TLS-bridged co-prediction of tree-level multifarious stem structure variables from worldview-2 panchromatic imagery: a case study of the boreal forest

Figures & data

Figure 1. Location of the Seurasaari Island for test and snapshots of (a) the WPI covering the island and (b) the TLS-collected point clouds at the centre of the island.

Table 1. Statistical characteristics of the individual sample trees selected for the test.

	Min.	Max.	Mean
DBH (mm)	130	753	396
FLBH (m)	0.088	24.32	8.73
SS (°)	0.055	0.24	0.096
TH (m)	9.12	29.71	21.28
FLBH/TH	0.011	0.86	0.42

Figure 2. Schematic diagram of defining the proposed SSVs: DBH, FLBH, SS and TH (the two dotted lines are parallel).

Table 2. Definitions of the proposed texture-kind feature parameters based on WPIs.

Feature parameter	Formula
SDGL average grey level (AV)
SDGL standard derivation (SD)
SDGL smoothness (SM)
SDGL third moment (TM)
SDGL uniformity (UN)
SDGL entropy (ET)
GLCM energy (EN)
GLCM contrast (CT)
GLCM correlation (CR)
GLCM homogeneity (HO)

Figure 3. Scatterplots of the TLS-derived and manually measured DBH values for the 62 sample trees for the test.

Figure 4. Boxplots of the WPI-derived feature parameters: (a) area of crown, (b) ED and (c) the ratio between the area of crown and the area of MBR.

Figure 5. Boxplots of the WPI-derived SDGL-typed feature parameters: (a) AV, (b) SD, (c) SM, (d) TM, (e) UN and (f) ET.

Table 3. The R² values of the correlations between the TLS-derived SSVs and the Model1-based estimates for all of the specimens of the four tree species.

	DBH	SS	FLBH	TH	FLBH/TH
CA	0.056	0.060	0.143	0.058	0.031
ED	0.069	0.072	0.150	0.028	0.017
RA	0.033	0.010	0.002	0.001	0.011
AV	0.017	0.024	0.035	0.067	0.005
SD	0.044	0.003	0.020	0.010	0.001
SM	0.044	0.003	0.007	0.042	0.001
TM	0.019	0.026	0.010	0.040	0.001
UN	0.003	0.057	0.051	0.005	0.048
ET	0.001	0.042	0.005	0.001	0.045
EN	0.001	0.028	0.040	0.001	0.029
CT	0.051	0.028	0.110	0.003	0.059
CR	0.075	0.029	0.060	0.001	0.039
HO	0.044	0.062	0.070	0.001	0.180

Table 4. The R² values of the correlations between the TLS-derived SSVs and the Model2-based estimates for all of the specimens of the four tree species.

	The chosen WPI-derived feature parameters in the R^2-descending order						R^2
DBH	CR	ED	CB	CT	SD	SM	0.137
SS	ED	HO	CB	UN	ET	CR	0.119
FLBH	ED	CB	CT	HO	CR	UN	0.204
TH	AV	CB	SM	TM	ED	SD	0.312
FLBH/TH	HO	CT	TM	UN	ET	CR	0.192

Table 5. The R² values of the correlations between the TLS-derived SSVs and the Model1-based estimates for the specimens of the P. abies tree species.

	DBH	SS	FLBH	TH	FLBH/TH
CA	0.015	0.063	0.001	0.025	0.001
ED	0.032	0.062	0.001	0.022	0.001
RA	0.001	0.004	0.002	0.130	0.002
AV	0.007	0.006	0.110	0.173	0.110
SD	0.329	0.102	0.108	0.053	0.108
SM	0.329	0.103	0.105	0.048	0.105
TM	0.040	0.016	0.193	0.142	0.193
UN	0.001	0.130	0.045	0.057	0.045
ET	0.016	0.184	0.024	0.101	0.024
EN	0.001	0.097	0.062	0.009	0.062
CT	0.001	0.003	0.001	0.002	0.001
CR	0.032	0.022	0.007	0.037	0.007
HO	0.025	0.034	0.004	0.005	0.004

Table 6. The R² values of the correlations between the TLS-derived SSVs and the Model1-based estimates for the specimens of the P. sylvestris tree species.

	DBH	SS	FLBH	TH	FLBH/TH
CA	0.031	0.006	0.057	0.290	0.440
ED	0.095	0.002	0.115	0.244	0.443
RA	0.371	0.004	0.369	0.074	0.001
AV	0.001	0.001	0.060	0.103	0.032
SD	0.384	0.032	0.572	0.046	0.022
SM	0.391	0.037	0.574	0.045	0.023
TM	0.093	0.001	0.001	0.113	0.085
UN	0.283	0.122	0.208	0.130	0.290
ET	0.167	0.210	0.092	0.100	0.191
EN	0.096	0.012	0.058	0.075	0.137
CT	0.264	0.016	0.073	0.015	0.066
CR	0.410	0.014	0.229	0.001	0.068
HO	0.301	0.054	0.118	0.129	0.261

Table 7. The R² values of the correlations between the TLS-derived SSVs and the Model1-based estimates for the specimens of the P. tremul tree species.

	DBH	SS	FLBH	TH	FLBH/TH
CA	0.001	0.012	0.035	0.046	0.057
ED	0.001	0.016	0.033	0.045	0.055
RA	0.022	0.028	0.001	0.153	0.153
AV	0.049	0.080	0.001	0.096	0.096
SD	0.001	0.001	0.053	0.111	0.178
SM	0.001	0.001	0.054	0.113	0.182
TM	0.056	0.080	0.001	0.049	0.048
UN	0.034	0.046	0.022	0.085	0.059
ET	0.038	0.027	0.032	0.051	0.053
EN	0.037	0.032	0.025	0.150	0.028
CT	0.001	0.001	0.001	0.036	0.140
CR	0.001	0.002	0.003	0.044	0.022
HO	0.004	0.036	0.001	0.005	0.036

Table 8. The R² values of the correlations between the TLS-derived SSVs and the Model1-based estimates for the specimens of the Q. robur tree species.

	DBH	SS	FLBH	TH	FLBH/TH
CA	0.005	0.082	0.326	0.079	0.210
ED	0.006	0.114	0.263	0.040	0.147
RA	0.182	0.011	0.579	0.126	0.256
AV	0.324	0.001	0.332	0.041	0.054
SD	0.002	0.205	0.020	0.045	0.092
SM	0.002	0.201	0.095	0.044	0.092
TM	0.436	0.002	0.097	0.036	0.054
UN	0.126	0.083	0.395	0.003	0.031
ET	0.078	0.121	0.001	0.007	0.049
EN	0.027	0.134	0.005	0.001	0.005
CT	0.113	0.100	0.014	0.026	0.007
CR	0.078	0.002	0.066	0.059	0.045
HO	0.001	0.013	0.005	0.004	0.008

Table 9. The R² values of the correlations between the TLS-derived SSVs and the Model2-based estimates for the specimens of the P. abies tree species.

	The chosen WPI-derived feature parameters in the R^2-descending order						R^2
DBH	SD	SM	TM	ED	CR	HO	0.769
SS	ET	UN	SM	SD	EN	CB	0.698
FLBH	TM	AV	SD	SM	EN	UN	0.273
TH	AV	TM	RA	ET	SD	CR	0.504
FLBH/TH	TM	AV	SD	SM	EN	UN	0.252

Table 10. The R² values of the correlations between the TLS-derived SSVs and the Model2-based estimates for the specimens of the P. sylvestris tree species.

	The chosen WPI-derived feature parameters in the R^2-descending order						R^2
DBH	CR	SM	SD	RA	HO	UN	0.971
SS	ET	UN	HO	SM	SD	CT	0.381
FLBH	SM	SD	RA	CR	UN	HO	0.653
TH	CB	ED	UN	HO	TM	AV	0.482
FLBH/TH	CB	ED	UN	HO	ET	EN	0.252

Table 11. The R² Values of the correlations between the TLS-derived SSVs and the Model2-based estimates for the specimens of the P. tremul tree species.

	The chosen WPI-derived feature parameters in the R^2-descending order						R^2
DBH	TM	AV	ET	EN	UN	RA	0 . 074
SS	AV	TM	UN	EN	RA	ET	0.139
FLBH	SM	SD	RA	ED	ET	EN	0.347
TH	RA	EN	SM	SD	AV	UN	0.205
FLBH/TH	SM	SD	RA	CT	CB	ED	0.367

Table 12. The R² values of the correlations between the TLS-derived SSVs and the Model2-based estimates for the Q. robur species.

	The chosen WPI-derived feature parameters in the R^2-descending order						R^2
DBH	TM	AV	RA	UN	CT	CR	0.569
SS	SD	SM	EN	ET	ED	UN	0.393
FLBH	RA	UN	AV	CA	ED	TM	0.595
TH	RA	CB	CR	SD	SM	AV	0.810
FLBH/TH	RA	CB	ED	SD	SM	ET	0.675

Figure 6. Boxplots of the performance indices shown in different cases.