Notebook

Scene Part Swap: Repeated Surveys over Several Scene States¶

Notebook: Hannah Weiser, 2024

This notebook demonstrates how to use the scene swap feature in HELIOS++ both for a terrestrial laser scanning (TLS) and UAV-based laser scanning (ULS) example. In the HELIOS++ scene XML, swaps can be defined for each scene part, resulting in a sequence of different scene states. HELIOS++ will automatically repeat the survey for each scene state.

We will use the command-line access of HELIOS++ to run the simulation, and use Python just for displaying the input XMLs and the resulting point clouds.

In [1]:

from pathlib import Path
from IPython.display import Code
from pyhelios.util.xmldisplayer import display_xml, find_playback_dir
import laspy
import numpy as np
import matplotlib.pyplot as plt
import matplotlib as mpl

In [2]:

import os
os.chdir("..")

TLS¶

Survey¶

The survey consists of two flight lines from a height of 400 m, placed 200 m apart. The scanner is a Leica ALS-50.

In [3]:

Code(display_xml('./data/surveys/dyn/als_dyn_geom_swap.xml'), language='XML')

Out[3]:

<document>
    <survey name="dyn_geom_swap_als" scene="data/scenes/dyn/dyn_geom_swap_scene.xml#dyn_geom_swap_scene" platform="data/platforms.xml#sr22" scanner="data/scanners_als.xml#leica_als50">
		<leg>
            <platformSettings x="100" y="100.0" z="400" onGround="false" movePerSec_m="5" />
            <scannerSettings active="true" pulseFreq_hz="83000" scanFreq_hz="70" scanAngle_deg="60" trajectoryTimeInterval_s="0.01" />
        </leg>
		<leg>
            <platformSettings x="-100" y="-100.0" z="400" onGround="false" movePerSec_m="5" />
            <scannerSettings active="false" pulseFreq_hz="83000" scanFreq_hz="70" scanAngle_deg="60" />
        </leg>
		<leg>
            <platformSettings x="-100" y="100.0" z="400" onGround="false" movePerSec_m="5" />
            <scannerSettings active="true" pulseFreq_hz="83000" scanFreq_hz="70" scanAngle_deg="60" trajectoryTimeInterval_s="0.01" />
        </leg>
		<leg>
            <platformSettings x="100" y="-100.0" z="400" onGround="false" movePerSec_m="5" />
            <scannerSettings active="false" pulseFreq_hz="83000" scanFreq_hz="70" scanAngle_deg="60" />
        </leg>
    </survey>
</document>

Scene¶

The scene consists of three scene parts and has a total of four swaps. Based on the definition, the output of the loops will be as follows:

Loop 1:

small cube
sphere
small cube 2

Loop 2:

sphere
big cube
mid cube

Loop 3:

sphere
nothing
big cube

Loop 4:

big cube
nothing
bigger cube

In [4]:

Code(display_xml('data/scenes/dyn/dyn_geom_swap_scene.xml', 'dyn_geom_swap_scene'))

Out[4]:

<scene id="dyn_geom_swap_scene" name="DynGeomSwapScene">


		<!-- Ground plane -->
		<!-- ************ -->
		<part id="1">
            <filter type="objloader">
                <param type="string" key="filepath" value="data/sceneparts/basic/groundplane/groundplane.obj" />
            </filter>
            <filter type="scale">
                <param type="double" key="scale" value="120" />
            </filter>
			<filter type="translate">
				<param type="vec3" key="offset" value="50.0;0;0" />
			</filter>
        </part>




		<!-- Small cube goes sphere for two repetitions then goes big cube -->
		<!-- ************************************************************* -->
		<part id="2">
            <filter type="objloader">
                <param type="string" key="filepath" value="data/sceneparts/toyblocks/cube.obj" />
            </filter>
			<filter type="rotate">
				<param key="rotation" type="rotation">
					<rot angle_deg="45" axis="z" />
				</param>
			</filter>
			<filter type="scale">
                <param type="double" key="scale" value="0.75" />
            </filter>
			<filter type="translate">
				<param type="vec3" key="offset" value="-40.0;-50.0;0" />
			</filter>
			<!-- Swap small cube by sphere -->
			<swap swapStep="2">
				<filter type="objloader">
                	<param type="string" key="filepath" value="data/sceneparts/toyblocks/sphere.obj" />
		        </filter>
				<filter type="scale">
		            <param type="double" key="scale" value="1.25" />
		        </filter>
				<filter type="translate">
					<param type="vec3" key="offset" value="-30.0;-60.0;0" />
				</filter>
			</swap>
			<!-- Swap sphere by big cube -->
			<swap swapStep="1">
				<filter type="objloader">
		            <param type="string" key="filepath" value="data/sceneparts/toyblocks/cube.obj" />
		        </filter>
				<filter type="rotate">
					<param key="rotation" type="rotation">
						<rot angle_deg="45" axis="z" />
					</param>
				</filter>
				<filter type="scale">
		            <param type="double" key="scale" value="1.5" />
		        </filter>
				<filter type="translate">
					<param type="vec3" key="offset" value="-20.0;-60.0;0" />
				</filter>
			</swap>
        </part>




		<!-- Sphere goes cube goes nothing -->
		<!-- ***************************** -->
		<part id="3">
			<filter type="objloader">
                <param type="string" key="filepath" value="data/sceneparts/toyblocks/sphere.obj" />
            </filter>
			<filter type="scale">
                <param type="double" key="scale" value="1.25" />
            </filter>
			<filter type="translate">
				<param type="vec3" key="offset" value="-10.0;-20.0;0" />
			</filter>
			<!-- Swap sphere by cube -->
			<swap>
				<filter type="objloader">
		            <param type="string" key="filepath" value="data/sceneparts/toyblocks/cube.obj" />
		        </filter>
				<filter type="scale">
		            <param type="double" key="scale" value="2.0" />
		        </filter>
				<filter type="translate">
					<param type="vec3" key="offset" value="-40.0;40.0;0" />
				</filter>
			</swap>
			<!-- Swap cube by nothing -->
			<swap force_null="true">
			</swap>
		</part>




		<!-- Small cube goes mid goes big goes bigger -->
		<!-- **************************************** -->
		<part id="4">
            <filter type="objloader">
                <param type="string" key="filepath" value="data/sceneparts/toyblocks/cube.obj" />
            </filter>
			<filter type="rotate">
				<param key="rotation" type="rotation">
					<rot angle_deg="45" axis="z" />
				</param>
			</filter>
			<filter type="scale">
                <param type="double" key="scale" value="0.75" />
            </filter>
			<filter type="translate">
				<param type="vec3" key="offset" value="-20.0;10.0;0" />
			</filter>
			<!-- Swap small cube by mid cube -->
			<swap swapStep="1">
				<filter type="rotate">
					<param key="rotation" type="rotation">
						<rot angle_deg="45" axis="z" />
					</param>
				</filter>
				<filter type="scale">
		            <param type="double" key="scale" value="2.0" />
		        </filter>
				<filter type="translate">
					<param type="vec3" key="offset" value="-22.0;12.0;0" />
				</filter>
			</swap>
			<!-- Swap mid cube by big cube -->
			<swap swapStep="1">
				<filter type="rotate">
					<param key="rotation" type="rotation">
						<rot angle_deg="45" axis="z" />
					</param>
				</filter>
				<filter type="scale">
		            <param type="double" key="scale" value="3.0" />
		        </filter>
				<filter type="translate">
					<param type="vec3" key="offset" value="-18.0;11.0;0.0" />
				</filter>
			</swap>
			<!-- Swap big cube by bigger cube -->
			<swap swapStep="1">
				<filter type="rotate">
					<param key="rotation" type="rotation">
						<rot angle_deg="45" axis="z" />
					</param>
				</filter>
				<filter type="scale">
		            <param type="double" key="scale" value="3.5" />
		        </filter>
				<filter type="translate">
					<param type="vec3" key="offset" value="-42.0;12.0;0.0" />
				</filter>
			</swap>
        </part>
    </scene>

Executing the Simulation¶

To run the simulation in Jupyter Notebooks, we can use the !command syntax, but you can also just run it from the command line. To get the output as a "laz" file, we also specify --lasOutput and --zipOutput. We also set the --rebuildScene flag, because HELIOS++ rewrites the binary .scene file for each swap iteration. If we had run the survey before and did had set this flag, HELIOS++ would just use the existing scene file and perform only one simulation (the last one from the previous run).

In [5]:

!helios data/surveys/dyn/als_dyn_geom_swap.xml --lasOutput --zipOutput --rebuildScene -q

The results¶

Now let's find the output files, load it, and visualize it. Since we performed several simulations, we have several output folders, four in total.

In [6]:

# get the last four folders that were written for this survey
output_path = find_playback_dir(r"data/surveys/dyn/als_dyn_geom_swap.xml")
folders_sorted = sorted(Path(output_path).parent.glob('*'))[-4:]

In [7]:

def read_pc(path, pt_src_id):
    las = laspy.read(path)
    pc = np.array([las.x, las.y, las.z]).T
    object_id = las['hitObjectId']
    pt_src_id = np.repeat(pt_src_id, pc.shape[0])

    return pc, object_id, pt_src_id

def load_and_merge(pc_folder):
    print('Loading points from', Path(pc_folder).relative_to(os.getcwd()))

    pcs = []
    obj_ids = []
    pt_src_ids = []

    for i, file in enumerate(Path(pc_folder).glob('*.laz')):
        pc, object_id, pt_src_id = read_pc(file, pt_src_id=i)
        pcs.append(pc)
        obj_ids.append(object_id)
        pt_src_ids.append(pt_src_id)
        
    print('Merging files')
    try:
        pc_merged = np.vstack(pcs)
        object_id_merged = np.hstack(obj_ids)
        pt_src_id_merged = np.hstack((pt_src_ids))
    except ValueError:
        print('No points found in folder')
        pc_merged = np.array([])
        object_id_merged = np.array([])
        pt_src_id_merged = np.array([])

    return pc_merged, object_id_merged, pt_src_id_merged

In [8]:

sim_dict = {'name': [],
            'pcs': [],
            'object_ids': [],
            'pt_src_ids': []}
for i, folder in enumerate(folders_sorted):
    pc, obj_id, pt_src_id = load_and_merge(folder)
    sim_dict['name'].append(folder.name)
    sim_dict['pcs'].append(pc)
    sim_dict['object_ids'].append(obj_id)
    sim_dict['pt_src_ids'].append(pt_src_id)

Loading points from output\dyn_geom_swap_als\2024-12-05_18-28-58
Merging files
Loading points from output\dyn_geom_swap_als\2024-12-05_18-29-11
Merging files
Loading points from output\dyn_geom_swap_als\2024-12-05_18-29-34
Merging files
Loading points from output\dyn_geom_swap_als\2024-12-05_18-29-56
Merging files

After loading the point clouds from file, we can now plot the four epochs from the four swaps.

In [9]:

# create figure with 4 panels and 3d axes
fig = plt.figure(figsize=(12, 12))
last_pc = sim_dict['pcs'][-1]
box = (np.ptp(last_pc[:, 0]), np.ptp(last_pc[:, 1]), np.ptp(last_pc[:, 2]))

# color map configuration
lower = 0
upper = 3
n = 4
cmap = mpl.colors.LinearSegmentedColormap.from_list('sceneparts', ['royalblue', 'cyan', 'yellow', 'orange'], N=n)
cmap._init()
norm = mpl.colors.Normalize()
deltac = (upper-lower)/(2*(n-1))

for i, (pc, obj_id, name) in enumerate(zip(sim_dict['pcs'], sim_dict['object_ids'], sim_dict['name'])):
    if pc.size == 0:
        continue
    # plot points in 3D with color based on object id in the respecitve panel
    ax = fig.add_subplot(2, 2, i+1, projection='3d')
    ax.scatter(pc[::5, 0], pc[::5, 1], pc[::5, 2], c=obj_id[::5], cmap=cmap, s=1)
    # set equal axes
    ax.set_box_aspect(box)
    # set limits and labels
    ax.set_xlim(-75, 200)
    ax.set_xlabel('X')
    ax.set_ylim(-125, 150)
    ax.set_ylabel('Y')
    ax.set_zlim(0, 100)
    ax.set_zlabel('Z')
    ax.set_title(name)

mapper = mpl.cm.ScalarMappable(norm=norm, cmap=cmap)
mapper.set_array([lower-deltac, upper+deltac])
ax2 = fig.add_axes([0.95, 0.1, 0.02, 0.8])
cbar = fig.colorbar(mapper,
             cax=ax2, orientation='vertical',
             label="Object ID", ticks=[0, 1, 2, 3])
plt.show()