floodplain modeling with lidar-derived terrain
DESCRIPTION
Floodplain Modeling with LiDAR-Derived TerrainTRANSCRIPT
Floodplain Modeling and Floodplain Modeling and Delineation with LiDAR-Derived Delineation with LiDAR-Derived
TerrainTerrain
Wisconsin Dept. of Natural ResourcesWisconsin Dept. of Natural Resources
Bureau of Watershed ManagementBureau of Watershed Management
FEMA Risk MAP ProgramFEMA Risk MAP Program
Katie McMahan – GIS Data ManagerKatie McMahan – GIS Data [email protected]@wi.gov
Chris Olds – Floodplain EngineerChris Olds – Floodplain [email protected]@wi.gov
Presentation OverviewPresentation Overview
LiDAR LiDAR
– ProductsProducts
TerrainTerrain
– Required feature classes (surface feature types)Required feature classes (surface feature types)
– Process of buildingProcess of building
– Possible issues that may arisePossible issues that may arise
Floodplain delineationFloodplain delineation
– HEC-GeoRAS geometry to create input feature classesHEC-GeoRAS geometry to create input feature classes
– HEC-RAS to determine flood elevationsHEC-RAS to determine flood elevations
– HEC-GeoRAS mapping to delineate raw floodplain polygonsHEC-GeoRAS mapping to delineate raw floodplain polygons
– Smoothing and merging multiple floodplainsSmoothing and merging multiple floodplains
Products received Products received vs. vs.
what we usewhat we use Bare earthBare earth
• DEMDEM• DWGDWG• LASLAS• SHPSHP
BreaklinesBreaklines• DWGDWG• SHPSHP
ContoursContours• DWGDWG• SHPSHP
Point cloudPoint cloud• DWGDWG• SHPSHP• LASLAS
MetadataMetadata• Important elements:Important elements:
– ProjectionProjection– Average point Average point
spacingspacing
Terrain OverviewTerrain Overview
TIN-based dataset that is a representation of TIN-based dataset that is a representation of
input feature classesinput feature classes
Terrain is editable—can remove, add and Terrain is editable—can remove, add and
replace the data referencedreplace the data referenced
Steps to building terrainSteps to building terrain
Create a File Geodatabase
The personal geodatabase has a 2GB size limit, too small to handle an entire County’s worth of LIDAR data.
Feature DatasetFeature Dataset In ArcCatalog, create a new In ArcCatalog, create a new
‘Feature Dataset’. This will ‘Feature Dataset’. This will
house all data used to and house all data used to and
create your terrain. create your terrain.
Choose the coordinate system Choose the coordinate system
the LiDAR data is in; most the LiDAR data is in; most
often a County coordinate often a County coordinate
system.system.
Make sure the linear unit of Make sure the linear unit of
measurement (ft or meter) is measurement (ft or meter) is
defined correctly for both the defined correctly for both the
projected and vertical projected and vertical
coordinate systemscoordinate systems
Feature DatasetFeature Dataset
Import all of the features that will be used to create the Import all of the features that will be used to create the
terrain into feature dataset. terrain into feature dataset.
– LIDAR multipoints (created from LAS files)LIDAR multipoints (created from LAS files)
– BreaklinesBreaklines
– Hard-clip polygons (usually a buffered polygon of the Hard-clip polygons (usually a buffered polygon of the
County boundary) County boundary)
Determine Average Point Spacing of bare earth pointsDetermine Average Point Spacing of bare earth points
Average Point SpacingAverage Point Spacing
From LiDAR metadata or using the 3D Analyst Point From LiDAR metadata or using the 3D Analyst Point File Information toolFile Information tool
Average Point SpacingAverage Point Spacing
Bare Earth MultipointsBare Earth Multipoints
Multipoints should be Multipoints should be
spatially clusteredspatially clustered
Processing terrain Processing terrain
countywide: break countywide: break
down by township or down by township or
rangerange
Recent example: Recent example:
– 830 LAS files830 LAS files
– LiDAR points: LiDAR points:
2,074,016,0002,074,016,000
LAS to MultipointLAS to Multipoint
LAS to MultipointLAS to Multipoint
BreaklinesBreaklines Lines with height recorded at each vertex Lines with height recorded at each vertex
Represents some sort of interruption in the landscape:Represents some sort of interruption in the landscape:
– Natural landforms (ridges, valleys) - SNatural landforms (ridges, valleys) - S
– Edge of pavement - HEdge of pavement - H
– Roadways - HRoadways - H
– **Water lines (streams, rivers, canals, shorelines) - H**Water lines (streams, rivers, canals, shorelines) - H
Eliminates interpolation of LiDAR points across the breakline; becomes the edge of the Eliminates interpolation of LiDAR points across the breakline; becomes the edge of the
trianglestriangles
Hard lineHard line: represents distinct break in the slope: represents distinct break in the slope
Soft lineSoft line: allows the adding of edges without affecting the shape of the surface: allows the adding of edges without affecting the shape of the surface
**Taken from ArcGIS **Taken from ArcGIS Desktop Help 9.3.1Desktop Help 9.3.1
Hard Hard BreaklinesBreaklines
Clip PolygonClip Polygon Define boundaries for interpolating a terrain surface with an Define boundaries for interpolating a terrain surface with an
irregular shape—data that falls outside the polygon is excludedirregular shape—data that falls outside the polygon is excluded
Study area boundary Study area boundary
No height sourceNo height source
**Taken from ArcGIS **Taken from ArcGIS Desktop Help 9.3.1Desktop Help 9.3.1
Build Build TerrainTerrain
Choose FeaturesChoose Features
Pyramid TypePyramid Type
Terrain PyramidsTerrain Pyramids Levels of detail to improve efficiency—a form of scale dependent generalization Levels of detail to improve efficiency—a form of scale dependent generalization
(thinning points)(thinning points)
Z-ToleranceZ-Tolerance: uses a vertical tolerance in the definition of the terrain resolution at : uses a vertical tolerance in the definition of the terrain resolution at
the specified scale (relative to vertical accuracy at full-resolution)the specified scale (relative to vertical accuracy at full-resolution)
– Used to improve analysis performance through a range of scalesUsed to improve analysis performance through a range of scales
Window SizeWindow Size: resolution defined by window : resolution defined by window
– Used for improving interactive display performance (specific vertical Used for improving interactive display performance (specific vertical
accuracies is not a primary concern)accuracies is not a primary concern)
When exporting rasters or TINs, the entire feature dataset is used (no difference When exporting rasters or TINs, the entire feature dataset is used (no difference
from actual surface).from actual surface).
**Not necessary for terrain use at constant and large display scale, i.e. raster **Not necessary for terrain use at constant and large display scale, i.e. raster
production for large-scale applications or for data storage purposes; time production for large-scale applications or for data storage purposes; time
intensive, no reason to incur the processing cost.intensive, no reason to incur the processing cost.
Z-Tolerance Z-Tolerance
Must generate Must generate one pyramid no one pyramid no matter which matter which type you choosetype you choose
Summary of terrain settingsSummary of terrain settings
Terrain OverviewTerrain Overview
Coarsest representation of the terrain datasetCoarsest representation of the terrain dataset
For fast drawing at small scalesFor fast drawing at small scales
Set only those feature classes that must be Set only those feature classes that must be
represented in the overview to ‘Yes’represented in the overview to ‘Yes’
Terrain OverviewTerrain Overview
**Taken from ArcGIS Desktop Help 9.3.1**Taken from ArcGIS Desktop Help 9.3.1
3D Analyst Conversion Tool: 3D Analyst Conversion Tool: Terrain to RasterTerrain to Raster
Float will allow the value of the pixel to be in decimal format
5-foot cell size
Conversion to rasterConversion to raster
Countywide 5-foot gridCountywide 5-foot grid
3D Analyst license is required; 3D Analyst license is required;
Choose LAS over ASCII (if available); Choose LAS over ASCII (if available);
The data involved should be contiguous;The data involved should be contiguous;
Data should be in a projected coordinate system;Data should be in a projected coordinate system;
More straightforward to have the z-values in same unit of measure as the x,y More straightforward to have the z-values in same unit of measure as the x,y
values; values;
Use data gathered using the same data collection specifications and accuracy Use data gathered using the same data collection specifications and accuracy
requirements. requirements.
Use the fewest feature classes possible; no large single point feature classes. Use the fewest feature classes possible; no large single point feature classes.
Use a multipoint feature class for large point collections (e.g., anything over Use a multipoint feature class for large point collections (e.g., anything over
500,000).500,000). Allow plenty of time for processing large areas of terrainAllow plenty of time for processing large areas of terrain
Tips for building terrainTips for building terrain
ComplicationsComplications
Missing tiles = visual confirmation of the terrain Missing tiles = visual confirmation of the terrain
– requires cooperation with original vendor to gather requires cooperation with original vendor to gather
complete datasetcomplete dataset
Incorrect height values = visual confirmation of the terrain (i.e. Incorrect height values = visual confirmation of the terrain (i.e.
giant spikes or dips in elevation) or in floodplain delineation giant spikes or dips in elevation) or in floodplain delineation
‘gaps’‘gaps’
– may result in the need for additional ground truthing or may result in the need for additional ground truthing or
survey cross sections along the streamsurvey cross sections along the stream
Floodplain delineation ‘gaps’Floodplain delineation ‘gaps’
Floodplain DelineationFloodplain Delineation
HEC-GeoRASHEC-GeoRAS
Creating Feature ClassesCreating Feature Classes
Creating Feature ClassesCreating Feature Classes
Populating Feature ClassesPopulating Feature Classes
Layer SetupLayer Setup
Layer SetupLayer Setup
Extracting Topological DataExtracting Topological Data
HEC-RASHEC-RAS
Importing GIS data into HEC-RASImporting GIS data into HEC-RAS
Cross section in HEC-RASCross section in HEC-RAS
Cross Section 3D ViewCross Section 3D View
Cross section results in HEC-RASCross section results in HEC-RAS
Flood profile in HEC-RASFlood profile in HEC-RAS
Exporting HEC-RAS results Exporting HEC-RAS results into GIS filesinto GIS files
Floodplain delineation using Floodplain delineation using HEC-GeoRASHEC-GeoRAS
Floodplain Delineation Floodplain Delineation Layer SetupLayer Setup
Importing HEC-RAS dataImporting HEC-RAS data
Importing HEC-RAS dataImporting HEC-RAS data
HEC-RAS data back in GISHEC-RAS data back in GIS
Flood Inundation MappingFlood Inundation Mapping
Water surface TIN generationWater surface TIN generation
Flood Inundation MappingFlood Inundation Mapping
Flood Inundation MappingFlood Inundation Mapping
Flood depth gridFlood depth grid
Floodplain boundary polygonFloodplain boundary polygon
Floodplain boundary polygon smoothingFloodplain boundary polygon smoothing
Floodplain boundary polygon smoothingFloodplain boundary polygon smoothing
Merging floodplain feature classesMerging floodplain feature classes
QUESTIONS?QUESTIONS?