Lab 2 - 1 OnScreen Digitizing

8/3/2019 Lab 2 - 1 OnScreen Digitizing

http://slidepdf.com/reader/full/lab-2-1-onscreen-digitizing 1/10

Kursus GIS dan Remote Sensing

19-29 Nov 2007

DATA PREPARATION IN ARCGIS 9.X

(ON-SCREEN DIGITIZING)

SECTION 1

INTRODUCTION

There are two ways in performing on screen digitizing; on ArcMap and on Arc Tools

(Arc Info Workstation). Both results are compatible with each other. However, some

restrictions might need to be considered and taken into account.

OBJECTIVE

This practical will open up participant’s capabilities in trying GIS software rather thanthe conventional AutoCAD in doing digitizing. (Not that AutoCAD is not good!). By

using the most current GIS software, it is hope that by the end of this practical,

participant will be familiar with the software and be able to do an on screen digitizing

work.

Before starting the digitizing work, we need the map to be digitized placed as a digital

format. This digital map is known as the base map or the background mapping. This map

could be in any raster image format. (.pcx, bmp, jpg…..).

Q1. What about vector format?

METHODOLOGY

We have been given one image in . jpg format ( H_Langat.jpg) and one text file

(CtrlPt.txt) as the starting point. First open the image file in Arc Map, observe the

image and identify the potential features for digitizing.

For example, the potential layers:

1. Contour

2. Roads

Siti Aekbal Salleh

JSUG, UiTM 1




19-29 Nov 2007

3. Rivers

4. Building

5. Land use, water bodies (polygon)

Then, open Arc Catalogue and follow the instructions below:

1. Right click on your own folder or space choose ‘new’ and ‘Personal

Geodatabase’.

2. Specify name to your Personal Geodatabase, and then create new feature datasets.

3. Specify name to your Feature Dataset and assign the coordinate system and X

and Y domain, and then create new feature classes.

Siti Aekbal Salleh

JSUG, UiTM 2




19-29 Nov 2007

1.0 IMAGE REGISTRATION

Now that we have already managed our Geodatabase, we need to proceed on the image

registration. Check back the .txt file that is provided. Open Arc Map and follow the

instruction accordingly.

1. Right click on the empty view and go to Properties. Define the coordinate system.

Then check the Data Frame info.

Siti Aekbal Salleh

JSUG, UiTM 3




19-29 Nov 2007

The coordinates system for the working space is defined and at real below of the view on

the right hand side we can see that the unit is in meters.

2. Then, click on Tools and choose Add XY data. Choose the .txt file that represent

the control points of the image file and then assigned the coordinate system.

3. Then, display the H_Langat.jpg. If the image is not displayed, click on the

Georeferencing and choose Fit to Display.

4. Then, click on add control point , start registering the image to the reference

coordinate of control points. Click at update georeferencing and Rectify the new

image.

5. To maintain the properties of the control points we have to convert the .txt file to

geodatabase, so that it will be compatible at any session of working. So, right click at

the CtrlPt.txt event and choose Data and Export Data. The control points will now

be appearing in the .shp.

Siti Aekbal Salleh

JSUG, UiTM 4




19-29 Nov 2007

ADDING ATTRIBUTE DATA

OBJECTIVE

In this practical session, you will be introduce to the steps involves in getting the attribute

into spatial data using ArcGIS software. At the end of this session, you are expected to

have the ability to input the attribute data into any of GIS software package.

INTRODUCTION

There are many approach can be use to add attribute data into GIS. The very simple and

straightforward process is by entering directly into ArcMap. Arc Catalogue on the other

hands enables you to construct your attribute tables while you create your feature classes.

In some cases, you might already have the attribute data in different file format such as

Access, Excel, Dbase, etc (sometimes it call external database). It is waste of time to

enter all the data again in GIS software. Here, what you can do is to join or relate external

database that you have with standard attribute table in ArcMap. However, the main

requirement is to have common identifier or key in both of data.

1. Adding attribute data directly using ArcMap

The data that you have digitized in your previous session will be used in this session.

a) Adding fields to the layer

Open ArcMap

Add a new layer by clicking Add Data

Right-click the layer and click Open Attribute Table

Click the Options button on the table and click Add Field

Siti Aekbal Salleh

JSUG, UiTM 6




19-29 Nov 2007

The add field dialog box appears

Name: The name for a new field

Type: Types of field for example Text, Short Integer, Long Integer, Date etc.

Field properties: The length or precision of field

Click OK and you can find a new field in the attribute table

You can add any new fields in your table in the same manner.

a) Adding attribute values to the new field

To add a new attribute values or records, click the Editor toolbar button

Click Editor Toolbar and Start Editing

Right-click on the layer and click Open Attribute Table

Now, you can enter a new attribute values or records in the new fields

Siti Aekbal Salleh

JSUG, UiTM 7




19-29 Nov 2007

2. Adding fields from Arc Catalogue

In Arc Catalogue, we are able to compose the attribute table fields and their properties.

After you created the feature classes, right click on the feature class you want to

edit the attribute table and click on properties. Now you will see this dialogue

box:

At the Fields option just types the field name that you want to add. Note that you

have to make sure you choose the right geometry properties for each added fields.

This is important in order to avoid problem when you adding the attributes to the

fields created. The value entered must match the specified geometry properties.

3. Joining external attribute table in ArcMap

a) Adding external attribute table

Click Add Data and add the database that you wish to join or relates

You will see your attribute table has been added into Layers tree

Siti Aekbal Salleh

JSUG, UiTM 8




19-29 Nov 2007

Right click / Open Attribute Table to view the data

b) Joining attribute table

Right click on the layer / Join and Relates / Join…

The Join Data window appears

Want do you want to join to this layer? : Join attributes from a table

Choose the field in this layer that the join will be based on: Select the common

identifier field in this layer.

Choose the table to join to this layer, or load the table from disk: The name of the

external database.

Choose the field in the table to base the join on: Select the common identifier field

in the external database. Click OK, and both of the table will be joined together

Siti Aekbal Salleh

JSUG, UiTM 9




19-29 Nov 2007

GOOD LUCK AND HAPPY TRYING!!!

Siti Aekbal Salleh

JSUG, UiTM 10

Lab 2 - 1 OnScreen Digitizing

Documents

Transcript of Lab 2 - 1 OnScreen Digitizing