Tutorial 2: Digital Elevation Model

Create a Digital Elevation Model (DEM) from contours and point data using ArcGIS 10.x

Is any digital representation of the continuous variation of elevation over space. The DEM is a computer representation of the earth's surface, and as such, provides a base data set from which topographic parameters can be digitally generated. Through the use of ArcMap, provided that we have elevation data in the form of points or contours, we can manage to create a DEM. DEM data is usually in a raster format. To create a DEM, we use the Topo to raster tool. The Topo to raster tool can be accessed through ArcToolbox => Raster Interpolation => Topo to raster as shown in figure 1 below.

Figure 1: Topo to raster

After the Topo to raster tool has been opened, we will be provided with the screen as shown by figure 2 below.

Figure 2: Topo to raster

After we have completed setting up the required information as shown by figure 1 above and clicked the OK button, ArcMap will create the Digital Elevation Model for us. The produced raster will look like the one shown by figure 3 below.

Figure 3: Created DEM

The created DEM data can be previewed in Arc Scene in a 3D form. To do so, we will open the data in Arc Scene as shown in figure 4 below.

Figure 4: Previewing the DEM data in Arc Scene

When the DEM is added to Arc Scene, it would normally be displayed as a flat document as shown in figure 4 above. It view it in an elevated form, we will have to right click the DEM data on the scene layers shown in figure 4 above and thereafter go to properties as shown in figure 5 below.

Figure 5: Previewing the DEM on Arc Scene

After we have clicked on the properties option illustrated in figure 5, we will thereafter be provided with the screen as shown in figure 6 below.

Figure 6: Layer properties

We will set the elevation from surface as floating on custom surface and make sure that our DEM data has been specified, the next step is to specify the factor to convert layer elevation to scene units. We will set this option to custom and give it a value of 2 as shown in figure 6 above. We will complete by clicking on the OK button. After we have completed the step illustrated in figure 6 above, the elevation data will be displayed as shown in figure 7 below.

Figure 7: Displaying the DEM data in a 3D model

We can also use Arc Scene to have a 3D preview of the building of the area. This can be done by opening the layer in Arc Scene. After the layer has been added in Arc Scene, it will be displayed as illustrated by figure 8 below.

Figure 8: Previewing the buildings on Arc Scene

To have a 3D view of the data, we will again access the properties of the data as it has been illustrated by figure 5 above. After we have accessed the property window of the data, we will be provided with a screen as illustrated by figure 9 below.

Figure 9: Properties window for the buildings layer

After we have opened the expression builder, we will be provided with the expression builder and it will be displayed as shown in figure 10 below.

Figure 10: Expression builder

Using the expression builder, we will add three to the number of floors and multiply by three and thereafter click on the OK button to perform the expression and thereafter click on the OK button. The buildings will thereafter be displayed in a 3D form as shown in figure 11 below.

Figure 11: Buildings displayed in 3D

To preview the buildings in an elevated surface using the DEM data, we will access the properties of the buildings layer, and thereafter go to the base heights of the layer and set the DEM layer as the source of the base heights as shown by figure 12 below.

Figure 12: Setting the base heights

After the DEM data has been selected, we will click the OK button. The buildings will thereafter be displayed as shown in figure 13 below.

Figure 13: 3D model of the buildings

Using the same procedures, we will add the rest of the layers and the data will be displayed as shown in figure 14 below.

Tutorial 1: Google Earth Imagery Geo-refrerencing tutorial using ArcGIS 10.x

This tutorial guides you through the process of how you can use ArcGIS's Geo-referencing toolbox to geo-reference a map or any aerial imagery available in hand.

GEOREFERENCING
Geo-referencing refers to aligning geographic data to a known coordinate system so it can be viewed, queried, and analysed with other geographic data. Geo-referencing may involve shifting, rotating, scaling, skewing, and in some cases warping, rubber sheeting the data. Geo-referencing can be done using ArcMap. Before we perform geo-referencing, we will obtain an image from Google Earth and thereafter geo-reference the image in ArcMap.

SETTING THE COORDINATE SYSTEM AND THE UNIT OF MEASUREMENT IN GOOGLE EARTH

To set the coordinate system and the unit of measurement in Google Earth we have to go to Tools => Options as it has been shown by figure 1 below.


Figure 1: Setting the coordinate system and unit of measurements

After we have clicked the "Options" option, we will be provided with the screen shown by figure 2 below. To complete the settings, we will click on OK.

Figure 2: Setting the coordinate system and unit of measurements

Viewing grids on Google Earth

To view grids on Google Earth, we will go to View => Grid as it has been shown by figure 3 below.

Figure 3: Viewing grids

After the grids have been enabled, we will be able to see the zone we are working on in the coordinated system that is being used. In this case the UTM coordinate system. We will select the Universal Transverse Mercator (UTM) coordinate system. We will set the units of measurement as Meters, Kilometers.

Adding Place Marks
Before we add the place marks for georeferencing, we have to tilt and compass the area that we are going to place the place marks. To tilt and compass, we will go to View => Reset => Tilt and Compass as it has been shown in figure 4 below.

Figure 4: Tilt and Compass

To add place marks of an area in google earth, we will go to Places => Add => Place Mark as it has been shown in figure 5 below.

Figure 5: Adding place marks

We will place the place holders on google earth and thereafter record the coordinates of the place holders. Figure 6 shows the place holders placed on google earth.

Figure 6: Place holders on google earth

After the place holders have been created. We will save the google maps screen as an image. To save it, we will go to Save => Save image as it is shown in figure 7 below.

Figure 7: Saving the image with place holders

After the image has been saved. We will open it in ArcMap. To load the image in ArcMap, we will set up the folder connections of so as to allow the image to be added as data. When we load the data into ArcMap, we will get the message that the data being loaded is lacking a special reference as it is shown in figure 8 below. This is because the data is loaded as a normal image without a defined coordinate system. We will click the OK button an proceed.

Figure 8: Unknown spatial reference

After the image has been loaded on ArcMap, the next step is to open the georeferencing toolbar. In order for us to open this toolbar, we will go to Customize => Toolbars => Georeferencing as shown in figure 9 below

Figure 9: Accessing the georeferencing toolbar

After we have enabled the georeferencing toolbar, the toolbar will be visible, and by using it, we

will manage to georeferenced the image. Figure 10 shows the georeferencing toolbar of ArcMap 10.x and its respective controls.

Figure 10: Georeferencing toolbar

To start georeferencing the image, we will click the add control points button. After we have

clicked the button, the pointer of the mouse will change its shape to a plus sign. We will therefore

have to click a point on the image and thereafter specify the coordinates of the point. The coordinates that we will use in the performing of geo-referencing are the ones that we obtained from the control points that we placed on Google Earth. To place a control point on an area of the image, we will have to zoom to the control point of the image, thereafter go to the georeferencing toolbar and click the add control points button, thereafter right click and go to input X and Y data as it is shown in figure 11 below.

Figure 11: Adding control points

After we have clicked the Input X and Y … button, we will be provided with an input box which will allow us to insert the X and Y coordinates of the point as shown in figure 12 below. This process will be repeated until when all control points have been finished.

Figure 12: Entering coordinates

ArcMap as well allows us to view the error that occurs as a result of georeferencing. This error can be viewed through the link table in the georeferencing toolbar. Figure 13 shows the link table used in this project.

Figure 13: Link Table

After we have finished inserting the coordinates of all control points, we will go to the georeferencing toolbar and rectify the Geoprocessing process as it is shown by figure 14, below.

Figure 14: Rectify

After we have clicked the rectify option, we will be provided with a screen which will allow us to save the georeferenced image. Figure 15 shows the screen.

Figure 15: Saving the georeferenced image

After we have finished saving the georeferenced image. We will remove the image from ArcMap and thereafter open ArcCatalog in order to specify the coordinate system used in the georeferencing process.

SPECIFYING THE COORDINATE SYSTEM

To specify the coordinate system used, we will have to right click the layer in ArcCatalog => Properties as shown in figure 16 below.

Figure 16: Specifying the coordinate system

After we have clicked on the properties option, we will be provided with the raster dataset properties as shown in figure 17 below.

Figure 17: Raster dataset properties

To specify the spatial reference of the data, we will click on the edit button. In the case of this project, the settings will be made as illustrated by figure 18 below.

Figure 18: Specifying the coordinate system of the file

We will finish the process by clicking the OK button and thereafter the apply button.