Extract the points in the overlap between flight lines..

[MAG]

I have multiple tiled Las files and need to extract the points in the
overlap. In all i have 49 tiles, just classified as ground and other
points. I have no idea how to extract the point in the overlap
between the overlap. I need them for som stripadjustment chek. How can
i do that, eny suggestions? Any help would be appriciated..

[Martin Isenburg]

Hello,

Morton and me have worked out his work-flow off-line. There are two
answers depending on whether the work-flow should be per tile or for
the whole data set in one piece.

Here the work-flow per tile:

(1) run lasinfo on the example tile "62046-06.las" and print the
point_source_ID histogram (aka flight line info)

lasinfo -i tiles\62046-06.las -no_header -no_minmax -histo
point_source 1
point source id histogram with bin size 1
bin 23024 has 740168
bin 23025 has 1288240
bin 23026 has 504029

so we have three flight lines named 23024, 23025, and 23026

(2) get the boundary polygons for the three flight lines of tile
"62046-06.las"

lasboundary -i tiles\62046-06.las -keep_point_source 23024 -o tiles
\62046-06_23024.shp
lasboundary -i tiles\62046-06.las -keep_point_source 23025 -o tiles
\62046-06_23025.shp
lasboundary -i tiles\62046-06.las -keep_point_source 23026 -o tiles
\62046-06_23026.shp

(3) clip the tile "62046-06.las" minus flight line 23024 against the
boundary polygon of flight line 23024 and view the result

lasclip -i tiles\62046-06.las -drop_point_source 23024 -poly tiles
\62046-06_23024.shp -o tiles\62046-06_overlap23024.las
lasview -i tiles\62046-06_overlap23024.las

(4) clip the tile "62046-06.las" minus flight lines 23025 against the
boundary polygon of flight line 23025 and view the result

lasclip -i tiles\62046-06.las -drop_point_source 23025 -poly tiles
\62046-06_23025.shp -o tiles\62046-06_overlap23025.las
lasview -i tiles\62046-06_overlap23025.las

(5) clip the tile "62046-06.las" minus flight lines 23026 against the
boundary polygon of flight line 23026 and view the result

lasclip -i tiles\62046-06.las -drop_point_source 23026 -poly tiles
\62046-06_23026.shp -o tiles\62046-06_1_overlap23026.las
lasview -i tiles\62046-06_overlap23026.las

i guess automation would be nice ... (-:

cheers,

martin @lastools

[Martin Isenburg]

Hello again.

here the work-flow for the whole data set in one piece (at the example
of 12 tiles):

(1) run lasinfo on the merged set of 12 tiles and print the

point_source_ID histogram (aka flight line info)

lasinfo -i tiles\*.las -merged -no_header -no_minmax -histo

point_source 1
point source id histogram with bin size 1

bin 23022 has 1703567
bin 23023 has 3487026
bin 23024 has 3305249
bin 23025 has 3298939
bin 23026 has 3967651
bin 23027 has 4118496
bin 23028 has 3994599
bin 23029 has 4119683
bin 23030 has 1065201

so we have 9 flight lines numbered 23022 to 23030

(2) run the newest tool "lassplit.exe" on the folder of tiles to
extract the individual flight lines

lassplit -v -i tiles\*.las -merged -v -o tiles\flightlines.las
reading 29060411 points of type 1 from 'tiles\61946-64_1.las'.
creating output file 'tiles\flightlines.23024.las'
creating output file 'tiles\flightlines.23022.las'
creating output file 'tiles\flightlines.23023.las'
creating output file 'tiles\flightlines.23025.las'
creating output file 'tiles\flightlines.23026.las'
creating output file 'tiles\flightlines.23027.las'
creating output file 'tiles\flightlines.23028.las'
creating output file 'tiles\flightlines.23029.las'
creating output file 'tiles\flightlines.23030.las'
split 'tiles\61946-64_1.las' into 9 files. took 114.61 sec.

(3) create a boundary polygon for each of the nine flight lines

lasboundary -i tiles\flightlines*.las -oshp

(4) look at the resulting flight lines with the GUI and notice that
only consecutively numbered flight lines overlap

lasview -i tiles\flightlines*.las -gui

(5) hence, instead of clipping every flight line boundary polygon
against every flight line, clip only those adjacent flight lines where
we know that there is overlap:

first on one side

lasclip -i tiles\flightlines.23022.las -poly
tiles\flightlines.23023.shp -o tiles\flightlines.23022_23023.las
lasclip -i tiles\flightlines.23023.las -poly
tiles\flightlines.23024.shp -o tiles\flightlines.23023_23024.las
lasclip -i tiles\flightlines.23024.las -poly
tiles\flightlines.23025.shp -o tiles\flightlines.23024_23025.las
...

then on the other side

lasclip -i tiles\flightlines.23023.las -poly
tiles\flightlines.23022.shp -o tiles\flightlines.23023_23022.las
lasclip -i tiles\flightlines.23024.las -poly
tiles\flightlines.23023.shp -o tiles\flightlines.23024_23023.las
lasclip -i tiles\flightlines.23025.las -poly
tiles\flightlines.23024.shp -o tiles\flightlines.23025_23024.las
...

for every flight line we now have two files that contain the points of
overlap with the neighboring flight lines on both sides, except for
23022 and 23030 which are the end flight lines and have only overlap
on one side.

regards,

martin @lastools

[Hans Karl Heidemann]

Because this method (which btw, is about as easy as it gets) is so appealing (j/k), LAS v1.4 has a specific Bit Flag for the "overage" points of each swath.

We can only hope that all lidar customers will demand that these points be properly identified and marked by their data vendors, for all projects, from this day forward.

H Karl Heidemann, GISP
Physical Scientist, Lidar Science
U.S. Geological Survey
Earth Resources Observation and Science Center
47914 252nd Street, Sioux Falls, SD 57198
Phn: 605-594-2861
Fax: 605-594-6529
kheid...@usgs.gov
http://lidar.cr.usgs.gov

 "Nothing matters very much, and few things ... matter at all."
                                                                -- Arthur James Balfour

 

 

From:	Martin Isenburg <martin....@gmail.com>
To:	LAStools - efficient tools for LIDAR processing <last...@googlegroups.com>
Date:	01/17/2012 09:26 AM
Subject:	[LAStools] Re: Extract the points in the overlap between flight lines..
Sent by:	last...@googlegroups.com

---

--
Download LAStools at
http://lastools.org/
Visit the LAStools group at
http://groups.google.com/group/lastools/
Be social with LAStools at
http://www.facebook.com/LAStools
http://www.twitter.com/LAStools