[VS 361 – Introduction to GIS]

[Centennial College Engineering Technology and Applied Science]

Geo-referencing a Raster data – (lab1)

Registering your map for the first time

You must always register your paper map/Aerial Photo before you begin digitizing from it. This involves establishing control points to register the Image to the geographic space of your GIS data. If your map has a grid or a set of known ground points, you can use these as your control points. Control points can also be saved to and loaded from x,y coordinates stored in a comma-delimited text file. In this lab, you are going to input the ground control points from the text file and create 3 points to geo-reference the image. In this exercise, the control points and their ground coordinates are identified for you on the Image.

Steps

  • Start ArcView
  • Select a NEW blank document.
  • Select Tools from the main tool bar and choose Add XY Data
  • Select Folder icon next to the First selection box (Choose a table from.....)

Then find the Digitizing txt from the location

  • Select Edit Button that locates in the lower right corner of the window
  • Choose Select>Geographic Coordinates>North America>N.A.D 83.prjand then clickAdd

ClickOk forall pop up Messages

You can see now three Control Points have been added to the map content.

  • Notice how the coordinates change in the lower right corner of the ArcGIS window whenever you move the mouse.
  • It is better to make Ground control Points (GCP) shapefile before adding the image.

Steps –

Right click the Digitizing points, Select Data, Export data, Navigate to the location

H:\VS361\Lab1 and Give the Name GCP.shp and click OK,

Once GCP points in the map content, remove the Digitizing point Event file from table of content

  • Click the GCP point and symbolize with Green colour and size 14

Important: Please give answers for all questions below

Questions

  1. What is the coordinate for each point - (3 marks)

Note: Move the mouse on each point and write down the coordinates for each point (See the status tool bar to get coordinates)

Now add Centennial_College.Jpeg image into Table of content

Steps:

  • Select the add Data button, it looks like a plus sign over a box.

Navigate the folders in the Add Theme box to display the working directory that contains your data H:\VS361\Lab1\Centennial_College.jpeg. You should now see a file named as Centennial_College.jpegin the display of the Add Theme box.

  • Select the Image and Click on Add button to add the image on the table of content
  • There will be a pop up message displaying “Coordinate Missing and can’t projected”, click OK/Add
  • Turn on the Georeferencing toolbar by clicking on ViewToolbarsGeoreferencing

Quesion:

  1. What is the Full Extent of the Aerial photo? (Coordinate values Latitude and Longitude. -2 marks– Move the mouse on top corner and take the coordinates from the status bar)

Top Left Corner =

Bottom Right Corner =

  • You can see now Control both points and the image are on the Map Content, but control points aren’t overlapped with place1, place2 and palce3.
  1. Why doesn’t this image overlap with control points? ( 1 mark)

Georeferencing the image

  • Begin by clicking the Add Control Points button

(Select a point on the image and match it to a point on the control layer when georeferencing images)

(Tip: Use the magnification window to avoid having to zoom in and out at

different extents. Click on Window?Magnifier)

  • First Select the Place 1 point on the image and then click on the nearest Control point
  • Next Select the place 2 point on the image and then click on the nearest Control point
  • Continue adding the control points until the desired level of accuracy has been achieved.

(The image will update automatically if Auto Adjust is enabled)

  • At anytime the attributes of each control point can be viewed by clicking on the ViewLink Table button. This dialogue shows the map coordinates of the source (XSource and Y Source) and destination points (X Map and Y Map). By double clickingon the X Map and Y Map, the destination coordinates can be altered if they are incorrect.Also, any control point can be deleted via the Link Table dialogue.

(Interpretation: Once threecontrol points have been added an RMS error can be calculated for each point.The RMS error measures the accuracy of the control points and can be used to findinaccurate entries. Frequently, major projects will require that the RMS error does notexceed half the pixel size. however, other projects will just try to minimize the amount oferror. Acceptable error levels depend on the accuracy required for the project and thedata being geo-referenced)

  • Once all the control points have been added the image must be updated and, if needed,rectified. From the toolbar click GeoreferencingUpdate Georeferencing to store thecontrol points. If this image is going to be re-used in ArcMap again, there is no need to be rectified the image imeediately. Once the image is added to ArcMap, it will be transformed onthe fly using the coordinates obtained from the control points. A permanenttransformation can be applied by Rectifying the image
  • To Rectify the image, click on GeoreferencingRectify and specify the Output pathand filename. Leave all other values as default
  • The image will be transformed and a new raster will be created in a TIFF file format
  1. What is the Full Extent of the Aerial Image after assigning the coordinates? (Coordinate values Latitude and Longitude) - (4 marks)

Top Left Corner =

Bottom Right Corner =

  1. What is the map Scale now? (1 mark)

Creating New Shapefiles

You can create new shapefiles and dBASE tables in ArcCatalog. When you create a new shapefile, you must define the types of features it will contain, whether those features will represent routes (m-values), and whether those features will be three-dimensional (z-values). These properties can't be modified after the shapefile has been created. You can also define the coordinate system of the shapefile. If you choose to define the shapefile coordinate system later, it will be classified as Unknown until then.

Procedure

For this task you need to launch ArcCatalog .

  1. Select H:\VS361\Lab1 folder in the Catalog tree.
  2. Click the File menu, point to New, and click Shapefile. (Figure1)
  3. Click in the Name text box and type a name for the new shapefile. (Figure2)
  4. Click the Feature Type drop-down arrow and click the type of geometry the shapefile will contain.
  5. Click Edit to define the shapefile's coordinate system.
  6. Select, import, or define a new coordinate system.
    It's highly recommended that you define the shapefile's coordinate system now; Click Edit button>Select>Geographic Coordinate>North America>N.A.D.83.prj
  7. Click OK.
  8. If the shapefile will store polylines representing routes, check Coordinates will contain M values. (For Roads Layer)
  9. Click OK.
    Please Create Parks (polygon), Roads (Polyline) and Address (Point) new shapefiles in the folder's contents (6 marks)

Figure 1Figure 2

Preparation for Digitizing

The editing tools in ArcMap make it easy to create new features. You use edit tasks, the edit sketch, sketch tools, and snapping to create new features in ArcMap. In this exercise, you will digitize a new polygon features, new polyline features and new point features into shapefile layers that you already created under H:\VS361\Lab1 directory.

You will begin by starting ArcMap and create a new map document, then add shapefile layers (Parks, Roads and Addresses) and the image that already been geo-referenced.

Note : Edit layers one at a time

-First add parks layer and complete the Editing – Remove layer from Table of Content after done

-Secondly Roads Layer and complete the editing – Remove after done

-Finally add Address layer and complete the editing- Remove after done

Digitizing Park polygons (10 marks)

  1. Click the Editor Toolbar button on the Standard toolbar to add the Editor toolbar to ArcMap.

Edit Tool

  1. Click the Editor menu and click Start Editing. If you only have one workspace in your map, you can start editing the map layers at this point. In this exercise, No workspaces are loaded in the map, so you don’t need to choose the workspace.

Setting the current task

Before you start digitizing a new feature, you must set thecurrent editing task to Create New Feature.

1. Click the Task drop-down arrow and click Create NewFeature.To create a new feature, you also need a target layer. Thetarget layer determines the type of feature you will createand in which layer it will be stored. Since there is only oneshapefile in the Map Content that you started to edit, the targetlayer is set to the Parks shapefile by default.

Using the Sketch tool

To create a new feature using the Create New Feature task, you must first create an edit sketch. An edit sketch is ashape that you draw by digitizing vertices using the sketchconstruction tools located on the tool palette.Several tools can add vertices to the sketch. You will usethe Sketch tool to add the study area polygon.

  1. Click the tool palette drop-down arrow and click the Sketch tool.

Sketch Tool

2. Click to add the first vertex of the sketch to the upper left corner of the Park in the image. The vertex should snap in place.

  1. Click to add the remaining vertices, snapping each vertex to a corner of the park in the Image. Create vertices clockwise until you completed the polygon. (Click 4 corners)

If you did any overshoot sketch, right click the mouse and select delete sketch.

Finishing the sketch

1. Press the F2 key or right-click and click Finish Sketch. This action adds the final sketch segment and creates the new feature.

Once you completed park polygon creation process, Select Save Edits option from Editor Tool bar, and then select Stop Editing to complete the process.

Adding Attributes - Use Attribute Table Document for create table

The new feature you created does not contain any attribute information. Because other polygon features are present in this shapefile, distinguish your new polygon from the others by adding descriptive information about it. You can add descriptive information for a selected featureusing the Attributes dialog box.

Click the Attributes button on the Editor Toolbar to add a description attribute to the new Parks polygon.

Next task is to add Attribute Fields to the Parks table.

  1. Right click the Parks layer locates in the Table of Content; choose open table option to view the table

Expand the Attribute table and click the Option button that locates at the bottom right corner of the Attribute table.

  1. Select Add Field option to add a field to the Park Layer
  2. Complete the information as of figure

Name=Type

Type=Text

Length=50 then OK

Adding information into the Park Attribute table

  • Select Editor tool and Choose Start Edit
  • Open the Park Attribute table and Select Type Field of Record number 1 (This records belongs to one of the park polygons and it now highlighted with blue frame).
  • Double click the type field and add required information

(Car Park Lot 1, Lot 2, Lot 3 and Lot 4, University Car park, Vegetation/General Park)

  • Add information for all polygons of the Park Layer, and select Edit Tool Save Editthen Stop Editing.

Creating a Polyline Shapefile (Roads) (10 marks)

  • Insert/Add Roads shapefile onto the Table of Content (from your Centennial Directory)
  • Select Editor>Starts Edit. Target should be Roads layer
  • Select again Editor>Snapping option (it will bring a new window for selecting snapping options)
  • Check off options should be as following figure.

Target = Roads

Vertex, Edge and End should be check off for Roads layer.

Edit sketch edges should check off

Select Editor>Option and check off Show snap tips option to display tips when Edges touch the intersection.

Next select Edit Toolbar then select Options and set the Snapping Tolerance to 10 pixels.

This tells ArcMap how close the features should be to “snap them together” Don’t set thistoo high or features will snap incorrectly to adjacent features.

  • Digitize Highway 401, Ellesmere Road, Military Trail, Morningside Avenue, Conlins Rd and Challenger Crt
  • Select Editor>Save Edits and the Stop Editing
  • Open the Roads Attribute table and Add new Fields, St_Name (Text ) ,Type (Text, Length 20), FR_LT, TO_LT,FR_RT,TO_RT (Number), UID (Number)

Note: Road Types = Highway, Major Road, Local Road

St_Name= Street name, FR_LT= From Left, TO_LT=To Left, UID=Unique ID

  • Update information of each feature/record in Roads layer (Follow the polygon feature update method)

Note: UID Field value starts from 1000 and add 1 for each record after (Like 1001, 1002, 1003 ect....)

Creating a point Shapefile (Address_Points)(10 marks)

Your will add 12 address points into this Address_Points layer

  • Select Editor>Starts Edit. Target should be Address_Points layer
  • Select roof top of Centennial College and Make a point (Number 755)
  • Select roof top of Petro Canada gas Station and Make a point (3094)
  • Create 5 points for 5 houses that are located in left side of Conlins Rd (Number 100,102,104,106,108)
  • Create 5 points for 5 houses that are located in right side of Challenger Crt ( 2,4,6,8,10)
  • Open Editor>Save Edit and Then Editor>Stop Editing
  • Open Attribute table of Address_Points and add following Attribute Fields

Type (Text, Length 20), FR_LT, TO_LT, FR_RT, TO_RT (Number), Street (Text, Length 30)

  • Update Attributes with necessary information corresponding to each record(point)

Note: make sure to assign geographic coordinate system for layers you created.

Topology Validation(Correction)(5 marks)

Note : When you done the topology, you have to show your results to Instructor to get 5 marks

A GIS topology is a set of rules and behaviours that model how points, lines, and polygons share coincident geometry. For example

Adjacent features, such as two counties, will have a common boundary between them. They "share" this edge.

The set of county polygons within each state must completely cover the state polygon and share edges with the state boundary

Why topology?

“Topology has long been a key GIS requirement for data management and integrity. In general, a topological data model represents spatial objects (point, line, and area features) as an underlying graph of topological primitives—nodes, faces, and edges. These primitives, together with their relationships to one another and to the features whose boundaries they represent, are defined by representing the feature geometries in a planar graph of topological elements”

About topology validation

  • Validating the topology involves the following processing:
  • Cracking and clustering of feature vertices to find features that share geometry (have common coordinates)
  • Running a set of integrity checks to identify any violations to the rules that have been defined for the topology
  • Creating an error log of potential topological errors in your feature dataset

Topology check in Road Shapefile

Using ArcMap

  1. Add the topology tool bar by selecting View>Tools>Topology

b. Start Editing by selecting Edit tool bar

c. Click the Map Topology button on the tool bar and place a check next to all lines (Roads)

d. Click the Topology edit tool. A single click on line will enable you to move the line asa whole. Double click to gain access to individual vertices to be moved.

e. Check the topology of Road lines by zoom in at the intersection. If under shoot lines or over shoot lines are there, it is required to be rectified those geometries to become validate to do analysis in the database.

Overshoot Undershoot

Bring the cursor at the intersecting point of roads segments, then click Map Topology (Cluster Tolerance) button and click OK to assign the cluster tolerance. Next click the Topology Edit tool and select each segment at a time. This shows you that three road segments are coincided at the same junction. (Topology Correct).