How to change values in a LAS file using the ENVI Lidar programming interface (API)

ENVI LiDAR is an interactive geospatial software environment that lets you create realistic 3D visualizations and easily extract important features and products from raw LiDAR point cloud data. The elevation information contained within LiDAR can be used to create Digital Elevation Models (DEMs), or be included in your geospatial products like line-of-sight or right-of way analyses.

Occasionally, it might be desirable to alter the values contained in a Lidar .LAS format file such as elevation (z) or attribute (RGB, class).  ENVI LiDAR's API can be used to edit and write out a new .LAS file with the desired changes.  The following code examples alter the data within a .LAS file by 1) adding a constant value to the elevations within the file and 2) setting the RGB value of a classified .LAS.  The first example code uses the sample .LAS dataset that is contained in the ENVI LiDAR distribution. The second example uses a classified .LAS file.

;-------------------------------

; Example code that changes the elevation (z) values in a .LAS file by adding a constant

PRO AddConstantZValue

  COMPILE_OPT idl2

  e = e3de(/headless)

  lasFileName = 'C:\ProgramFiles\Exelis\ENVILiDAR51\DataSample\DataSample.las'

  ;Directly read the input LAS filecontaining classification values

  oLidar = e.openlidar(lasFileName,/DIRECT_READ)  

  startIndex = 0

  blockSize = 500000

  allClass = MAKE_ARRAY(blockSize, /BYTE)

  increaseZby = 10  

  ; create the E3DLidarWriter

  outFileName = 'C:\Temp\IncreasedZby10.las'

  writer = E3DLidar(outFileName,/OVERWRITE)

    allread = 0

  ;Cycle through the points

  WHILE (allread eq 0) DO BEGIN

    pointsInRange = oLidar.GetPointsInRange(startIndex,blockSize, $

                           ALL_ATTRIBS=ALL_ATTRIBS, $

                           COUNT=nPointsRead)

    ;increase the z value byincreaseZby

    pointsInRange[2,*] = pointsInRange[2,*] + increaseZby

    ;write the updatedpoint values and all attributes

    writer.WritePoints, pointsInRange,ALL_ATTRIBS=all_attribs

    startIndex += nPointsRead

    IF (nPointsRead LT blocksize) THEN allread = 1

  ENDWHILE

  ;Save and close output LAS file

  writer.SAVE

  writer.CLOSE

  e.CLOSE

END

;--------------------------

; Example code that changes an attribute value in a .LAS file by assigning an RGB value to a class

PRO setRGBbyLASclass

  COMPILE_OPT idl2

  e = e3de(/headless)

 

 ;Specify the classified input LASfile name

  lasFileName = 'C:\temp\classifiedPointcloud.las'

  ;Directly read (don’t create a project) the input LAS file containing classification values

  oLidar = e.openlidar(lasFileName,/DIRECT_READ)

  startIndex = 0

  blockSize = 500000

  allClass = MAKE_ARRAY(blockSize, /BYTE)

  ; create the output file

  outFileName = FILE_DIRNAME(lasFileName) + '\RGBbyClassification.las'

  writer = E3DLidar(outFileName,/OVERWRITE)

  allread = 0

  ;Cycle through the points, setting the RGBvalue based on

  ;classification values of the points

  WHILE (allread eq 0) DO BEGIN

    pointsInRange = oLidar.GetPointsInRange(startIndex,blockSize, $

                           ALL_ATTRIBS=ALL_ATTRIBS, $

                           COUNT=nPointsRead)

   ;*ALL_ATTRIBS.CLASSIFICATIONS returns the classification codes stored in

    ; the las file

    inClass = *ALL_ATTRIBS.CLASSIFICATIONS

    IF (nPointsRead LT blocksize) THEN allread = 1

    allClass =[allClass,inClass]

    uniqAllClass = allClass[UNIQ(allClass, SORT(allClass))]

    rgb = MAKE_ARRAY(3,nPointsRead, /BYTE)

    FOREACH i, uniqAllClass DO BEGIN

      CASE i OF

        ;Unprocessed

        0: BEGIN

            index = WHERE(inClass EQ 0)

            red=190

            green=190

            blue=190

            rgb[0,index] = red

            rgb[1,index] = green

            rgb[2,index] = blue

          END

       ;Unclassified

        1: BEGIN

            index = WHERE(inClass EQ 1)

            red=255

            green=255

            blue=255

            rgb[0,index] = red

            rgb[1,index] = green

            rgb[2,index] = blue

          END

        ;Terrain

        2: BEGIN

            index = WHERE(inClass EQ 2)

            red=255

            green=177

            blue=100

            rgb[0,index] = red

            rgb[1,index] = green

            rgb[2,index] = blue

          END

        ;Near Terrain

        3: BEGIN

            index = WHERE(inClass EQ 3)

            red=128

            green=255

            blue=0

            rgb[0,index] = red

            rgb[1,index] = green

            rgb[2,index] = blue

          END

        ;Trees

        5: BEGIN

            index = WHERE(inClass EQ 5)

            red=0

            green=147

            blue=0

            rgb[0,index] = red

            rgb[1,index] = green

            rgb[2,index] = blue

          END

        ;Buildings

        6: BEGIN

            index = WHERE(inClass EQ 6)

            red=217

            green=217

            blue=0

            rgb[0,index] = red

            rgb[1,index] = green

            rgb[2,index] = blue

          END

       ;Power lines

        14: BEGIN

             index = WHERE(inClass EQ 14)

             red=255

             green=100

             blue=255

             rgb[0,index] = red

             rgb[1,index] = green

             rgb[2,index] = blue

           END

        ;Power poles

        15: BEGIN

             index = WHERE(inClass EQ 15)

             red=160

             green=80

             blue=0

             rgb[0,index] = red

             rgb[1,index] = green

             rgb[2,index] = blue

           END

        ELSE: PRINT, 'Bad value'

      ENDCASE

    ENDFOREACH

    writer.WritePoints, pointsInRange,ALL_ATTRIBS=all_attribs, RGB=rgb

    startIndex += nPointsRead

  ENDWHILE

  ;Save and close output LAS file

  writer.SAVE

  writer.CLOSE

  e.CLOSE

END

Reviewed 8/25/2014 MM