Lidar Support: Difference between revisions

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The term [http://en.wikipedia.org/wiki/Lidar|LIDAR] refers to a technology known as LIght Detection And Ranging.  This technology is used to gather a large amount of survey data from fixed wing aircraft or helicopters as they fly over the survey region.  The technique has the ability to penetrate clear water up to a limited depth (maybe up to 20 meters but varies based on conditions).
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{{GMS Deprecated Feature}}
{{SMS Deprecated Feature}}
{{WMS Deprecated Feature}}
The term [http://en.wikipedia.org/wiki/Lidar| LIDAR] refers to a technology known as LIght Detection And Ranging.  This technology is used to gather a large amount of survey data from fixed wing aircraft or helicopters as they fly over the survey region.  The technique has the ability to penetrate clear water up to a limited depth (maybe up to 20 meters but varies based on conditions).


A LIDAR file (normally it has an extension of “.las”) is a survey file that includes data points gathered from a LIDAR system and processed.   
A LIDAR file (normally it has an extension of ".las" or ".laz") is a survey file that includes data points gathered from a LIDAR system and processed.   


== Importing a LIDAR File==
== Importing a LIDAR File==
When a lidar is read in, SMS uses the Global Mapper library.  A dialog appears to allow the user to specify importing options. Principally, the user specifies whether the data should be loaded as a raster or scatter.  Then create a [http://xmswiki.com/xms/Raster_Options|raster] or [http://xmswiki.com/xms/SMS:Scatter_Module|scatter set].  This dialog a
[[File:Lidar load Options.png|thumb|500 px|The ''LIDAR Load Options'' dialog]]
When a lidar is read in, the ''Lidar Load Options'' dialog appears to allow the user to specify importing options. Principally, the user specifies whether the data should be loaded as a raster or scatter.  Then create a [[Raster_Options|raster]] or [[SMS:Scatter_Module|scatter set]].  The options in the dialog are described as a point cloud (scatter set) or a grid (raster).


This dialog also lists all the data sources/types of data included in the file and allows the user to select which data types should be imported.


Global Mapper recognizes that it is a lidar file and asks if we want to read the data as a point cloud (scatter set) or a grid (raster) and lets us choose the point classifications and return types to read.
===Reading as a point cloud (scatter set)===


Reading as a point cloud (scatter set):
If the user selects point cloud, SMS creates both a scatter set and an image.  Note that because this is not a uniformly arranged set of data and thus not a raster, all of the raster editing options will be unavailable for this data. There are several options for the appearance of the image.  These include:
*Use Colors if Present (Elevations Otherwise) – The points in the LIDAR set are given a color.  This appears like a contour plot image.
*Color Elevations Using Current Shader – currently SMS does not allow the user to select shader options, so this option also appears as a contour plot image.
*Color by intensity – this results in a gray scale image.
*Color by classification – the points in the LIDAR set are colored based on their type.  This can be useful to see what types of data (layers) exist in the file.  If all the points in a file are the same type, the image is a single color.
*Color by random number – colored points – no documentation is available for this feature


If the user selects point cloud, GM returns a list of points as well as an image.  SMS adds the list of points as a scatter set and the image as an image.  There are several options for the image created by GM.  These include:
The scatter points created when reading a LIDAR file are not triangulated.  They must be triangulated to extract observation profiles or use them as source of bathymetry.
-Use Colors if Present (Elevations Otherwise) - contour plot image
-Color Elevations Using Current Shader (I don’t know how to change the shader from inside of SMS)
    - for my test case, this looks like the contour plot image.
- I suspect we could get a hillshade or other options if we exposed the GM
-Color by intensity
    - this is a gray scale - looks kind of crappy
-Color by classification
    - colored points - not too interesting if all points are of the same type
-Color by random number
    - colored points - I don’t know what these mean


Notes:
===Reading as an elevation grid (raster)===
    The scatter points are not triangulated.  They must be triangulated to extract observation profiles or use them as source of bathymetry.
    GM supports an option to convert the image to a raster.  Trent implemented this to not allow access to this option.  If we try to “Convert to Raster” then SMS will bring up the same GM dialog used to import in the first place, but only the Grid/Raster option does anything.  Also, in that case it does not seem to be the same raster that is generated when you read the file as a grid in the first place.


Reading as an elevation grid (raster):
If the user selects grid, XMS creates a raster and an image.  XMS adds the raster as a VTK raster and the image as an image.  The image appears as a hillshade.


If the user selects grid, GM returns a raster and an image.  SMS adds the raster as a VTK raster and the image as an image.  The raster image looks like a hillshade.  This option is much slower than the point cloud option.
This option is much slower than the point cloud option.


Options include:
Options include:
- Grid creation Options - Tight to Loose
* ''Elevation Grid creation Options'' – Tight to Loose
    - Loose (default) - for test case it created 63752617 points/cells
** Loose (default) – for a test case it created 63752617 points/cells
    - Medium - for test case it created 63714287 points/cells with some holes
** Medium – for test case it created 63714287 points/cells with some holes
    - Tight - for test case it created 15058938 points that are mostly disjoint
** Tight – for test case it created 15058938 points that are mostly disjoint
- If the lidar data is not a box, you can fill either the entire box or just the convex hull with gridded data.
* If the LIDAR data is not a box, SMS can fill either the entire box or just the convex hull with gridded data.


Holes left in the grid are also reflected as holes in the image.  The tighter the option, the slower the process appears to be.
Holes left in the grid are also reflected as holes in the image.  The tighter the option, the slower the process appears to be.


Notes:
==LIDAR Images==
    The image created by the read as a grid can not be converted to a raster (it already was).  It can also not be converted to a point cloud.  For this reason, Trent disabled the “convert to raster” option that is normally associated with an image.
Reading a LIDAR file always results in an [[SMS:Image|image]] in XMS.  For some images, XMS allows the conversion to a RASTER.  Since that option is available when reading the LIDAR file, this capability is not available for images created as a side effect of reading a LIDAR file.


General Options:
==General Options==
  In addition to filtering out point classifications, you can use the following options:
In addition to filtering out point classifications, XMS supports the following options:
- Preview mode - load 1 in N points (user specifies N)
* ''Use Previous Mode Load Only 1 in Every N Samples'' (user specifies N)
- Delete samples over N standard deviations from the mean (user specifies N)
* ''Delete Samples Over N Standard Deviations from Mean'' (user specifies N)
- Swap elevations (multiply by -1)
* Swap elevations (multiply by -1)
 
 
 
 
 
Images can be opened in SMS using the ''File'' | '''Open''' menu command. They can also be added to a simulation by dragging and dropping the file into SMS. The images are then added to the image folder in the [[SMS:Project Explorer|Project Explorer]] and displayed in the background to aid in the placement of objects as they are being constructed or simply to enhance visualization of the project domain. All TIFF images are converted to JPEG when they are read in. Multiple images can be imported into SMS.
 
== Exporting Image Files ==
Images (or files related to images) are saved in the following ways:
 
=== Save As ===
The image displayed in the ''Graphics Window'' can be saved as a Bitmap Image File (*.bmp) or JPEG Image File (*.jpg, *.jpeg) using the [[SMS:SMS Menus|''File'' | '''Save As''' menu command]] and specifying an image file as the save as type. The resolution of the saved image is based on the screen resolution and scale factor specified in the [[SMS:Preferences|''Preferences'' dialog]].
 
=== Project File ===
When a project file is saved any images that are part of the project are saved. The registration information is saved in the project file to provide the coordinate system information for the image.
 
=== Copy to Clipboard ===
When the [[SMS:SMS Menus|''Edit'' | '''Copy to Clipboard''' menu command]] is selected, the image currently displayed in the ''Graphics Window'' is copied to the clipboard. This image can then be pasted into reports or other programs by pressing ''CTRL + V''. The resolution of the saved image is based on the screen resolution and scale factor specified in the [[SMS:Preferences|''Preferences'' dialog]].
 
=== Export World File ===
A World File can be exported for the selected image by right-clicking on the [[SMS:Project Explorer|Project Explorer]] and selecting the ''Export World File'' command. A world file is a  special file that contains registration data that can be used to register images.
 
== Geo-Referencing ==
A geo-referenced image includes information specifying the real world size and location of the image. The coordinate system can be embedded in the file or given in a separate file called a world file (for example: a TIFF world file, *.tfw). When geo-referenced image files are opened, SMS automatically registers the image to the real world coordinate location specified. In the case where a separate world file is used, SMS will search for it and register the image if the world file has the same filename prefix as the image file and is in the same folder.
 
If the image file is not geo-referenced then you will have to [[Registering an Image|register the image]] manually. (See [[Registering an Image|Registering an Image]])
 
When the SMS project is saved, a link to the image is saved in the project file, along with the current image registration information so that the image is re-registered to the same coordinates every time the project is opened. The original image file and world file (if one exists) are not altered.
 
== Display Options ==
Image display options are changed in the [[SMS:Project Explorer|Project Explorer]]. Display options include:
* '''Visibility''' – The visibility of an image is turned off by toggling the check box next to the image in the [[SMS:Project Explorer|Project Explorer]].
* '''Transparency''' – The transparency of each image can be changed by right-clicking on the image in the [[SMS:Project Explorer|Project Explorer]] and selecting '''Transparency''' from the right-click menu.
 
== Image Deletion ==
A single image is deleted by right-clicking on the image in the [[SMS:Project Explorer|Project Explorer]] and selecting the '''Delete''' command. To delete all images, you right-click on the Images folder in the [[SMS:Project Explorer|Project Explorer]] and select '''Clear Images'''.
 
== Dynamic Imagery from ArcGIS ==
Starting in SMS 11.0 (32-bit only), dynamic background images can be accessed from the web through ArcGIS. If you have ArcGIS on your computer, you can use the GIS module within SMS to get background imagery that updates on the fly from the internet. To access these images, follow the steps below.
 
#Switch to the GIS module (select the globe in the bottom left of the SMS screen)
#Select “Data | Enable ArcObjects”
#Select “Data | Add Data…”
#Browse to the “C:\Program Files (x86)\SMS 11.0\Supporting Files\GIS Layer Files” directory
#Select the desired layer
#Select “Add”
 
Note: This feature is only available in the SMS 11.0 beta (32-bit). Since this version is still in beta, it should not be used in place of the release version of SMS (SMS 10.1).


== Related Topics ==
== Related Topics ==
* [[Image Pyramids|Image Pyramids]]
* [[Raster_Options|Rasters]]
* [[Import from Web]]
* [[SMS:Scatter_Module|Scatter Module]]
* [[Registering an Image|Registering an Image]]
* [[Data Sources]]




{{Template:Navbox SMS}}
{{Template:Navbox SMS}}
[[Category:Archived]]
[[Category:SMS File Formats|L]]
[[Category:Raster|Lidar]]
[[Category:File Format|Lidar]]
[[Category:External Links]]
[[Category:SMS Import Dialogs|Lidar]]

Latest revision as of 14:17, 10 June 2019

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The term LIDAR refers to a technology known as LIght Detection And Ranging. This technology is used to gather a large amount of survey data from fixed wing aircraft or helicopters as they fly over the survey region. The technique has the ability to penetrate clear water up to a limited depth (maybe up to 20 meters but varies based on conditions).

A LIDAR file (normally it has an extension of ".las" or ".laz") is a survey file that includes data points gathered from a LIDAR system and processed.

Importing a LIDAR File

The LIDAR Load Options dialog

When a lidar is read in, the Lidar Load Options dialog appears to allow the user to specify importing options. Principally, the user specifies whether the data should be loaded as a raster or scatter. Then create a raster or scatter set. The options in the dialog are described as a point cloud (scatter set) or a grid (raster).

This dialog also lists all the data sources/types of data included in the file and allows the user to select which data types should be imported.

Reading as a point cloud (scatter set)

If the user selects point cloud, SMS creates both a scatter set and an image. Note that because this is not a uniformly arranged set of data and thus not a raster, all of the raster editing options will be unavailable for this data. There are several options for the appearance of the image. These include:

  • Use Colors if Present (Elevations Otherwise) – The points in the LIDAR set are given a color. This appears like a contour plot image.
  • Color Elevations Using Current Shader – currently SMS does not allow the user to select shader options, so this option also appears as a contour plot image.
  • Color by intensity – this results in a gray scale image.
  • Color by classification – the points in the LIDAR set are colored based on their type. This can be useful to see what types of data (layers) exist in the file. If all the points in a file are the same type, the image is a single color.
  • Color by random number – colored points – no documentation is available for this feature

The scatter points created when reading a LIDAR file are not triangulated. They must be triangulated to extract observation profiles or use them as source of bathymetry.

Reading as an elevation grid (raster)

If the user selects grid, XMS creates a raster and an image. XMS adds the raster as a VTK raster and the image as an image. The image appears as a hillshade.

This option is much slower than the point cloud option.

Options include:

  • Elevation Grid creation Options – Tight to Loose
    • Loose (default) – for a test case it created 63752617 points/cells
    • Medium – for test case it created 63714287 points/cells with some holes
    • Tight – for test case it created 15058938 points that are mostly disjoint
  • If the LIDAR data is not a box, SMS can fill either the entire box or just the convex hull with gridded data.

Holes left in the grid are also reflected as holes in the image. The tighter the option, the slower the process appears to be.

LIDAR Images

Reading a LIDAR file always results in an image in XMS. For some images, XMS allows the conversion to a RASTER. Since that option is available when reading the LIDAR file, this capability is not available for images created as a side effect of reading a LIDAR file.

General Options

In addition to filtering out point classifications, XMS supports the following options:

  • Use Previous Mode Load Only 1 in Every N Samples (user specifies N)
  • Delete Samples Over N Standard Deviations from Mean (user specifies N)
  • Swap elevations (multiply by -1)

Related Topics


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