign to the dangle node red color for better visualization: Arcedit: nodecolor dangle red
Now, redraw your data: Arcedit: draw
nodes. Otherwise you should see the red colored square where you nodes are “hanging”.
Zoom in really close. See the gap between two nodes ? Now it is time to correct this error. Use the command “nodesnap” to set up the threshold values for your editing. You will have to specify the radius within which your editing will work. The following command basically means: “I want my nodes being snapped within the distance that I will define using a circle, and any first node within this distance should be snapped (i.e. connected) ”.
Arcedit: nodesnap first * Define the tolerance circle Enter the center
Enter the edge
Now change your editing mode from “arcs” to “node”: Arcedit: editf node
Use ARCEDIT command “move” to connect (or “snap”) your nodes together. When prompted, click on the node, then hit the keyboard number 4 (move) and then select the second node with your mouse pointer. You should see how node will be moved and conncted with another one. Instead of the red square you will see white romb. This means that your nodes snapped succes-fully and instead of “dangling” nodes you created “pseudo-node”.
Arcedit: move
Point to the node to move <9 to Quit> Enter point
Node (610944.812,4589545.000) selected 1 = Select 2 = Next 3 = Who 4 = Move 9 = Quit
Save your work using command “Save”.
Remove image from the background using command “image off”: Arcedit: image off
Redraw your graphics: Arcedit: draw
Now you should see the black canvas and the white outline of the Carmel Lake. As you can see it is just outline. Now we have to add a label point to this dataset.
To do this, change editing mode in the software to start editing/adding label points (remember, we are dealing with the polygon!). Use the following commands:
Arcedit: editf label
0 element(s) for edit feature LABEL
You have 0 elements because you do not have labels yet. Add the label for the polygon using the following command: Arcedit: add
1) Add Label 5) Delete last label 8) Digitizing Options 9) Quit
Place your mouse pointer in the middle of the Lake Carmel and hit key 1 on your keyboard or click with the left button of the mouse. You will see yellow cross mark appearing on the screen. Hit 9 key on your keyboard to stop the editing process.
Now you have a typical polygon dataset within an arc/node structure. While you are in a label editing mode you can view the attribute table of your newly created node using command “list”: Arcedit: list
Record 1
As you can see the label has only one attribute - ID# = 1. It does not have any other attributes because we have not build our topology yet and the software does not know what kind of attribute table to use i.e. point, line or polygon.
To build topology we have to quit ARCEDIT module using the following command: Arcedit: quit
Keep all edit changes (Y/N) : y
This will replace all changes back into the original coverage(s) and/or INFO file(s) Do you really want to do this (Y/N) : y
Saving changes for /PROJECTS/YURI/TRAINING/EDITING/ROAD56 Saving arcs...
** NOTE ** Arc(s) unchanged Saving labels...
** NOTE ** Label(s) unchanged Saving tics...
Saving set tolerances to TOL file... Leaving ARCEDIT...
Arc:
Now you are back to the ARC module. ARC module is familiar to you from the previous lab. Use command “lc” to view your newly created coverage “lake56”.
Arc: lc
Workspace: /PROJECTS/YURI/TRAINING/EDITING Available Coverages
LAKE56 TIC56 Arc:
You should see in your workspace two coverages: “lake56” and “tic56”. Now build topology: Arc: build lake56 poly
Building polygons...
Let’s list the attribute table using the following command: Arc: list lake56.pat
How do we call this file ? What does it store ? Send me e-mail.
You should see such attributes as lake56# and ID#, Area and Perimeter. These are automatically created attributes that software produces for you as soon as you build topology. In case of lines you would see Length, etc.
Now you should have your lake56 coverage set as a polygon coverage with appropriate label. Next step will be attribute table update. You can do this from ARC module using command “additem”:
Arc: additem
Usage: ADDITEM <in_info_file> <out_info_file> <item_name> <item_width> <output_width> <item_type> {decimal_places} {start_item}
In our case we’ll issue command with the following options: Arc: additem lake56.pat lake56.pat name 30 30 C
Adding name to lake56.pat to produce lake56.pat. Arc:
This command added an item (feature attribute) called “name” having width of 30 characters. Capital letter “C” means that the item is set up as a character based. Other options might include integer or floating numbers with various decimal places.
Let’s list the attribute table using the following command: Arc: list lake56.pat
You will see regular attributes such as AREA, ID#, etc., and also your own attribute “NAME” that will have a blank line next to it. This is because we have not assign a value to this attribute. Let’s assign value “Lake Carmel” to it. We’ll do this in our next Lab4 after closer look at the attribute table editing.
Make a list of all commands you used and classify them into two categories:
1. Management of graphic elements and computer settings.
2. GIS database construction.
Send me e-mail with all answers.
II. Survey data entry in GIS.
Survey data are usually flat files that store geographical information and description of the feature that was surveyed. Survey can be done using automated data collection, such as Global Positioning System or manual - theodolite, line, etc.
For this exercise use ARCVIEW software.
We will have to import a flat file that was created by surveying USGS gauge stations (remember Lab2!) into ARCVIEW . You are given this file and asked to create a GIS dataset.
Close any other software you use.
Start ARCVIEW (look in “Apps” upper left corner of the monitor). Save your project as “lab3.apr”.
Open new View.
Set up your View properties as following: Call the view “USGS Monitoring Sites”. Map Units - meters.
Distance Units - meters.
Click on the icon “Tables” within your project window. Using “Add” button add a table “usgs.txt” from:
/usr/manhattan/gis_class/data View it.
As you can see this table has three columns: X,Y,Site. X,Y fields store coordinates, while Site has unique identification number for each USGS monitoring gauge.
Make your view “USGS Monitoring Sites” active and add the table “usgs.txt” to the view using the sequence of menues: View ---> Add Event Theme.
Select table “usgs.txt”. You should see that X field has X value and Y field has Y value. This hap-pened because fields in the table were named as X and Y. If you would have more complex table, you would be able to select the fields storing X and Y coordinates yourself.
Click “OK” button and you will see how in your view “USGS Monitoring Sites” a new theme appeared with the name “usgs.txt”. Make it visible and assign the red filled circle as a symbol. Save this project and send me e-mail that you finished.
