We analyze the gravitational waveforms from our numerical relativity simulations and compare them with the simulation done at LIGO. If the length of the interferometer arms is $L$, the strain $\frac{\delta L(t)}{L}$ on the arms due to the gravitational waveform is given by $$h \equiv \frac{\delta L(t)}{L}=F_{+}(\theta,\phi,\psi)h_{+}(t;\theta_{GW},\phi_{GW})+ F_{\times}(\theta,\phi,\psi)h_{\times}(t;\theta_{GW},\phi_{GW}),$$ where $F_{+}$ and $F_{\times}$ are antenna pattern functions determined by the orientation of the LIGO detectors with respect to the binary (see Fig. 1): $$F_{+}(\theta,\phi,\psi)=\frac{1}{2}(1+\cos^{2}\theta)\cos2\phi\cos2\psi \cos\theta\sin2\phi\sin2\psi,$$ $$F_{\times}(\theta,\phi,\psi)=\frac{1}{2}(1+\cos^2\theta)\cos2\phi\sin2\psi +\cos\theta\sin2\phi\cos2\psi.$$
Fig. 1: The relative orientation of the sky and detector frames (left panel) and the effect of a rotation by the angle $\psi$ in the sky frame (right panel). (Reference: https://link.springer.com/article/10.12942/lrr20092)
Here, $\theta_{GW}$ and $\phi_{GW}$ are the spherical coordinates of the observer from the binary's frame, taking the angular momentum of the binary to point along the zaxis. These values are tabulated below.
Angle  Value  LIGO Ref 

$\theta_{GW}$  $\pi/6$  https://dcc.ligo.org/public/0122/P1500218/01 2/GW150914_parameter_estimation_v13.pdf 
$\phi_{GW}$  0  Arbitrary 
To obtain $\theta$, $\phi$, and $\psi$ for calculating $F_{+}$ and $F_{\times}$, we need the find the orientation of the binary with respect to the observers. LIGO found that on September 14 2015, 09:50:45.39 UTC, the source position was consistent with: $$ \begin{align} \text{RA} &= 8\text{h} \\ \text{DEC} &= 70^{\circ} \end{align} $$
LIGO Ref: https://dcc.ligo.org/public/0122/P1500218/012/GW150914_parameter_estimation_v13.pdfThe location sites of the observatories are given and listed below.
Detector  Latitude  Longitude  XArm Azimuth 

LIGO Hanford  46°27'19"N  119°24'28"W  N 36°W 
LIGO Livingston  30°33'46"N  90°46'27"W  W 18°S 
LIGO Ref: http://www.ligo.org/scientists/GW100916/GW100916geometry.html
Using these values, we then calculate $\theta$ and $\phi$, and setting $\psi=0$.
Detector  Angle  Value (rad) 
Ref  

LIGO Hanford 




LIGO Livingston 



Liu code can be found here
From this, we get $$ F_{+} = 0.7339 \\ F_{\times} = 0.1754 $$ Our simulation calculates $h_{+}^{NR}$ and $h_{\times}^{NR}$ at an extraction radius of $r_{ext}=4924.5M_{\odot}=7272\text{km}$. The luminosity distance between the source and LIGO has been observed to be $D_{L} = 410 \text{Mpc} = 1.265\times 10^{22} \text{km}$. Thus, we must scale our data to obtain the measured strain by LIGO: $$ h_{+} = \frac{r_{ext}}{D_{L}}h_{+}^{NR} = 5.7483\times 10^{19} h_{+}^{NR}\\ h_{\times} = \frac{r_{ext}}{D_{L}}h_{\times}^{NR} = 5.7483\times 10^{19} h_{\times}^{NR}\\ $$ The final equation for measuring the strain from our numerical simulation is then $$h \equiv \frac{\delta L(t)}{L} = 5.7483\times 10^{19}\left(0.7339\, h_{+}^{NR}(t;\pi/6, 0) +0.1754 \, h_{\times}^{NR}(t;\pi/6, 0)\right) $$