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| <!DOCTYPE html> | ||
| <html lang="en"> | ||
| <head> | ||
| <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> | ||
| <title>GIS/MEA582: Geospatial Modeling and Analysis</title> | ||
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| <link rel="shortcut icon" href=".././img/favicon.ico" /> | ||
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| <link href="../layout.css" rel="stylesheet" type="text/css" media="screen"> | ||
| <link href="../style.css" rel="stylesheet" type="text/css" media="screen"> | ||
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| <body> | ||
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| <div id="outercontainer"> | ||
| <div id="container"> | ||
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| <header> | ||
| <div id="header-image"> | ||
| <h1>NCSU GIS/MEA582:<br>Geospatial Modeling and Analysis</h1> | ||
| </div> | ||
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| <nav> | ||
| <ul class="nav"> | ||
| <li><a href="../index.html">Syllabus</a></li> | ||
| <li><a href="../schedule.html">Schedule</a></li> | ||
| <li><a href="../topics/course_intro.html">Introduction</a></li> | ||
| <li><a href="../logistics.html">Logistics</a></li> | ||
| <li><a href="../topics/index.html">Topics</a></li> | ||
| <li><a href="../projects.html">Projects</a></li> | ||
| <li><a href="../faq.html">FAQs</a></li> | ||
| </ul> | ||
| </nav> | ||
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| </header> | ||
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| <main> | ||
| <!-- This is a generated file. Do not edit. --> | ||
| <h2>Buffers, cost surfaces, least cost path</h2> | ||
| <p>Resources: | ||
| <a href="https://www.lib.ncsu.edu/gis/virtcamp.html">ESRI virtual campus</a> | ||
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| <p> | ||
| Include resulting maps into your report | ||
| (use your judgment to decide which results to include). Adjust the colors and symbology of displayed layers to match the cartographic standards (lakes are displayed in blue etc.) | ||
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| <!-- <pre> | ||
| ======================================================================== | ||
| ALL COORDINATE SYSTEMS MUST BE DEFINED TO RUN BUFFER (i.e. .prj files) | ||
| ======================================================================== | ||
| </pre> --> | ||
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| <p> | ||
| Create the workspace for the current assignment as the folder Buffers_cost<br> | ||
| <p> | ||
| To constrain analyses in a similar manner as g.region, | ||
| set the spatial extent using the options under Environments, for example:<br> | ||
| to constrain analyses results to the extents defined by intersection of input features:<br> | ||
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| <pre> | ||
| Start ArcMap. | ||
| From the menu Geoprocessing -> Environments... -> Processing extent. | ||
| Choose Intersection of Inputs from the drop down menu. | ||
| Click 'OK' | ||
| </pre> | ||
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| <p> | ||
| <!-- You can create a bounding polygon of the "elev" DEM by using the 3D Analyst Tools. Check out 3D Analyst (if you haven't already) > Open ArcToolbox > 3D Analyst Tools > Conversion > From Raster > Raster Domain | ||
| Input = "elev" | ||
| Output = "name your file" | ||
| Output Type = Line or Poly (I tend to use Poly so I can calculate area) | ||
| Then when you are clipping the extent of the Data Frame you can use the extent of your new file, instead of copy/pasting or writing down the extent of the raster. --> | ||
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| To work on a subset, clip your data to a given spatial extent.<br> | ||
| Constrain the drawing of project layers to a user specified extent. | ||
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| <pre> | ||
| Start -> Programs -> ArcMap | ||
| Add ./ncrast.mdb/elev | ||
| Add ./ncshape.mdb/streets_wake | ||
| Dbl. Click the 'elev' layer in the TOC | ||
| Go to -> Layer Properties -> Extent | ||
| Write down the four numbers in the text fields labeled: 'Left', 'Right', 'Top', 'Bottom' | ||
| Click 'OK' | ||
| Dbl. Click 'Layers' in the TOC | ||
| Go to ->'Data Frame Properties' -> 'Data Frame' -> 'Clip Options' -> 'Clip to Shape' | ||
| Click 'Specify Shape' | ||
| Select 'Custom Extent' | ||
| Uncheck the 'Degrees' check box | ||
| Enter the four numbers you recorded earlier in their appropriate text fields | ||
| Click 'OK' | ||
| Click 'OK' | ||
| </pre> | ||
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| <h3>Find developed areas close to lakes</h3> | ||
| Create the buffers: | ||
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| <pre> | ||
| File -> Add Data -> Add Data... | ||
| Select ./ncrast.mdb/lakes | ||
| Select ./ncrast.mdb/landcl96 | ||
| Check out a Spatial Analyst Extension license (Menu -> Customize -> Extensions -> Spatial Analyst box needs to be checked) | ||
| Open the ArcToolbox (you may already have it open) | ||
| Select 'Spatial Analyst Tools->Distance->Euclidean Distance' | ||
| Set 'Input raster' to 'lakes' | ||
| Set Output distance raster' to '\Buffers_cost\lk_dist' | ||
| Set 'Maximum distance' to '500' | ||
| Leave the rest as defaults | ||
| Click 'OK' | ||
| </pre> | ||
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| <p> | ||
| Select the locations that overlay developed areas: | ||
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| <pre> | ||
| Select 'Spatial Analyst Tools->Map Algebra->Raster Calculator' | ||
| Type in the expression: SetNull( "landcl96" > 2, "lk_dist") | ||
| Set the Output raster to './Buffers_cost/dev_lakes | ||
| Click 'OK' | ||
| </pre> | ||
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| <h3>Compute cost surface from accident based on speed limits</h3> | ||
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| <pre> | ||
| File -> Add Data -> Add Data... | ||
| Select ncshape.mdb/streets_wake | ||
| Open the ArcToolbox (if not already open) | ||
| Select 'Conversion Tools->To Raster->Polyline to Raster' | ||
| Set 'Input Features' to 'streets_wake' | ||
| Set 'Value field' to 'SPEED' | ||
| Set 'Output Raster Dataset to './Buffers_cost/str_speed' | ||
| Set Cellsize to 30 | ||
| Leave the others as defaults | ||
| Click 'OK' | ||
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| File -> Add Data -> Add Data... | ||
| select ./ncshape.mdb/fire_pt | ||
| </pre> | ||
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| <p> | ||
| Set the working directory: | ||
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| <pre> | ||
| Select Geoprocessing -> Environments... | ||
| Under 'Workspace' set the 'Current Workspace' to '.\Buffers_cost' | ||
| Under 'Raster Analysis' set the 'Cell Size' to 'Same as layer str_speed' | ||
| Under 'Raster Analysis' set the 'Mask' to '.\ncshape.mdb\boundary_wake' | ||
| Click 'OK' | ||
| </pre> | ||
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| <p> | ||
| Assign travel time per cell in hours, compute cost surface.<br> | ||
| Assign null values a speed of 5. | ||
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| <pre> | ||
| Open the ArcToolbox (if not already open) | ||
| Select 'Spatial Analyst Tools->Map Algebra->Raster Calculator' | ||
| Type in the expression: Con(IsNull("str_speed"),5,"str_speed") | ||
| Set the Output raster to 'str_speed2' | ||
| Click 'OK' | ||
| </pre> | ||
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| <p> | ||
| Calculate the travel time and cost surface. | ||
| <p> | ||
| In ArcGIS cost is defined per <em>map unit</em> (meters in this case). | ||
| We create a cost raster where cost is time to cross one map unit. | ||
| <span class="question">Where does the 0.00062137 constant come from?</span> | ||
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| <pre> | ||
| Select 'Spatial Analyst Tools->Map Algebra->Raster Calculator' | ||
| Type in the expression: 0.00062137 / "str_speed2" | ||
| Set the 'Output raster' to str_trv | ||
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| Open the ArcToolbox (if not already open) | ||
| Select 'Spatial Analyst Tools->Distance->Cost Distance' | ||
| Set 'Input raster or feature source data' to 'fire_pt' | ||
| Set 'Input Cost raster' to 'str_trv' | ||
| Set 'Output distance raster' to './Buffers_cost/str_cost' | ||
| Set 'Output backlink raster (optional)' to './Buffers_cost/backlink' | ||
| Leave the rest as defaults | ||
| Click 'OK' | ||
| </pre> | ||
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| <h3>Find cost from selected firestations</h3> | ||
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| <pre> | ||
| File -> Add Data -> Add Data... | ||
| Select ./ncshape.mdb/firestations | ||
| Open the ArcToolbox (if not already open) | ||
| Select 'Spatial Analyst Tools->Extraction->Sample' | ||
| Set 'Input rasters' to 'str_cost' | ||
| Set 'Input Location raster or point features' to 'firestations' | ||
| Set 'Output table' to './Buffers_cost/station_costs' | ||
| Leave everything else as defaults | ||
| Click 'OK' | ||
| </pre> | ||
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| <p> | ||
| Add the table of costs (NOTE: in Arc 10 this should be added automatically at the bottom of the TOC). | ||
| However, if the table does not get added: | ||
| <pre> | ||
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| File -> Add Data -> | ||
| Select '.\Buffers_cost\station_costs' | ||
| </pre> | ||
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| <p> | ||
| Open the station_costs table and sort on the field 'STR_COST': | ||
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| <pre> | ||
| <i>right click</i> 'station_costs' -> Open | ||
| <i>right click</i> column named 'STR_COST' and choose 'Sort Ascending' | ||
| Note the range of cost values. | ||
| Close the table | ||
| </pre> | ||
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| <!--<p> | ||
| #create the cost backlink (direction grid) | ||
| Open the ArcToolbox (if not already open) | ||
| Select 'Spatial Analyst Tools->Distance->Cost Back Link' | ||
| Set 'Input raster or feature source data' to 'fire_pt' | ||
| Set the 'Input cost raster' to 'str_cost' | ||
| Set the 'Ouput Backlink raster' to '.\Buffers_cost\backlink' | ||
| Click 'OK' --> | ||
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| <p> | ||
| Find shortest path from nearby firestations.<br> | ||
| Note: create the firestations as a shapefile if the below | ||
| does not work with geodatabase firestations. | ||
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| <pre> | ||
| Open the ArcToolbox (if not already open) | ||
| Select 'Spatial Analyst Tools->Distance->Cost Path' | ||
| Set 'Input raster or feature destination data' to 'firestations' | ||
| Set 'Destination field' to 'OBJECTID' | ||
| Set the 'Input cost distance raster' to 'str_cost' | ||
| Set the 'Input cost backlink raster' to 'backlink' | ||
| Set the 'Output raster' to '.\Buffers_cost\cost_path' | ||
| Set the 'Path type' to 'BEST_SINGLE' | ||
| Click 'OK' | ||
| </pre> | ||
| <p> | ||
| Note: to see the resulting least cost (drive-time) path | ||
| you may have to turn off some or most of the layers in your TOC. | ||
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| </main> | ||
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| <footer> | ||
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| <nav> | ||
| <ul> | ||
| <li><a class="term-changes" href="https://moodle-courses2425.wolfware.ncsu.edu/course/view.php?id=1183">Moodle site</a></li> | ||
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| <li> | ||
| <a href="https://github.com/ncsu-geoforall-lab/geospatial-modeling-course" title="Source code for web pages on GitHub"> | ||
| <img src="../img/github_logo.png" alt="GitHub Octocat logo"> | ||
| </a> | ||
| </li> | ||
| <li title="Copyright and license (not applicable to linked materials)"> | ||
| © 2008-2024 | ||
| <a href="https://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a> | ||
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| </ul> | ||
| </nav> | ||
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