Constructing Topographic Profiles with ArcGIS 10.x



Constructing Topographic Profiles with ArcGIS 10.xIntroductionTopographic profiles are used to provide a scaled “cut-away” slice view of a topographic surface along a specific azimuth. These are useful in a variety of scientific disciplines, but especially in Geology where the profile is the first step in the construction of a geologic cross-section. In a topographic profile the x axis represents the distance along the profile azimuth, and is always the same scale as the base map. Usually the ends of the profile are annotated with “A” to “A’” or something similar so that there is a cardinal direction sense to the profile. In general the profile should be constructed in the same map coordinate system as the base map from which it is derived, but offset below or to the side so that it does not interfere with the base map. In this example we will use a second data frame in the layout to contain the profile. FlowchartBelow is the generalized flowchart for creating the topographic profile in ArcGIS:center00Figure SEQ Figure \* ARABIC 1: Topographic profile flowchart.The following sections will present work-through examples of each of the above steps.Base Map SetupIn order to use the 3D Analyst tools you must add a 3D topographic data to your base map. In this project we will use the Talladega Springs, Alabama, 7.5’ topographic map available from the U.S. Geological Survey web site. A digital elevation model (DEM) and the digital raster graphic (DRG) of the topographic base map area can be downloaded simultaneously at the USGS National Map web site. The DEM raster contains the elevation information to the map, however, the 3D Analyst needs it in a TIN format so the initial step is to create a TIN from the DEM. Create a project file using UTM NAD27 zone 16 coordinate system and add the Talladega Springs DRG and DEM to the project file. Save it as “TopoProfile.mxd”. Expand the ArcToolbox and select the “3D Analyst Tools > Conversion > From Raster > Raster to TIN” option to activate the window dialog in Figure 2. Make sure that you direct the TIN output to your project folder for the Talladega Springs project. Select the “OK” button to generate the TIN. Name the TIN “tin_dem_m” because the elevations are in meters. After generating the 3D TIN model of the topography, you will need to define the line that represents the A to A’ cross section line. Use these coordinates to create a line feature class named “AAprime” with end-points:UTM_XUTM_YA :546641.43664873.4A’:558385.03651551.0Create this line feature in the Talladega Springs geodatabase file (TalladegaSprings.mdb). Create an “Annotation” feature class in “TalladegaSprings.mdb”, and add the labels “A” and “A’” to the end points of the cross section line. You should now have the elements depicted in Figure 3.Generate a 3D Cross-section Profile LineThe next step will intersect the 2D A-A’ cross-section line with the 3D TIN to create a 3D cross-section profile line containing numerous vertices that fall along the A-A’ line, but also have elevation values matching the TIN. To create this line use the toolbox “3D Analyst > Functional Surface > Interpolate Shape” selection. See the settings for the dialog window in Figure 4.This will generate a line (feature class = ”TopoProfile”) that has numerous vertices (everywhere a triangle in the TIN crosses the A-A’ line) that contain elevation values. Figure 5 contains a zoom in of the generated line in “edit vertex” mode. Note the elevation values attached to the vertices in the right edit sketch window. A 3D vertex is generated along the cross-section line wherever a TIN triangle boundary crosses the A-A’ line. Create a Profile GraphThe next step is to generate a graph of the distance of each vertex from the “A” origin of the cross-section, versus the elevation of the vertex in the 3D profile polyline. Do this using the 3D Analyst toolbar (activate now), and selecting in edit mode the 3D profile line. Now select the “Profile Graph or Point Graph” drop-down list, and then select “Profile Graph”. This will generate a graph object that will display a topographic profile of the 3D polyline along A-A’. “Right-click” on the graph object, and then select the “Export” option. Fill out the active dialog as in Figure 6 to create an Excel graph of the graph data. Figure 7 contains a screen capture of the Excel spreadsheet. Note that the 2nd column is the offset of the vertex from the “A” end of the cross-section line, and the 3rd column is the elevation of the vertex. The profile graph generated in the previous step plots the topographic profile, however, it will have random scales for the X direction so it will not be a true (VE=1) topographic profile. The data must be imported into a new project so that you can control the XY scaling to obtain a 1:1 profile.Create a New Topographic Profile ProjectSave work done in the Talladega Springs ArcMap project, then use the “File > New” to create a new ArcMap project that will contain the topographic A-A’ profile. Create a new project file named “Cross-Section” using UTM zone 16 NAD27 coordinate system (same as quadrangle project). Use the “Add Data XY data” button to add the coordinates in the Excel file created in the previous step (“TopoProfile.xls”). The profile should now appear as a series of closely spaced points. For the next step the imported profile points need to be converted into a true point feature class. Create a new geodatabase named “Cross-Section.mdb” in the project folder. Next right-click on the feature class name, and then select “Data > Export Data” to convert to a point feature class named “3Dpoints”. Send the new feature class to “Cross-Section.mdb”.Next turn the “3Dpoint” point geometry into a polyline with the toolbox selection “Data Management Tools > Features > Point to Line”. The dialog activated by this selection is displayed in Figure 8. Fill out the dialog as indicated in the figure. This will add a new polyline feature that smoothly connects through all of the profile points. The polyline is saved to the “Cross-Section” geodatabase feature class “Profile” (Figure 9). Add these additional feature classes to the “Cross-Section.mdb” geodatabase file:Feature ClassGeometryDescriptionGridlinetopographic profile gridAnnotationannotationtopographic profile textCompleting the Topographic Profile Cross-sectionCompleting the topographic profile will consist of adding the following elements and annotations:Bounding box around the profile.Grid lines and tic marks for elevation.Tic marks for distance on X axis.Annotation indicating the orientation of the cross-section.The above items can be added with drawing and editing commands that create/manipulate items in the “Grid” and “Annotation” feature classes. First, determine the length of the A to A’ cross-section line. This information is contained in the “profile.xlsx” file generated earlier because the x coordinate in that file is the distance offset from the “A” end of the line. The last row in the spreadsheet reads:IndexXY77617759.46189.65 Therefore, the length of the cross-section is 17,759.46 meters. You can now draw the base line of the cross section by constructing a line from coordinates (0,0) to (17759.46,0). Draw this in the “grid” feature class using “absolute” coordinates. At this time activate “Edit” mode and draw in the line using the above absolute coordinates. Remember that whenever you have an active “create feature” pointer you can right-click the mouse to select absolute coordinates. After drawing the baseline of the grid you need to make copies at 500 meter vertical intervals to cover the elevation range +2000 meters to -1000 meters. Select the baseline with the select tool – it should be highlighted if it is selected. Use “Edit > Copy” and then “Edit > Paste” menu selections to copy-and-paste a copy of the baseline on top of the original. The copy will remain highlighted. From the “Editor” drop-down list select “Move” and then fill in the “Delta X and Y” dialog box with 0 and 500 respectively for X and Y offsets. This will place the copy exactly 500 meters above the first. Continue the process until all elevation grid lines are produced. The ArcMap view should appear similar to Figure 10.Continue to build the cross-section by adding the left and right sides of the graph utilizing the “snap to endpoint” feature in the snapping toolbar. This allows you to precisely begin and end line segments at the endpoints of existing lines. See Figure 11. Continue to use the create feature and edit commands to complete the cross-section until it appears like Figure 12.Adding the Topographic Profile to an Existing Geologic Map LayoutArcMap projects may contain more than one data frame- a fact that we can use to good effect to display the newly constructed topographic profile in the Talladega Springs geologic map layout. With the geologic map loaded in ArcMap use the main menu “Insert > Data Frame” in data view mode. You will see the map window go blank and a new data frame name appear in the TOC window. Proceed to add the “grid”, “profile”, and “annotation” features from “cross-section.mdb”. Name the new data frame “Cross-Section A-A’”. Now switch to layout view and re-size the topographic profile data frame to fit within the layout limits. The layout window should appear similar to Figure 13. centercenter003092456969125Figure SEQ Figure \* ARABIC 2: Converting a DEM raster to TIN.Figure SEQ Figure \* ARABIC 2: Converting a DEM raster to TIN.-44455786120Figure 3: Layout of Topographic Profile with A-A' line added.Figure 3: Layout of Topographic Profile with A-A' line added.centercenter004572006993890Figure 4: Dialog window setup for "3D > Functional Surface > Interpolate Shape".Figure 4: Dialog window setup for "3D > Functional Surface > Interpolate Shape".centercenter00-31755786120Figure 5: 3D vertices generated by the "Interpolate Shape" 3D tool.Figure 5: 3D vertices generated by the "Interpolate Shape" 3D tool.centercenter04572005824220Figure 6: Export profile graph as Excel file window dialog settings.Figure 6: Export profile graph as Excel file window dialog settings.centercenter006858006686550Figure 7: Screen capture of profile graph data opened in Excel.Figure 7: Screen capture of profile graph data opened in Excel.centercenter004572006993890Figure 8: Dialog activated by toolbox "Data Management > Features > PointToLine".Figure 8: Dialog activated by toolbox "Data Management > Features > PointToLine".centercenter00-31755786120Figure 9: ArcMap zoomed view of topographic profile after the "PointToLine" tool.Figure 9: ArcMap zoomed view of topographic profile after the "PointToLine" tool.centercenter005840730Figure 10: ArcMap view after elevation grid lines are copied at 500m intervals.Figure 10: ArcMap view after elevation grid lines are copied at 500m intervals.centercenter005780405Figure 11: Using endpoint snap to square off the left side of the cross-section.Figure 11: Using endpoint snap to square off the left side of the cross-section.centercenter0-31755786120Figure 12: Completed ArcMap cross-section diagram.Figure 12: Completed ArcMap cross-section diagram.centercenter0-44455786120Figure 13: Cross-section added to Geologic Map layout in a separate data frame.Figure 13: Cross-section added to Geologic Map layout in a separate data frame.centercenter00 ................
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