nd/gis crea text lidar: files dem · page 2 lidar crea ng a dem crea ng a dem from a lidar text...
TRANSCRIPT
Lidar (Light Detec on And Ranging) is
a type of remote sensing. It works like
radar, except it uses light or laser beams
instead of radio waves.
www.library.carleton.ca/find/gis
Page 1
LiDAR:LiDAR: Crea ng a DEM Crea ng a DEM from Text Filesfrom Text Files
This Help Guide will show you how to:
ArcMap
Create a DEM from a Lidar text file
Global Mapper
Create a DEM from a Lidar (las) file in Global Mapper
*Note: Lidar Intensity (x, y, z, i) is also recorded with most lidar data. It records the reflec vity of a surface.
This data can be used to create a geo‐referenced image of the landscape. Lidar intensity can be rela ve to its
surroundings, and it is easily influenced by current condi ons. It should be researched well before use.
*Note: Lidar points are commonly grouped into by 1st returns
and 2nd returns. The 1 returned are also known as the
“Non‐Ground” points since they returned to the sensor first,
meaning they probably reflected off trees or buildings.
Conversely, the 2nd returns are some mes called the “Ground
Returns” since these points took longer to return to the sensor ,
and probably reflected off of the ground.
h p://www.vliz.be/v/images/thumb/2/29/Lidar_fig_03.jpg/250px‐Lidar_fig_03.jpg
Figure 1: A DEM created from one le of the Ga neau Park Lidar
data set.
The me it takes for the laser to travel from
the sensor (o en mounted on a plane or
helicopter) to the surface and back is used to
calculate the distance to an object.
Lidar can be used to provide highly accurate
eleva on data. The data is collected as points
with X, Y, Z values. These points can be also be
used to create DEMs.
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LiDAR
Crea ng a DEM Crea ng a DEM from a Lidar Text File in ArcMap
Crea ng a DEM from Lidar data in text file format (.txt) involves 4 steps:
Adding the .txt file into ArcMap
Display the XY Data as an Events layer
Export the Events Layer to a shapefile
Interpolate a raster surface (DEM) from these points
This demo is using the NCC 2009 Lidar ground points located at:
J:\_O awa_Ga neau_Region\Na onal_Capital_Commission\LiDAR\Ga neau_Park_2009\TXT\1_Ground_txt
Adding the .txt file(s) into ArcMap
Using the Add Data bu on , select
all the .txt sheets you are interested in,
then click Add. This will add the .txt file(s)
to the Table of Contents in AcrMap.
Displaying the Points
In the Table of Contents, right click on the .txt file you just
added. Select Display XY Data… to open the Display XY Data
window.
Fill out the parameters as shown in the Figure to the right.
Be sure to set the coordinate system!
The press OK.
This will draw a Events layer of points. (This might take a while
depending on how many files you added.)
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*Note: Each method uses different algorithms and it should be
researched to determine which is best for your dataset.
Expor ng the Event Layer to a Point Shapefile
In the Table of Contents, right click on the Events file you just created. Select Data> Export
Data… to open the Display Export Data window. In this window, click on the folder icon to
give the shapefile an output name and loca on. Press OK when you are done.
(It is generally a good idea to keep the sheet index number in the name.)
Crea ng a DEM from Lidar Data in Text File Format cont.
Interpola ng to Create a DEM
The last step in crea ng a DEM is to preform
an interpola on. In the Spa al Analysis
Toolbox, under Interpola ons, choose an
interpola on method.
Required Parameters:
Input Features: the Lidar point shapefile
Z value field: the Z field of the shapefile
Output raster: output name and loca on
Cell Size: select an appropriate cell size
The resul ng DEM can be seen at the top of
Page 1.
Once the export is completed, you can remove the Events layer and the original .txt file from the Table of Contents.
LiDAR
Crea ng a DEM
Page 4
Crea ng a DEM from LAS Files in Global Mapper
This demo is using the Ville De Ga neau 2007 Lidar located at:
J:\_O awa_Ga neau_Region\Ville_de_Ga neau\Lidar_2007\LAS\LAS_Full
Global Mapper has the advantage that it can quickly create a surface from LAS files without
having to use complex tools like ArcMap does.
Load the LAS files into Global Mapper
Click and drag the LAS files from a folder in
Window Explorer into Global Mapper.
2. An Unknown Projec on window will appear claim‐
ing there is no projec on associated with the LAS
file. Click OK to con nue to the Select Projec on
window.
3. Select the appropriate projec on and datum. Then
click OK
4. Next, the Lidar Load Op ons window will appear.
Under Load Type, make sure to select
Create Eleva on Grid.
5. The LAS file will open as a DEM in Global Mapper.
LiDAR
Crea ng a DEM
LoadLiDAR
Crea ng a DEM
The LAS file as a DEM in Global Mapper. This shows
a sec on of Ga neau Park.