In this article, you will learn how to use GEWEL to find the date and time a photo was created, provided the location of the photo is known. Two weaknesses will be used in this example: [[GEWEL-5. Shadows of Objects]] and [[GEWEL-7. Trademark]] as well as some of their techniques ![[uog-source-1.png]] >[!abstract] >- [[UoG-2. Getting Date and Time of Creation#^eb5097|Getting input data]] >- [[UoG-2. Getting Date and Time of Creation#^6db3ec|GEWEL-5. Shadows of Objects]] > - [[UoG-2. Getting Date and Time of Creation#^f176c2|GETL-5.9. Draw the North Line]] > - [[UoG-2. Getting Date and Time of Creation#^b33de3|GETL-5.6. Select a Suitable Object with a Shadow]] > - [[UoG-2. Getting Date and Time of Creation#^e8a609|GETL-5.4. Calculate an Azimuth of the Sun]] >- [[UoG-2. Getting Date and Time of Creation#^d67ed9|GEWEL-7. Trademark]] > - [[UoG-2. Getting Date and Time of Creation#^a7af0b|GETL-7.3. Identify a Brand of an Object]] > - [[UoG-2. Getting Date and Time of Creation#^60fb5f|GETL-7.2. Get Technical Parameters of an Object]] >- [[UoG-2. Getting Date and Time of Creation#^deecb7|GEWEL-5. Shadows of Objects]] > - [[UoG-2. Getting Date and Time of Creation#^f4900c|GETL-5.7. Calculate the Length of the Shadow]] > - [[UoG-2. Getting Date and Time of Creation#^c2d845|GETL-5.5. Calculate the Ratio of the Length of the Object's Shadow to Its Height]] > - [[UoG-2. Getting Date and Time of Creation#^079ecb|GETL-5.2. Get Creation Date and Time Using Azimuth and Ratio]] >- [[UoG-2. Getting Date and Time of Creation#^7f12e4|Conclusion]] ## Getting input data ^eb5097 Once a photograph is obtained, the objects that will be used as inputs need to be selected and collected ![[uog-date-time-1.png]] ## Applying weakness: Shadows of Objects ^6db3ec The [[GEWEL-5. Shadows of Objects]] weakness allows us to extract information from the shadows of objects ![[uog-[coord-24]-[date-time-2].png]] ### GETL-5.9. Draw the North Line ^f176c2 Let's use the [[GETL-5.9. Draw the North Line]] technique to draw the north line. This means that we need to draw a straight line on this picture that points north. To do this, select the objects on the satellite image that are present in the given picture. In this case it is a lamppost and two drawings of road markings. Let's draw straight lines `1` and `2` from the lamppost to the marking drawings. Also draw a straight line from the lamppost pointing north `3` ![[uog-date-time-3.png]] Let's measure the angles between all the lines using a protractor. You can use the protractor overlay on an image by editing images or using an online service [Angle measurement](https://www.ginifab.com/feeds/angle_measurement/) ![[uog-date-time-4.png]] The angle between the lines `1` and `2`: $\beta=38°$ Between lines `2` and `3`: $\alpha=47°$ ![[uog-date-time-5.png]] Let us calculate the ratio `r` between the angles `α` and `β`: $r={\frac{\alpha}{\beta}}={\frac{47°}{38°}}\simeq 1.237$ Thus, the angle `α` is greater than the angle `β` by a factor of about 1.237. Let's go back to the photo and draw the same lines from the lamppost. Let's draw the lines `1` and `2` to the same road marking drawings. Let the angle between lines `1` and `2` be: $\beta_{1}$ ![[uog-date-time-6.png]] To draw the `3` line, we need to know the value of the angle between the `1` and `2` lines: $\beta_{1}=10.5°$ ![[uog-date-time-7.png]] From this perspective, the angles between the lines are different, but the ratio `r` between the angles remains the same, so knowing the ratio `r` and the value of the angle between `1` and `2` lines, we will find and draw the angle between `2` and `3` lines in the given picture: $\alpha_{1}=r\times \beta_{1}=1.237\times 10.5° \simeq 13°$ ![[uog-date-time-8.png]] Thus, we have drawn a line in the picture that points north ![[uog-date-time-9.png]] ### GETL-5.6. Select a Suitable Object with a Shadow ^b33de3 Let's use the [[GETL-5.6. Select a Suitable Object with a Shadow]] technique and select a suitable object to work with its shadow ![[uog-date-time-10.png]] Draw a line parallel to the line pointing north from the selected object ![[uog-date-time-11.png]] ### GETL-5.4. Calculate an Azimuth of the Sun ^e8a609 Let's use the [[GETL-5.4. Calculate an Azimuth of the Sun]] technique to calculate the azimuth, which is the angle between the line pointing north and the direction of the sun's ray. Let us draw and label the lines: `1` — the line showing the direction of the sun's ray `2` — the line perpendicular to the road `3` — the line parallel to the road. `4` — the line pointing to the north. Thus, we need to find the angle between the lines `1` and `4` ![[uog-date-time-12.png]] Let us draw the diagram, taking into account the position of the tiles. Note that the tile has a ratio of sides `1:2`, which allows us, by drawing right triangles, to find the ratio of their cathetes. We also denote the angles to be found - `α`, `β` and `γ` ![[uog-date-time-13.png]] Knowing the ratio of the cathetes of right triangles, we can use the inverse of the tangent function, the arctangent, and find the angles `α` and `β`: $\beta=\arctan\Big(\frac{1}{5}\Big)\simeq 11.31°$ $\alpha=\arctan\Big(\frac{3}{4}\Big)\simeq 36.87°$ Having obtained the value of angles `α` and `β`, we find `γ` — azimuth: $\gamma=90°+\alpha+\beta=90°+36.87°+11.31°=138.18°$ ## Applying weakness: Trademark ^d67ed9 Realizing the weakness of [[GEWEL-7. Trademark]], we turn our attention to the vehicle which parameters can be obtained based on its model ![[uog-date-time-14.png]] ### GETL-7.3. Identify a Brand of an Object ^a7af0b Using the [[GETL-7.3. Identify a Brand of an Object]] technique, we get the brand of a car. Using [Google Lens](https://lens.google/), we get the Tesla Model 3 ![[uog-date-time-15.png]] ### GETL-7.2. Get Technical Parameters of an Object ^60fb5f Using the [[GETL-7.2. Get Technical Parameters of an Object]] technique, find the height and type of tire ![[uog-date-time-16.png]] ![[uog-date-time-17.png]] Then the height of the car: $h=1443mm$ Tire width: $w=235mm$ ## Applying weakness: Shadows of Objects ^deecb7 Look at the vehicle from the point of view of weakness [[GEWEL-5. Shadows of Objects]] ### GETL-5.7. Calculate the Length of the Shadow ^f4900c Let's use the [[GETL-5.7. Calculate the Length of the Shadow]] technique to calculate the length of the vehicle's shadow. Since the shadow is approximately the same distance as the wheel, knowing the dimensions of the wheel, we can calculate the length of the shadow `l`: $l=4.18\times w = 4.18\times 235mm = 982.3mm$ ![[uog-date-time-18.png]] ### GETL-5.5. Calculate the Ratio of the Length of the Object's Shadow to Its Height ^c2d845 Let us use the technique [[GETL-5.5. Calculate the Ratio of the Length of the Object's Shadow to Its Height]] to calculate the ratio of the length of the object's shadow `l` to its height `h`: $r_{0}=\frac{l}{h}=\frac{982.3mm}{1443mm}\simeq 0.68$ ### GETL-5.2. Get Creation Date and Time Using Azimuth and Ratio ^079ecb Let's apply the [[GETL-5.2. Get Creation Date and Time Using Azimuth and Ratio]] technique and use [SunCalc](https://www.suncalc.org/) to find the date and time the photo was created. For this purpose, let's place the point of sun ray fall in the place where the photo was taken (`25.99565829616495, 119.44233660815982`), and then choose such a time and such a date in the calendar that the Azimuth and Shadow length parameters were as close as possible to the earlier found parameters. **It is important to note that it is impossible to determine the year the photo was created using this method, only the month and date.** Thus on `September 25` at `10:26 UTC+8` the values of Azimuth (`138.05°`) and Shadow length (`0.68`) were as close as possible to those found earlier: $\gamma=138.18°$ $r_{0}=0.68$ The answer is: `September 25, 10:26 UTC+8` ![[uog-date-time-19.png]] ## Conclusion ^7f12e4 So, having decomposed and structured the search process, we solved the problem in a relatively short time. Here's a list of the techniques that were used for that case: - [[GETL-5.9. Draw the North Line]] - [[GETL-5.6. Select a Suitable Object with a Shadow]] - [[GETL-5.4. Calculate an Azimuth of the Sun]] - [[GETL-7.3. Identify a Brand of an Object]] - [[GETL-7.2. Get Technical Parameters of an Object]] - [[GETL-5.7. Calculate the Length of the Shadow]] - [[GETL-5.5. Calculate the Ratio of the Length of the Object's Shadow to Its Height]] - [[GETL-5.2. Get Creation Date and Time Using Azimuth and Ratio]]