{ "id": 224491, "title": "What is the difference between the timestamp in the first and last column of WIFI data?", "url": "/competitions/indoor-location-navigation/discussion/224491", "author_name": "MAMOMIMOMU", "post_date": "2021-03-08T17:53:57.932000", "votes": 12, "comment_count": 10, "views": 0, "content": "

I watched https://youtu.be/xt3OzMC-XMU?t=690 but it says these two timestamps are different by up to 30 sec, and it's important to handle this gap.
\nBut I'm not sure of the difference between these two timestamps. The last seen timestamp is, according to the video, when the device found the wifi(I don't even know what it exactly means). Could anyone tell me where these two timestamps came from and why they are different from each other?

", "messages": [ { "id": 1231150, "postDate": "2021-03-08T17:53:57.933Z", "content": "

I watched https://youtu.be/xt3OzMC-XMU?t=690 but it says these two timestamps are different by up to 30 sec, and it's important to handle this gap.
\nBut I'm not sure of the difference between these two timestamps. The last seen timestamp is, according to the video, when the device found the wifi(I don't even know what it exactly means). Could anyone tell me where these two timestamps came from and why they are different from each other?

", "rawMarkdown": "I watched https://youtu.be/xt3OzMC-XMU?t=690 but it says these two timestamps are different by up to 30 sec, and it's important to handle this gap.\nBut I'm not sure of the difference between these two timestamps. The last seen timestamp is, according to the video, when the device found the wifi(I don't even know what it exactly means). Could anyone tell me where these two timestamps came from and why they are different from each other?", "votes": 11 }, { "id": 1236978, "postDate": "2021-03-13T15:55:22.357Z", "content": "

The meaning of last seen field is documented here :
\nhttps://developer.android.com/reference/android/net/wifi/ScanResult

\n

It says : \"timestamp in microseconds (since boot) when this result was last seen. \"

\n

I can attempt a guess :

\n\n
\n

Either the wifi access point has never been scanned => nothing is returned and nothing is in the dataset for this timestamp
\n Either the wifi access point is in range => then lastseen timestamp is updated with current time stamp and fresh values are returned
\n Either the wifi access point is not in range anymore => then lastseen timestamp is not updated, and previously seen values are returned

\n
\n

That would mean that we need to remove wifi scans which last seen timestamp is too old.
\nBut it's not obvious how to handle this removing because :

\n", "rawMarkdown": "The meaning of last seen field is documented here :\nhttps://developer.android.com/reference/android/net/wifi/ScanResult\n\nIt says : \"timestamp in microseconds (since boot) when this result was last seen. \"\n\nI can attempt a guess :\n- The first timestamp is the time when the scanning device calls the scan function.\n- When the device calls the scan function, there may be 3 possibilities for scan result values :\n> Either the wifi access point has never been scanned => nothing is returned and nothing is in the dataset for this timestamp\n> Either the wifi access point is in range => then lastseen timestamp is updated with current time stamp and fresh values are returned\n> Either the wifi access point is not in range anymore => then lastseen timestamp is not updated, and previously seen values are returned\n\nThat would mean that we need to remove wifi scans which last seen timestamp is too old. \nBut it's not obvious how to handle this removing because :\n- in the test set, timestamps of first column start at 0.\n- lastseen timestamp is a timestamp \"since boot\" : we have no guarantee that the device boot (switch on) time is the same as the first timestamp of a path.", "votes": 3, "replies": [ { "id": 1237006, "postDate": "2021-03-13T16:32:03.613Z", "content": "

I've looked at an example in the dataset: and you can have significant difference between first timestamp column and lastseen one (you can often have more than 10 seconds)

\n

So it seems this issue must actually be handled

", "rawMarkdown": "I've looked at an example in the dataset: and you can have significant difference between first timestamp column and lastseen one (you can often have more than 10 seconds)\n\nSo it seems this issue must actually be handled" }, { "id": 1237079, "postDate": "2021-03-13T18:07:42.420Z", "content": "

I've also seen in the dataset that for a given path, in many cases, the lastseen timestamp can be older than the first timestamp of the first occuring wifi access point which seems strange. Maybe that's due to some delay between scan call by the device and the scan result (which can be several seconds)

", "rawMarkdown": "I've also seen in the dataset that for a given path, in many cases, the lastseen timestamp can be older than the first timestamp of the first occuring wifi access point which seems strange. Maybe that's due to some delay between scan call by the device and the scan result (which can be several seconds)" } ] }, { "id": 1233140, "postDate": "2021-03-10T07:10:11.730Z", "content": "

Can you give us the meaning of 'last receive AP beacons frame'.
\nIt looks like this last timestamp should follow the initial timestamp,which is not the case.
\nThanks in advance

", "rawMarkdown": "Can you give us the meaning of 'last receive AP beacons frame'.\nIt looks like this last timestamp should follow the initial timestamp,which is not the case.\nThanks in advance", "replies": [ { "id": 1240655, "postDate": "2021-03-16T14:59:51.880Z", "rawMarkdown": "", "isDeleted": true } ] }, { "id": 1232896, "postDate": "2021-03-10T03:16:43.497Z", "content": "

The first timestamp is when you get the wifi_scan, which contains a ap_list.
\nThe last seen timestamp is when Android device last recieve this AP's beacon frame

", "rawMarkdown": "The first timestamp is when you get the wifi_scan, which contains a ap_list.\nThe last seen timestamp is when Android device last recieve this AP's beacon frame", "replies": [ { "id": 1236613, "postDate": "2021-03-13T09:56:41.297Z", "content": "

Thank you for your comment. So you mean first time stamp indicates the time when the smart phone enters the area accessible to the wi-fi, and last seen timestamp is almost equivalent to the time when the device is out of the area? Once the device is within the area and connected to wifi they communicate some data to each other with a timestamp, and the smart phone stores the records of these communications, which are exactly the data we now have right? I'm not sure how often they send data to each other but \"last seen\" literally means the last communication recorded in the smartphone, and it's likely to mean the last seen timestamp is almost same as the time when the device goes out of the area. Is my understanding correct?
\nThanks in advance.

", "rawMarkdown": "Thank you for your comment. So you mean first time stamp indicates the time when the smart phone enters the area accessible to the wi-fi, and last seen timestamp is almost equivalent to the time when the device is out of the area? Once the device is within the area and connected to wifi they communicate some data to each other with a timestamp, and the smart phone stores the records of these communications, which are exactly the data we now have right? I'm not sure how often they send data to each other but \"last seen\" literally means the last communication recorded in the smartphone, and it's likely to mean the last seen timestamp is almost same as the time when the device goes out of the area. Is my understanding correct? \nThanks in advance.", "votes": 1 }, { "id": 1236614, "postDate": "2021-03-13T09:58:01.130Z", "content": "

Oh and could you tell me what an ap_list is? Did I overlook sth basic?

", "rawMarkdown": "Oh and could you tell me what an ap_list is? Did I overlook sth basic?", "votes": 1 }, { "id": 1240657, "postDate": "2021-03-16T15:00:37.683Z", "content": "

WiFi is not an instant variable, so is this the reason why LSTM or RNN achieves better results?😃

", "rawMarkdown": "WiFi is not an instant variable, so is this the reason why LSTM or RNN achieves better results?😃" } ] }, { "id": 1231859, "postDate": "2021-03-09T10:09:37.490Z", "content": "

I would also like to know

", "rawMarkdown": "I would also like to know" } ], "comments": [ { "id": 1236978, "author_name": "François BOYER", "author_url": "", "post_date": "2021-03-13T15:55:22.357000", "content": "

The meaning of last seen field is documented here :
\nhttps://developer.android.com/reference/android/net/wifi/ScanResult

\n

It says : \"timestamp in microseconds (since boot) when this result was last seen. \"

\n

I can attempt a guess :

\n\n
\n

Either the wifi access point has never been scanned => nothing is returned and nothing is in the dataset for this timestamp
\n Either the wifi access point is in range => then lastseen timestamp is updated with current time stamp and fresh values are returned
\n Either the wifi access point is not in range anymore => then lastseen timestamp is not updated, and previously seen values are returned

\n
\n

That would mean that we need to remove wifi scans which last seen timestamp is too old.
\nBut it's not obvious how to handle this removing because :

\n", "votes": 3, "replies": [ { "id": 1237006, "author_name": "François BOYER", "author_url": "", "post_date": "2021-03-13T16:32:03.613000", "content": "

I've looked at an example in the dataset: and you can have significant difference between first timestamp column and lastseen one (you can often have more than 10 seconds)

\n

So it seems this issue must actually be handled

", "votes": 0, "replies": [] }, { "id": 1237079, "author_name": "François BOYER", "author_url": "", "post_date": "2021-03-13T18:07:42.420000", "content": "

I've also seen in the dataset that for a given path, in many cases, the lastseen timestamp can be older than the first timestamp of the first occuring wifi access point which seems strange. Maybe that's due to some delay between scan call by the device and the scan result (which can be several seconds)

", "votes": 0, "replies": [] } ] }, { "id": 1233140, "author_name": "Evdilos_Ikaria", "author_url": "", "post_date": "2021-03-10T07:10:11.730000", "content": "

Can you give us the meaning of 'last receive AP beacons frame'.
\nIt looks like this last timestamp should follow the initial timestamp,which is not the case.
\nThanks in advance

", "votes": 0, "replies": [ { "id": 1240655, "author_name": "", "author_url": "", "post_date": "2021-03-16T14:59:51.880000", "content": "", "votes": 0, "replies": [] } ] }, { "id": 1232896, "author_name": "WU YUEPENG", "author_url": "", "post_date": "2021-03-10T03:16:43.497000", "content": "

The first timestamp is when you get the wifi_scan, which contains a ap_list.
\nThe last seen timestamp is when Android device last recieve this AP's beacon frame

", "votes": 0, "replies": [ { "id": 1236613, "author_name": "MAMOMIMOMU", "author_url": "", "post_date": "2021-03-13T09:56:41.297000", "content": "

Thank you for your comment. So you mean first time stamp indicates the time when the smart phone enters the area accessible to the wi-fi, and last seen timestamp is almost equivalent to the time when the device is out of the area? Once the device is within the area and connected to wifi they communicate some data to each other with a timestamp, and the smart phone stores the records of these communications, which are exactly the data we now have right? I'm not sure how often they send data to each other but \"last seen\" literally means the last communication recorded in the smartphone, and it's likely to mean the last seen timestamp is almost same as the time when the device goes out of the area. Is my understanding correct?
\nThanks in advance.

", "votes": 1, "replies": [] }, { "id": 1236614, "author_name": "MAMOMIMOMU", "author_url": "", "post_date": "2021-03-13T09:58:01.130000", "content": "

Oh and could you tell me what an ap_list is? Did I overlook sth basic?

", "votes": 1, "replies": [] }, { "id": 1240657, "author_name": "Chunyu Wei", "author_url": "", "post_date": "2021-03-16T15:00:37.683000", "content": "

WiFi is not an instant variable, so is this the reason why LSTM or RNN achieves better results?😃

", "votes": 0, "replies": [] } ] }, { "id": 1231859, "author_name": "simple", "author_url": "", "post_date": "2021-03-09T10:09:37.490000", "content": "

I would also like to know

", "votes": 0, "replies": [] } ], "raw_markdown_by_id": { "1231150": "I watched https://youtu.be/xt3OzMC-XMU?t=690 but it says these two timestamps are different by up to 30 sec, and it's important to handle this gap.\nBut I'm not sure of the difference between these two timestamps. The last seen timestamp is, according to the video, when the device found the wifi(I don't even know what it exactly means). Could anyone tell me where these two timestamps came from and why they are different from each other?", "1236978": "The meaning of last seen field is documented here :\nhttps://developer.android.com/reference/android/net/wifi/ScanResult\n\nIt says : \"timestamp in microseconds (since boot) when this result was last seen. \"\n\nI can attempt a guess :\n- The first timestamp is the time when the scanning device calls the scan function.\n- When the device calls the scan function, there may be 3 possibilities for scan result values :\n> Either the wifi access point has never been scanned => nothing is returned and nothing is in the dataset for this timestamp\n> Either the wifi access point is in range => then lastseen timestamp is updated with current time stamp and fresh values are returned\n> Either the wifi access point is not in range anymore => then lastseen timestamp is not updated, and previously seen values are returned\n\nThat would mean that we need to remove wifi scans which last seen timestamp is too old. \nBut it's not obvious how to handle this removing because :\n- in the test set, timestamps of first column start at 0.\n- lastseen timestamp is a timestamp \"since boot\" : we have no guarantee that the device boot (switch on) time is the same as the first timestamp of a path.", "1233140": "Can you give us the meaning of 'last receive AP beacons frame'.\nIt looks like this last timestamp should follow the initial timestamp,which is not the case.\nThanks in advance", "1232896": "The first timestamp is when you get the wifi_scan, which contains a ap_list.\nThe last seen timestamp is when Android device last recieve this AP's beacon frame", "1231859": "I would also like to know" } }