Image Intensity

[Dennis Bernardi]

Martin,

 

I again, hehe

 

When I used lasgrid to create Imagem Intenstity, this image is created with 16 or 32bits

 

las2dem –i *.laz –intensity 1.5 –use_tile_bb  -olaz –nbits 16 (or 32) –odix _Intensity –step 0.5

lasgrid –i *_intensity.laz –merged –step 0.5 –o intensity.tif

 

If I write

 

las2dem –i *.laz –intensity 1.5 –use_tile_bb  -olaz –nbits 8  –step 0.5

they return this error: warning: nbits 8 for 16 bits intensity output there were 9999 clipped rasters

 

How is possible to create Intensity Images with 8Bits?

 

 

Dennis Bernardi

Coordenador Corporativo

Cadastro e Geoprocessamento

dennis....@fibria.com.br

Cel 55 12  99704 5301

Tel 55 12 2128 1480

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www.fibria.com.br

 

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[Martin Isenburg]

Hello,

yes, it is possible to create 8 bit gray or false color images that represent the 16 bit intensity channel in lasgrid, las2dem, and blast2dem. By default the *actual* 16 bit values are gridded / interpolated onto the raster. To map these 16 bit values to an 8 bit gray (or false color) image you need to specify '-gray' (or '-false'). Then the minimal value will be mapped to black (or blue) and the maximal value to white (or red) based on the range in each file. For a large tiling this will give different ranges for each file and an incoherent look. Also if there are a few outliers because reflective surfaces then most of the pixels will be black (or blue). The recommended practice is to specify a '-set_min_max 0 255' or '-set_min_max 100 1000' range that maps all intensities within the same range to the back-white ramp (or blue-red color ramp). A good way to get an idea what a reasonable range is for your LiDAR is to look at the distribution of intensities with lasinfo. This example here shows that a linear min/max range is a bad idea. We choose min max ranges [0,255],  [0,127], and [0,63] to show the differences:

lasgrid -i ..\data\fusa.laz -intensity -highest -gray -set_min_max 0 255 -odix _int_gray_0_255 -opng

lasgrid -i ..\data\fusa.laz -intensity -highest -gray -set_min_max 0 127 -odix _int_gray_0_127 -opng

lasgrid -i ..\data\fusa.laz -intensity -highest -gray -set_min_max 0  63 -odix _int_gray_0_063 -opng

lasgrid -i ..\data\fusa.laz -intensity -highest -false -set_min_max 0 255 -odix _int_false_0_255 -opng

lasgrid -i ..\data\fusa.laz -intensity -highest -false -set_min_max 0 127 -odix _int_false_0_127 -opng

lasgrid -i ..\data\fusa.laz -intensity -highest -false -set_min_max 0  63 -odix _int_false_0_063 -opng

The resulting images are attached.

lasinfo -i ..\data\fusa.laz -nh -nv -nmm -nr -histo intensity 64

lasinfo (181119) report for '..\data\fusa.laz'

intensity histogram with bin size 64.000000

  bin [0,64) has 172435

  bin [64,128) has 100108

  bin [128,192) has 4404

  bin [192,256) has 288

  bin [256,320) has 84

  bin [320,384) has 45

  bin [384,448) has 34

  bin [448,512) has 33

  bin [512,576) has 21

  bin [576,640) has 16

  bin [640,704) has 4

  bin [704,768) has 8

  bin [768,832) has 3

  bin [832,896) has 2

  bin [896,960) has 5

  bin [960,1024) has 4

  bin [1024,1088) has 1

  bin [1088,1152) has 4

  bin [1152,1216) has 1

  bin [1216,1280) has 4

  bin [1280,1344) has 1

  bin [1344,1408) has 5

  bin [1408,1472) has 2

  bin [1472,1536) has 1

  bin [1536,1600) has 2

  bin [1600,1664) has 4

  bin [1664,1728) has 2

  bin [1728,1792) has 1

  bin [1856,1920) has 1

  bin [1920,1984) has 1

  bin [2048,2112) has 2

  bin [2112,2176) has 1

  bin [2176,2240) has 1

  bin [2240,2304) has 1

  bin [2432,2496) has 1

  bin [2496,2560) has 2

  bin [2624,2688) has 2

  bin [2752,2816) has 1

  bin [2880,2944) has 2

  bin [3072,3136) has 1

  bin [3328,3392) has 1

  bin [4032,4096) has 1

  bin [4160,4224) has 1

  bin [4800,4864) has 2

  bin [4864,4928) has 1

  bin [5056,5120) has 2

  bin [5248,5312) has 1

  bin [5312,5376) has 1

  bin [5440,5504) has 1

  bin [5504,5568) has 2

  bin [5568,5632) has 1

  bin [5696,5760) has 1

  bin [6528,6592) has 1

  bin [6720,6784) has 1

  bin [6784,6848) has 2

  bin [7808,7872) has 2

  bin [8832,8896) has 1

  bin [8960,9024) has 1

  bin [9344,9408) has 1

  bin [11712,11776) has 1

  bin [12288,12352) has 1

  bin [18240,18304) has 1

  bin [27840,27904) has 1

  bin [35264,35328) has 1

  bin [37056,37120) has 1

  bin [56192,56256) has 1

  bin [56512,56576) has 1

  bin [59712,59776) has 1

  bin [61248,61312) has 1

  bin [62272,62336) has 1

  average intensity 57.721968635277925 for 277573 element(s)

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