Create intensity and points/area-units raster

[Daniel Barona]

Hi LAStools user group:

This group has been so helpful for my formation related with lidar processing! First, I want to create an intensity raster. I've tried using lasgrid but the output always is black with zero values by each pixel.
This is my sentence: lasgrid -i pointcloud.las -step 0.1 -intensity -otif  -o intensity.tif


Second, i want to know if it's possible create an raster that can show me how much points there are, for example, in one square meter, because the point distribution is not always equal in a terreain.

Thanks so much!

Regarts,

Daniel.

[Enzo Campomanes]

For the intensity raster, what I do is I clamp intensities above 255 and also intensities below 0 to keep my values from 0-255 only. Another difference in the sentence I usually use is "-average" and "-fill 15". I add the fill 15 parameter to avoid holes in the resulting raster. I also use the -average parameter since the default operation is -lowest which might explain your black raster. But I'm not so sure since there is no lasinfo report, etc. :)

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Florencio P. Campomanes V

Senior Science Research Specialist, UP Cebu Phil-LiDAR 2

[Martin Isenburg]

Hello,

i assume your software for viewing the TIF file is simply not able to properly display the intensity of a TIF file with a 16 bit channel. Attached is what QGIS displays when I create an intensity grid as follows. Also shown is the gdalinfo output for the resulting grid.

>> lasgrid -i ..\data\fusa.laz -step 1 -intensity -o fusa_1m_intensity.tif

>> gdalinfo.exe fusa_1m_intensity.tif

Driver: GTiff/GeoTIFF

Files: fusa_1m_intensity.tif

       fusa_1m_intensity.tfw

Size is 250, 250

Coordinate System is:

PROJCS["WGS 84 / UTM zone 54S",

    GEOGCS["WGS 84",

        DATUM["WGS_1984",

            SPHEROID["WGS 84",6378137,298.257223563,

                AUTHORITY["EPSG","7030"]],

            AUTHORITY["EPSG","6326"]],

        PRIMEM["Greenwich",0],

        UNIT["degree",0.0174532925199433],

        AUTHORITY["EPSG","4326"]],

    PROJECTION["Transverse_Mercator"],

    PARAMETER["latitude_of_origin",0],

    PARAMETER["central_meridian",141],

    PARAMETER["scale_factor",0.9996],

    PARAMETER["false_easting",500000],

    PARAMETER["false_northing",10000000],

    UNIT["metre",1,

        AUTHORITY["EPSG","9001"]],

    AUTHORITY["EPSG","32754"]]

Origin = (277750.000000000000000,6122500.000000000000000)

Pixel Size = (1.000000000000000,-1.000000000000000)

Metadata:

  AREA_OR_POINT=Area

  TIFFTAG_ARTIST=created by LAStools (c) martin....@rapidlasso.com

  TIFFTAG_SOFTWARE=LAStools is a product of rapidlasso GmbH, Germany

Image Structure Metadata:

  COMPRESSION=LZW

  INTERLEAVE=BAND

Corner Coordinates:

Upper Left  (  277750.000, 6122500.000)

Lower Left  (  277750.000, 6122250.000)

Upper Right (  278000.000, 6122500.000)

Lower Right (  278000.000, 6122250.000)

Center      (  277875.000, 6122375.000)

Band 1 Block=250x20 Type=Int16, ColorInterp=Gray

  NoData Value=-9999 

For your other question see the answer I just gave in this thread:

http://groups.google.com/d/topic/lastools/azlZgD-a2FQ/discussion

Regards,

Martin

[Jennifer Roelens]

Hello,

I'm struggling a bit with the same problem. My intensity data is 16-bit, but is ranging mostly between 0 and 300, the rest are outliers. I tried rescaling between 0 and 255. But I don't really understand what clamping is. I tried to do it between 0 and 255 and I got a nice distribution, but I don't know  if I can just do this 'clamping' or I need to rescale the data by dividing by 256. The data was taken with a Riegl sensor.

I hope somebody can help me.

Thank you in advance!

Jennifer

[Martin Isenburg]

Hello Jennifer,

sorry for the late reply. Slowly working my way back through unanswered emails ... (-:

Clamping means that if your values are higher than the clamp value they will be set *to* the clamp value (e.g. 59 stays 59, 233 stays 233, but 287, 498, and 3823 are all set to 255).

In order to decide how to treat your intensity values it is useful to look at the intensity distribution. For example see the intensity histogram below. For such a distribution where only a very small percentage of values is above 255 I would suggest it is save to clamp the values at 255. This may, of course, be application dependant. If you are trying to find highly-reflective objects you may not want to do this. Below two sample views (attached) that show (only) the intensity values above 255 and then as a greyscale image clamped to 255.

D:\LAStools\bin>lasview -i ..\data\fusa.laz -keep_intensity_above 255

D:\LAStools\bin>lasview -i ..\data\fusa.laz -clamp_intensity_above 255 -color_by_intensity   

D:\LAStools\bin>lasinfo -i ..\data\fusa.laz -nh -nv -nmm -histo intensity 16

lasinfo (160124) report for ..\data\fusa.laz

intensity histogram with bin size 16

  bin [0,16) has 21318

  bin [16,32) has 75230

  bin [32,48) has 46797

  bin [48,64) has 29090

  bin [64,80) has 25188

  bin [80,96) has 34872

  bin [96,112) has 29576

  bin [112,128) has 10472

  bin [128,144) has 2825

  bin [144,160) has 937

  bin [160,176) has 420

  bin [176,192) has 222

  bin [192,208) has 116

  bin [208,224) has 74

  bin [224,240) has 59

  bin [240,256) has 39

  bin [256,272) has 29

  bin [272,288) has 25

  bin [288,304) has 14

  bin [304,320) has 16

  bin [320,336) has 16

  bin [336,352) has 12

  bin [352,368) has 8

  bin [368,384) has 9

  bin [384,400) has 8

  bin [400,416) has 9

  bin [416,432) has 8

  bin [432,448) has 9

  bin [448,464) has 12

  bin [464,480) has 7

  bin [480,496) has 5

  bin [496,512) has 9

  bin [512,528) has 9

  bin [528,544) has 3

  bin [544,560) has 5

  bin [560,576) has 4

  bin [576,592) has 8

  bin [592,608) has 2

  bin [608,624) has 3

  bin [624,640) has 3

  bin [640,656) has 2

  bin [656,672) has 1

  bin [688,704) has 1

  bin [704,720) has 4

  bin [720,736) has 2

  bin [736,752) has 1

  bin [752,768) has 1

  bin [768,784) has 1

  bin [816,832) has 2

  bin [832,848) has 2

  bin [896,912) has 2

  bin [912,928) has 1

  bin [928,944) has 1

  bin [944,960) has 1

  bin [960,976) has 2

  bin [976,992) has 2

  bin [1040,1056) has 1

  bin [1088,1104) has 2

  bin [1104,1120) has 1

  bin [1120,1136) has 1

  bin [1168,1184) has 1

  bin [1216,1232) has 2

  bin [1248,1264) has 2

  bin [1280,1296) has 1

  bin [1344,1360) has 1

  bin [1376,1392) has 3

  bin [1392,1408) has 1

  bin [1408,1424) has 1

  bin [1424,1440) has 1

  bin [1504,1520) has 1

  bin [1568,1584) has 2

  bin [1600,1616) has 1

  bin [1632,1648) has 2

  bin [1648,1664) has 1

  bin [1664,1680) has 1

  bin [1712,1728) has 1

  bin [1728,1744) has 1

  bin [1856,1872) has 1

  bin [1968,1984) has 1

  bin [2064,2080) has 1

  bin [2096,2112) has 1

  bin [2112,2128) has 1

  bin [2224,2240) has 1

  bin [2288,2304) has 1

  bin [2448,2464) has 1

  bin [2528,2544) has 1

  bin [2544,2560) has 1

  bin [2624,2640) has 1

  bin [2656,2672) has 1

  bin [2800,2816) has 1

  bin [2896,2912) has 1

  bin [2912,2928) has 1

  bin [3072,3088) has 1

  bin [3328,3344) has 1

  bin [4032,4048) has 1

  bin [4192,4208) has 1

  bin [4800,4816) has 1

  bin [4816,4832) has 1

  bin [4896,4912) has 1

  bin [5056,5072) has 1

  bin [5088,5104) has 1

  bin [5280,5296) has 1

  bin [5360,5376) has 1

  bin [5472,5488) has 1

  bin [5504,5520) has 1

  bin [5552,5568) has 1

  bin [5600,5616) has 1

  bin [5728,5744) has 1

  bin [6576,6592) has 1

  bin [6768,6784) has 1

  bin [6800,6816) has 2

  bin [7808,7824) has 1

  bin [7824,7840) has 1

  bin [8864,8880) has 1

  bin [8960,8976) has 1

  bin [9376,9392) has 1

  bin [11744,11760) has 1

  bin [12336,12352) has 1

  bin [18288,18304) has 1

  bin [27856,27872) has 1

  bin [35312,35328) has 1

  bin [37104,37120) has 1

  bin [56192,56208) has 1

  bin [56560,56576) has 1

  bin [59728,59744) has 1

  bin [61280,61296) has 1

  bin [62288,62304) has 1

  average intensity 57.722 for 277573 element(s)

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