Lecture ERS 120: Principles of GIS - Practice 6: Advanced Analysis II - N.D.Bình

Practice 6: Advanced Analysis II Practice 6: Advanced Analysis II ........................................................................................ 35 ArcView Steps ................................................................................................................ 35  Step 1 Network Analyst ............................................................................................. 35  Step 1.1 Find Best Route ........................................................................................ 36 Step 1.2 Find Closest Facility .................................................................................. 38 Step 1.3 Find Service Area ...................................................................................... 38 Step 2 3d Analyst ....................................................................................................... 39  Step 2.1 Interpolation to create a DTM ................................................................... 39 Step 2.2 Viewing a 3d image ................................................................................... 40 Step 2.3 Creating contours and obtaining area and volume ................................... 41 Step 2.4 Slope, aspect & hillshade .......................................................................... 42 Step 2.5 Viewshed ................................................................................................... 42 Step 2.6 Visualising your 3d image ......................................................................... 43 As you have seen from the lecture, both the network and 3d analyst extensions of ArcView are powerful tools. This practical will explore their functionality. Firstly, start ArcView, start a new project, add a view and set the working directory (to 'c:\temp'). ArcView Steps Step 1 Network Analyst As already mentioned the 'network analyst' is an extension, so we need to load the appropriate extension before we can proceed. Go to the 'File' menu and then 'Extensions', put a tick in the box corresponding to 'Network Analyst' and then click on 'OK'. Notice how a new menu 'Network' should now be visible, along with a new tool for adding point locations - which will currently be unavailable. We now require some sample data to experiment with. Add all of the themes from the directory 'c:\arcv32\arcviewlAv_gis32\avtutor\network\' customer.shp', 'del_Ioc.shp', 'hospital.shp', 's_fran.shp' and 'shorelin.shp'), You may wish to rearrange both the order of the themes and the symbols used as to make the themes more disguisable. A sample layout is illustrated below: Practice 6: Advanced Analysis II ERS 120: Principles of GIS N.D. Bình 36/59 If you go to the 'Network Analyst' menu you will see that all the options are presently unavailable - this is because it will only function if a line theme is active. Make the road theme ('S_franshp') active and go back into the 'network menu' –the functionality should now be available and we will now examine each option in turn. Step 1.1 Find Best Route This function will find the best way of getting from one point location to another, or the best way to visit several point locations. Within the 'S_fran.shp' attribute table you will see that the following fields are included: line length ('Metres'), the distance it is possible to drive within one minute ('Minutes') and the time taken to drive down the line segment (,Drivetime')' All of these fields can be used as distance estimates from one point to another (termed the cost field). 1. Make SUIe the line theme (' Sjranshp') is the only active theme 2. From the 'Network' menu choose 'Find Best Route' - this should bring up a problem definition dialog (as shown below) and add a new theme entitled 'Route1' to the 'Table of Contents'. 3. Click on the 'Properties' button within the problem definition dialog. From here we can choose the cost field, select 'Drivetime'. We can also select the working units (units that are used to report the total cost of the route) and number of decimal places. Select the options as shown below (remember to make these properties default) and then click 'OK': 4. We can now specify the start of the route, the locations or ' stops' to be visited along the way and the end of the route. There are two ways in which this can be done. Firstly, a point theme can be loaded in using the ' load stops' button within the problem definition dialog. However, we can also click on the map at the points we require by using the 'Add locator' tool . Select this tool and then click twice on the map on road segments at opposite ends of the map (as illustrated below). The graphical points placed on the map should appear in the dialog as illustrated by the following figure. Practice 6: Advanced Analysis II ERS 120: Principles of GIS N.D. Bình 37/59 If you specify an event that doesn't fall within a certain distance (1/100th the vertical or horizontal line extent - whichever is more), you will be prompted if you wish to add it anyway. If you select 'yes' the event will be marked as a red symbol in your view - but will not be used to solve a problem unless you move it with the pointer tool ( ) into a more acceptable location. 5. Now click on the 'Solve' button ( ) to calculate the optimum route. The time taken is reported within the dialog box. Directions are also attainable using the appropriate button. You can close the problem definition dialog. 6. We are now going to create the best route between the locations a transport firm needs to deliver to ('Del_Ioc.shp'). We no longer require the theme 'Routel' active or visible (note route themes are only temporary held, to properly save the route use the 'Convert to shapefile' option). Again go to the problem definition dialog for 'Find Best Route'. This time, to select the stops click on the 'load stops' button and select 'Del_loc.shp'. 7. It is possible to create the order that the stops will be visited by clicking on the label of the stop and using the 'up' and ' down' buttons ( & ). The stop at the top of the list will be visited first - briefly experiment with this. However, we wish to find the best route between the locations so check the 'Find best order' selection box. 8. Currently there is no depot for the driver - so using the 'Add locator' button place a depot location anywhere on the map. Next move the 'graphic pick l ' label up to the top of the list (representing the depot), as illustrated below. We also wish the driver to return to the depot after they have finished - so select the 'Return to origin' box. Now click on the 'Solve' button ( ) Practice 6: Advanced Analysis II ERS 120: Principles of GIS N.D. Bình 38/59 9. Explore the route and the time taken between each stop - does it look plausible? You can now close the dialog box and delete the route themes created (make them active and use 'Delete themes' option within the 'edit' menu). Step 1.2 Find Closest Facility Here the 'Network Analyst' identifies the closest facility (out of a number of points contained within a theme) and displays the best route there. First we may have to select the event location If the appropriate event theme has a small number of points (as is the case for 'Del_loc.shp' -15 records) this can be done within the problem definition dialog for 'Find Closest Facility'. However, if there are numerous records (for example 1,432 for "Customer.shp') it is best to select the possible events prior to starting. Enter the attribute table within "Customer.shp' and randomly select five records (not from the same street! I). Only these selected records will be used now when the theme is selected for analysis. 1. Make sure the only active theme is the 'Sjran.shp' theme and select 'Find Closest Facility' from the 'Network Analyst' menu. 2. From within the problem definition dialog select the point theme representing the 'facilities' from the drop down list - in this case 'Hospital.shp'. 3. Select the event theme - "Customer.shp' from 'Load Events'. We selected five customer locations, however, each will have to be selected and the analysis carried out in tum 4. Select how many facilities you wish to find - select just one to begin with 5. Solve the first problem 6. We can now select the next event from the list and solve this problem. Repeat the process for all five customer locations and experiment with finding varying numbers of facilities 7. Once finished, close the dialog box and delete the temporary theme (' fac l ") Step 1.3 Find Service Area The 'Network Analysis' provides two tools that allow you to learn what is near to a particular site: service networks and service areas. Service networks identify the accessible streets within a specific travel time or distance. Service areas identify the region that encompasses the accessible streets. 1. Make sure the only active theme is the 'S_fran.shp' theme and select 'Find Service Area' from the 'Network Analyst' menu 2. Click on 'Load sites' and select the 'Hospital.shp' theme 3. We can now select the cost field that will define the extent of the service area and network around the site (for example everywhere within a five minuets drive from the hospitals). To do this double click in the 'minutes' field and select your chosen drive time. 4. The option is also available (as for 'find closest facility') to 'travel from' or 'travel to' the site. Although this makes little difference unless one way systems are set up within your road attribute data 5. Service areas have the option of being compact - whereby they more accurately reflect the underlying road structure rather than the more general form used to speed calculation times 6. When finished, solve the problem and then close the dialog box. 7. We are now going to calculate the number of people residing within each catchment area. Make sure no records within the customer's table are selected ('clear selected features') and then select one ofthe service areas ('select feature' - as illustrated below). Next make 'Customer.shp' active and select the 'Select by theme' function within the 'Theme' menu. 8. Select a new set of features from the active theme that 'have their centre in' the selected features of the service area theme ('Sareal.shp'). Practice 6: Advanced Analysis II ERS 120: Principles of GIS N.D. Bình 39/59 9. We can now enter the customer theme attribute table to see how many records are selected. Repeat the process for the other three hospital service areas. Once finished you can close the view. Step 2 3d Analyst Load the 3d Analyst extension in the usual manner (=> file; => extensions) and then create a new view as illustrated by the cursor at the top of the figure to the right. A new menu should be visible entitle 'Surface', along with a new project type '3d scenes' - as illustrated in the figure to the right. We now require some sample data to experiment with. Add the following feature themes from the directory 'c:\arcv32\arcviewlAv_gis32\avtutor\3d\site2\': 'bldg.shp', 'mass_pt.shp' and 'roads.shp', as well as the image file - 'ortho.lan'. Examine the data source you have in your view. Step 2.1 Interpolation to create a DTM We are now going to make our own DTM (digital terrain model) from the spot height point data Practice 6: Advanced Analysis II ERS 120: Principles of GIS N.D. Bình 40/59 (tmassjn.shp'}. There are two ways in which this is possible - using a TIN or creating a grid; we will cover both in turn. Make the topology file (tmasspt.shp') active and then go to the 'Surface' menu and select 'Interpolate grid'. Select the grid extent to be the same as the image file (,ortho.lan') and to have 150 rows (remember that the cell size and number of columns will automatically be calculated if you press return after typing in the required number of rows). We can now select the interpolation method as either IDW or spline and various options for whatever best suits our application. We will use IDW with default settings - so just click 'OK'. A grid should have been produced similar to the one shown below: Now activate 'massjit.shp' and select 'Create TIN from features' from the 'Surface' menu. The height source refers to the field that contains the height field (in this case 'spot'). Verify that the 'input as' are point sources (mass points). Click on O.K. and suitably name your file. A TIN will now be created, how well do the TIN and grid compare? Step 2.2 Viewing a 3d image To view our DTM as a 3 dimensional image we must create a new '3d scene' from the project window (see step 2). We can add data to the 3d scene using the 'add theme' button ( ). Add the TIN you have just created. We now have to set the 3d scene properties - go to the '3d Theme' menu and select properties. Select the map units as metres and 'calculate' the vertical exaggeration. From here we can also change the sun azimuth and altitude - for now we will leave them as they are. Click on O.K., you should now see the surface as a 3d model. Experiment with the following tools within the viewer (especially the navigate tool): Practice 6: Advanced Analysis II ERS 120: Principles of GIS N.D. Bình 41/59 A TIN automatically creates a slope and aspect as well as elevation. Double click on the legend to access the legend editor and then change the legend from elevation to slope and then aspect (as shown over the page). We will now find out how to create slope and aspect for a grid theme as well as other functionality incorporated within the 3d analyst extension. Step 2.3 Creating contours and obtaining area and volume To create contours select the 'create contours' option from the 'surface' menu with the TIN active. Select to create contours every 10 meters, starting at a base height of O. Notice how the resulting theme appears to be below the actual DTM - this is because the TIN is using a 3d height source - whereas the contours in contrast are currently a flat 2d image. To correct this make sure the contour theme is active and then go to '3d Properties' within the 'Theme' menu. Assign the 'base height as' the surface for the TIN. Click on O.K. Note that most of Practice 6: Advanced Analysis II ERS 120: Principles of GIS N.D. Bình 42/59 the contours are still not visible - this is because they are located within the TIN, we really want them very slightly on top. Go back into the '3d Properties' menu and offset heights by 1. The contours are now over the top of the TIN - solving the problem. Using the 'Area and volume' function of the 3d analyst it is possible to calculate the area above or below a threshold elevation for a TIN source. Select this option and use it to create the area and mass of the DTM over 300 metres. Step 2.4 Slope, aspect & hillshade As already mentioned if we were using a grid instead of a TIN we would not have aspect or slope information and so these can be calculated by using the appropriate options from the 'Surface' menu. Create slope, aspect and hillshade for our TIN using the same grid extent as the TIN file and 150 rows. What applications can you think of for each of these possible functions? It is easy to convert from a grid to TIN and visa-versa using the 'convert grid to TIN' or 'convert to grid' options within the 'theme' menu. Step 2.5 Viewshed We will now create a viewshed - which represents the areas from which a particular feature can or can't be seen. First we have to create our point feature, this can't be done within the 3d scene and so close the scene by clicking on the close button within the legend - as illustrated to the right. Now open up 'viewz' again, create anew point theme (=> view; => new theme) with a suitable name. Place a single point (using draw point tool at the location shown below: - Practice 6: Advanced Analysis II ERS 120: Principles of GIS N.D. Bình 43/59 Save your edits (=> theme; => stop editing) and close 'view2' and return to your 3d scene and add the newly created point theme to the scene. Now make both the TIN and the point theme active before selecting 'Calculate viewshed' from within the 'Surface' menu. Create a grid with the same extent as the TIN and with 150 rows. A new Boolean theme will be created that shows where the feature point is visible from and where it is not. You may wish to assign the base height as the surface of the TIN to create the 3d view (=> theme; => 3d properties) as illustrated over the page. By converting your grid to a TIN it would be possible to calculate the area of land from where the feature is or not visible. Step 2.6 Visualising your 3d image In this final step we will combine a series of themes within a scene to create a final map of the area suitable for a report. Delete all the themes within the 3d theme except the original TIN. Now Practice 6: Advanced Analysis II ERS 120: Principles of GIS N.D. Bình 44/59 add the following themes from the directory 'c:\arcv32\arcviewlAv~s30 \avtutor\3d\site2\ '; 'bldg.shp' , and 'roads.shp' as well as the image file - 'ortho.lan' - remember these were the original themes you examined within section 2.0. Assign the base height of the all the themes (aerial photograph, buildings and roads) as the surface of the TIN. The roads will need to be offset by approximately 2 metres. The buildings contain height data within the attribute table, thus using the 'extrude features by height' option within the '3d properties' we can create the buildings as 3d shapes. Enter the 'height' field as the extruding feature - using the calculator tool ( ) and allow shading for features (as illustrated over the page). By editing the legend for the buildings it is possible to create a graded colour scheme based on the building height (select legend type as 'graded colour' and the classification field as 'height' – as shown over the page). You should now have you final image, which should be similar to that shown towards the bottom of the next page: - Experiment with some of the options you have been shown - including the vertical Practice 6: Advanced Analysis II ERS 120: Principles of GIS N.D. Bình 45/59 exaggeration factor and un azimuth and altitude ('3d scene' => 'properties') and the navigator tool for moving within the view (zoom in and have a closer look at your model). Once you have finished you can close ArcView, there is no need to save any files created during this practical. Last modified: Oct 25, 2009 ERS 120: Introduction to Geographic Information Systems /