MD iMAP | LiDAR FAQ

LiDAR FAQ

What is LiDAR?

 
LiDAR, which stands for Light Detection And Ranging, is a remote sensing method that uses light in the form of a pulsed laser to measure ranges (variable distances) to the Earth. These light pulses combined with timing and locational data recorded by the laser system generate precise, three-dimensional information about the topography, vegetation and other features on the earth’s surface.

Source: What is LiDAR? NOAA, January 22, 2013
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How is LiDAR Used?

 
Elevation data are essential to a broad range of applications, including forest resources management, wildlife and habitat management, national security, recreation, and many others. For the State of Maryland, elevation data are critical for agriculture and precision farming, natural resources conservation such as the Chesapeake Bay and its watershed, flood risk management, urban and regional planning, infrastructure and construction management, water supply and quality, coastal zone management, and other business uses. Today, high-density light detection and ranging (LiDAR) data are the primary sources for deriving elevation models, LiDAR point data and other associated datasets.

Carswell, William J., Jr. The 3D Elevation Program—Summary for Maryland Report.​
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What LiDAR Services Are Available?

 
The Maryland LIDAR server has been created to provide open access to elevation information for use in a variety of studies and applications. The Maryland LIDAR server maintains the best available elevation data and provides image services in both county and statewide extents.

The Maryland LiDAR server supports multiple image services per county and statewide:
  • Aspect
    • Aspect identifies slope direction, in compass degrees, where 0 = north and 180 = south. Aspect determines how much sunlight will strike the earth’s surface, which has impacts on ecology, vegetative habitats, soil moisture and many other landscape characteristics.
  • Shaded Relief
    • Shaded relief visualizations offers a more dynamic and traditional view of the digital elevation models (DEMs). There are many ways to produce a shaded relief. A more recent application, used for these products, applies a color ramp to the elevation values.
  • Digital Elevation Model (DEM) in Feet and Meters
    • A DEM is a raster representation of the earth’s surface created from LiDAR elevation data. DEMs are utilized for a variety of purposes including hydrology modeling and viewshed analysis.
  • Hillshade
    • Hillshade is used to determine the illumination of the earth’s surface. It can be used in analysis to understand the time and intensity of the sun at a given location or for graphical display purposes to enhance the relief of a surface, such as for a shaded relief.
  • Slope
    • Slope identifies the inclination of the earth’s surface. The degree or percent of a slope is an important factor when analyzing slope stability, transportation, agriculture, recreation, etc. Slope can be used alone or in conjunction with other layers for various site suitability analysis.

What if I Need to Examine a Large Area?

 
County mosaics are avail​able in Esri GRID format and are ideal when performing analysis on large areas. Visit the LiDAR Download Pre-Defined DEMs page​ for links to the most current year which include metadata, .ovr pyramids and bare earth DEMs. Please contact the Eastern Shore Regional GIS Cooperative (ESRGC) at esrgc@salisbury.edu for inquiries regarding the available DEMs.​​​​​​​​​​​

How Do I Access LiDAR Services from ArcGIS Desktop?

 
Follow the instructions listed below:
  1. Launch ArcMap
  2. Navigate to the ArcCatalog tab
  3. In the ArcCatalog window expand GIS Servers
  4. Select Add ArcGIS Server
  5. Select Use GIS Services and Click Next
  6. Enter the Server URL: http://lidar.geodata.md.gov/imap
  7. Click Finish (An pop-up may notify that the connection was successfully made.)
  8. The new server connection will appear in the ArcCatalog window. After expanding the server, select the desired image service.
Note: Overviews were created for each of the services to enable faster display of the image data. Overviews provide lower resolution representations of the data which affect the values that are reported at certain zoom levels using the identify tool. Overviews do not affect the exporting/clipping of data however when identifying elevation values, be sure to zoom to raster resolution to ensure the correct vales are reported.
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How Do I Apply Raster Function Templates?

 
Follow the instructions listed below:
  1. Launch ArcMap
  2. Add in the countywide dem_m service
  3. Right click the service in the Table of Contents, Select Properties
  4. In the Layer Properties window, Select Server Functions tab
  5. Select the Functions drop-down
  6. Choose one from the following function: Aspect, DEM_FT, Hillshade, None, Slope, Stretched
  7. Click Apply
  8. Click OK
  9. Select Symbology, Scroll down to Statistics, Select From Current Display
  10. Click Apply
  11. Click OK
Note: ArcGIS Desktop enables the use of raster functions. Functions provide users with fast on-the-fly processing options without changing the actual data. Raster functions have been added to all of the countywide dem_m image services.​​​​
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How Do I Access LiDAR Services from ArcGIS Online (AGOL)?

 
To view LiDAR services in AGOL, click any of the buttons on the County Services or Statewide Services pages or search for LiDAR from the ArcGIS Online for Maryland Gallery.

How Do I Access LiDAR Services from Google Earth?

 
Follow the instructions listed below:
  1. Select the image service URL to open the service REST page
  2. On the REST page, Select View In: Google Earth. This will prompt the download of a .kmz file
  3. Open Google Earth and Select File > Open
  4. Navigate to the download directory, Select the downloaded service and Select open
  5. Double click the service once it appears under the "Places" tab to zoom to the service extent
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How Do I Access LiDAR Services from AutoCAD?

 
Follow the instructions listed below:
  1. Start AutoCAD
  2. Click the Add Image Server Connection on the Image Server toolbar
  3. In the Add Image Server Connection window, type the name of the LiDAR server: http://lidar.geodata.md.gov/imap in the Server Name text box
  4. Double click the Elevation folder to view the contained services
  5. Double click the image service in the list or Click on the iamge service and Click Select to to add the image service to the Selected Services list
  6. The Service Properties window is displayed. This window shows the image service metadata and properties that you can view before opening the image service.
  7. Click OK to close the Add Image Server Connection window
Instructions provided by Esri Resources
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How Do I Access LiDAR Services from MicroStation?

 
Follow the instructions listed below:
  1. Start MicroStation
  2. Click the Add Server Connection button in the MicroStation Image Server Client window
  3. In the Add Image Server Connection window, type the name of the LiDAR server: http://lidar.geodata.md.gov/imap in the Server Name text box
  4. Double click the Elevation folder to view the contained services
  5. Double click the image service in the list or Click the image service and Click Select to add the image service to the Selected Services list
  6. The Service Properties window is displayed. This window shows the image service metadata and properties that you can view before opening the image service
  7. Click OK to close the Add Image Server window
Instructions provided by Esri Resources
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How Do I Access LiDAR Services from QGIS?

 
Follow the instructions listed below:
  1. Launch QGIS
  2. Select Layer, Select Add WMS Layer, Select New
  3. Name the connection
  4. Navigate to the service WMS page from the REST services directory and copy/paste the link into the URL field (Note: These services do not require a username and password
  5. Select OK
  6. Select the service in the list of layers, Select Add, Select Close
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How Do I Extract Data for Use in Desktop Processing?

 
There are several methods to extract LiDAR data for use in desktop processing.

To extract based on a feature defined boundary
  1. Load the service and feature mask into ArcMap
  2. In ArcToolbox, Select the Extract by Mask tool under Spatial Analyst toolbox
  3. Select the image service as the input raster and the boundary feature class as the feature mask
  4. Specify the output raster name and directory location where the image will be saved and Click OK
  5. The image will be added to the map after processing
If you do not have the Spatial Analyst extension, use the Export by Data Frame Extent option.
  1. Load the service into ArcMap
  2. Zoom to the area of interest
  3. Right click the service in the Table of Contents and Select Data > Export
  4. From the Export window specify preferences and Click Save
  5. The image will be added to the map after processing
Note: The statewide services are a composite of the best available data from each county. If the area of interest is completely contained within a single county, we recommend using the countywide service to extract data. If the area of interest across two or more counties, the statewide service can be used, however users are advised to refer to the metadata documents to determine the appropriate cell size for the output raster.

Where Can I Find Metadata for the LiDAR Services?

 
Complete metadata is available for each county. Review the LiDAR Metadata Summary Table and click on each link for full metadata.

Metadata is also attached to each image service and can be viewed in ArcMap and ArcCatalog.​

Considerations for LiDAR Service Usage

 
These LiDAR data services are high-resolution and thus, extremely large. They are most appropriate for background display, location queries for spot elevations and extraction of small areas (less than 25 square miles). The ability to utilize the services will depend on both the internet download speed and the number of concurrent users on the hosting servers. If extracting data, please expect the process to take longer than you may be used to.

Please see the “How Do I Extract Data for Use in Desktop Processing” FAQ for more information on extracting data.

Additional LiDAR Resources

 
Maryland Department of Natural Resources - http://dnrweb.dnr.state.md.us/gis/data/
NOAA Digital Coast, United States Interagency Elevation Inventory - http://coast.noaa.gov/inventory
USGS National Map Viewer - http://viewer.nationalmap.gov/viewer
USGS Earth Explorer - http://earthexplorer.usgs.gov
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