Notebook: Lukas Winiwarter, 2022
In this demo, we demonstrate how a scanner with multiple scanlines, such as the Velodyne® VLP-16, can be configured in HELIOS++. The demo contains two surveys, one for a static simulation (scanner at a single location) and one for a dynamic simulation (scanner moving between waypoints).
import sys, os
from pathlib import Path
from IPython.display import Code
current_folder = globals()["_dh"][0]
helios_path = str(Path(current_folder).parent)
sys.path.append(helios_path) # add helios-plusplus directory to PATH
import pyhelios
from pyhelios.util.xmldisplayer import display_xml, find_playback_dir
As the scanner is the main component in this demo, we investigate the scanner XML file tls_scanners.xml. Here, we find a predefined Velodyne VLP-16. Other scanners, such as the Velodyne Puck LITE, or the Ouster OS2 can be implemented in similar ways.
os.chdir(helios_path)
Code(display_xml('data/scanners_tls.xml', 'vlp16'))
<scanner id="vlp16" accuracy_m="0.03" beamDivergence_rad="0.0007" name="Velodyne VLP-16" optics="rotating" pulseFreqs_Hz="18750" pulseLength_ns="4" rangeMin_m="0.0100" rangeMax_m="100" scanAngleMax_deg="1" scanAngleEffectiveMax_deg="1" scanFreqMin_Hz="0" scanFreqMax_Hz="0" wavelength_nm="532" headRotatePerSecMax_deg="7200">
<FWFSettings beamSampleQuality="1" /> <!-- set to one for fast simulations -->
<channels>
<channel id="0">
<beamOrigin x="0" y="0" z="0">
<rot axis="x" angle_deg="-15" />
</beamOrigin>
</channel>
<channel id="1">
<beamOrigin x="0" y="0" z="0">
<rot axis="x" angle_deg="1" />
</beamOrigin>
</channel>
<channel id="2">
<beamOrigin x="0" y="0" z="0">
<rot axis="x" angle_deg="-13" />
</beamOrigin>
</channel>
<channel id="3">
<beamOrigin x="0" y="0" z="0">
<rot axis="x" angle_deg="3" />
</beamOrigin>
</channel>
<channel id="4">
<beamOrigin x="0" y="0" z="0">
<rot axis="x" angle_deg="-11" />
</beamOrigin>
</channel>
<channel id="5">
<beamOrigin x="0" y="0" z="0">
<rot axis="x" angle_deg="5" />
</beamOrigin>
</channel>
<channel id="6">
<beamOrigin x="0" y="0" z="0">
<rot axis="x" angle_deg="-9" />
</beamOrigin>
</channel>
<channel id="7">
<beamOrigin x="0" y="0" z="0">
<rot axis="x" angle_deg="7" />
</beamOrigin>
</channel>
<channel id="8">
<beamOrigin x="0" y="0" z="0">
<rot axis="x" angle_deg="-7" />
</beamOrigin>
</channel>
<channel id="9">
<beamOrigin x="0" y="0" z="0">
<rot axis="x" angle_deg="9" />
</beamOrigin>
</channel>
<channel id="10">
<beamOrigin x="0" y="0" z="0">
<rot axis="x" angle_deg="-5" />
</beamOrigin>
</channel>
<channel id="11">
<beamOrigin x="0" y="0" z="0">
<rot axis="x" angle_deg="11" />
</beamOrigin>
</channel>
<channel id="12">
<beamOrigin x="0" y="0" z="0">
<rot axis="x" angle_deg="-3" />
</beamOrigin>
</channel>
<channel id="13">
<beamOrigin x="0" y="0" z="0">
<rot axis="x" angle_deg="13" />
</beamOrigin>
</channel>
<channel id="14">
<beamOrigin x="0" y="0" z="0">
<rot axis="x" angle_deg="-1" />
</beamOrigin>
</channel>
<channel id="15">
<beamOrigin x="0" y="0" z="0">
<rot axis="x" angle_deg="15" />
</beamOrigin>
</channel>
</channels>
</scanner>
The scanner is defined with rotating optics, but the values for scanFreqMin_Hz and scanFreqMax_Hz (both "0") show that this feature is not used in this implementation. Additionaly, the scanAngleMax_deg is set to a value of 1. Subsequently, 16 channels are defined, each with their individual rotations. As the scan plane is not used (default would be the y/z-Plane, see the wiki) and only a single direction per pulse is given, a simple rotation upwards or downwards about the x axis is sufficient. The values for the angles are taken from the user manual of the VLP-16 (pages 54-55).
The pulseFreq_hz in the <scannerSettings > is coming from the max. measurement rate of the VLP-16 (300,000 pts/sec). The headRotatePerSecMax_deg value corresponds to what Velodyne refers to as scan frequency - this is not to be confused with the within-scan line scanFreq_hz we use for e.g. RIEGL-type TLS sensors. The user manual gives a value of 1200 rpm as a maximum rotation speed of the motor, equivalent to 20 rotations per seconds (20 Hz scan frequency), or a rotation speed headRotatePerSecMax_deg of 7200 (20 * 360deg).
Let us now use a simple scene (just containing a cube with 100 m side length, centered around the origin) to carry out two surveys:
Code(display_xml('data/surveys/demo/box_survey_static_puck.xml'))
<document>
<scannerSettings id="scaset" active="true" pulseFreq_hz="18750" scanFreq_hz="0" />
<survey name="box_puck_static" scene="data/scenes/demo/box_scene.xml#box_scene" platform="data/platforms.xml#tripod" scanner="data/scanners_tls.xml#vlp16">
<leg>
<platformSettings x="0" y="0" z="0" />
<scannerSettings template="scaset" headRotatePerSec_deg="3600" headRotateStart_deg="0" headRotateStop_deg="3600" /> <!-- 1 second integration time -->
</leg>
</survey>
</document>
Here, we note two things:
the value of headRotatePerSec_deg, which here corresponds to 10 rotations per second, or 600 rotations per minute. The user manual explains that values between 300 and 1200 rpm, in increments of 60 rpm, are permissible.
the range between headRotateStart_deg and headRotateStop_deg. Combined with the rotation speed, this gives the sensor's integration time. In this example, 10 full rotations (10 * 360 deg) are carried out, which takes (at a rotation speed of 10 rotations per second or 3600 deg per second) one second. We are now ready to
!"run/helios" data/surveys/demo/box_survey_static_puck.xml -q
Now let's find the output files and display a 3D plot for all points recorded in the first 1/10th second (one rotation). You can see how the 'zero' location of the scanner is towards the positive Y-axis.
import numpy as np
import pandas as pd
import matplotlib.pyplot as plt
import matplotlib as mpl
output_path = find_playback_dir("data/surveys/demo/box_survey_static_puck.xml")
print("Loading points from", Path(output_path).relative_to(helios_path).as_posix())
SP1 = pd.read_csv(Path(output_path) / 'leg000_points.xyz',
names="X Y Z intensity echoWidth returnNumber numberOfReturns fullwaveIndex hitObjectId class gpsTime".split(' '),
delimiter=' ')
SP_filtered = SP1[SP1['gpsTime'] <= min(SP1['gpsTime']) + 0.1] # select all points recorded in the first 1/10 second
fig = plt.figure(figsize=(15,10))
ax = fig.add_subplot(projection='3d')
ax.scatter(SP_filtered['X'], SP_filtered['Y'], SP_filtered['Z'], s=0.1, c=SP_filtered['gpsTime'])
ax.scatter([0], [0], [0], s=50, c='red')
ax.set_xlabel('X')
ax.set_ylabel('Y')
ax.set_zlabel('Z')
ax.tick_params(labelsize=16)
plt.show()
Loading points from output/box_puck_static/2023-02-27_09-20-29