Accessing 3-D point cloud data in IDL using the ENVI PointCloud API
Anonym
The following is an example of using the new PointCloud API
included in ENVI 5.3. This allows easy access to 3-D data stored in LAS format. The data and
metadata becomes accessible from IDL. The new API includes ability to read as
well as write 3-D point cloud data in LAS format (there is also much more functionality included beyond that). There are 2 fundamentally
different ways to get read access. One method is to simply read the points in
the order they were stored in the LAS file. This would normally be the order
the points were collected by the LiDAR sensor, although point cloud data could
also be derived from other sources. The second way to access the point cloud
data is by creating an ENVIPointCloud project, which means that the points will
be spatially sorted such that they can be indexed quickly based on spatial
tiles. The sorting process takes a little time initially, but once that is
done, points can be retrieved quickly based on spatial querying methods.
This first example shows how to access point cloud data
using the simple, non-sorted API calls.
ENVI> nv = envi(/current)
ENVI> pc=nv.QueryPointCloud('C:\Users\borsholm\Downloads\Lincoln.laz')
ENVI> print,pc
ENVIPOINTCLOUDQUERY <717772>
DATA_RANGE = 692204.97, 4519668.7,
340.79242, 695331.36, 4522642.4, 485.24673
NPOINTS = 9278073
SPATIALREF = !NULL
URI = 'C:\Users\borsholm\Downloads\Lincoln.laz'
ENVI> pc.metadata
ENVIPOINTCLOUDMETADATA <718218>
File Creation Day = 0
File Creation Year = 0
File Source ID = 0
Generating Software = 'Lidar Explorer by ProLogic, Inc.'
Global Encoding = 0
Max X = 695331.36
Max Y = 4522642.4
Max Z = 485.24673
Min X = 692204.97
Min Y = 4519668.7
Min Z = 340.79242
Number Of Point Records = 9278073
Number Of Variable Length = 3
Point Data Format = 0
Point Data Record Length = 20
Project ID GUID Data 1 = 0
Project ID GUID Data 2 = 0
Project ID GUID Data 3 = 0
Project ID GUID Data 4 = 0, 0, 0, 0, 0, 0, ...
System Identifier = ''
Version Major = 1
Version Minor = 0
X Scale Factor = 1.4558386e-006
X Offset = 692204.97
Y Scale Factor = 1.3847266e-006
Y Offset = 4519668.7
Z Scale Factor = 6.7266782e-008
Z Offset = 340.79242
ENVI> pts=pc.GetPointsInRange(0,pc.npoints,intensity=i)
ENVI> help,pts,i
PTS DOUBLE = Array[3, 9278073]
I UINT = Array[9278073]
ENVI> pc.Close
This shows how get access to metadata associated with the
file, and to return the points as a 3xN array, in the original order that they
were stored in the file.
This second example shows how to spatially sort the points
in a new project, and access points in a given rectangle.
ENVI> pc = nv.OpenPointCloud('C:\Users\borsholm\Downloads\Lincoln.laz')
ENVI> pts = pc.GetPointsInRect(694000, 4520000, 695000, 4521000)
ENVI> help,pts
PTS DOUBLE = Array[3, 1000002]
ENVI> pc.Close