The integration of inside the database also opens the door to the automation of real-time analysis performed routinely on massive sets of data. For instance, this gapless framework could be used to set up early warning systems that detect behaviours of the animals that can be potentially dangerous or of particular importance for researchers. In this chapter, you will be introduced to the use of Pl/R in the context of PostGIS. You will start by exercises involving simple calculations in (logarithms, median and quantiles) to understand how Pl/R works. More elaborated exercises designed to compute the daylight times of a given location at a given date or to compute complex home range methods will then give you a basic overview of the potential of Pl/R for the study of Personal GPS Tracking Device locations.
You have exclusively worked with Small GPS Tracking Device position data. We showed how to organise these data in databases, how to link them to environmental data and how to connect them to R for further analysis. In this chapter, we introduce an example of data recorded by another type of sensor: acceleration data, which can be measured by many tags where they are associated with the GPS sensors and are widely used to interpret the behaviour of tagged cars. The general structure of these data and an overview of possibilities for analysis are given. In the exercise for this chapter, you will learn how to integrate an acceleration data set into the database created in the previous chapters and link it with other information from the database. At the end, the database is extended with acceleration data and with an automated procedure to intersect these layers with GPS positions.
you learned how to correlate Personal Tracker positions with other spatiotemporal information such as NDVI values and DEMs. However, many kinds of bio-logging sensors are available to record a large set of information related to cars. In fact, we are quickly moving from cars monitored by one single sensor, usually a GPS receiver, to cars monitored by multiple, integrated sensors that register spatial (i.e. GPS positions) and non-spatial measurements such as acceleration, temperature or GSM signal quality. In recent years, commercial solutions have emerged to deploy a camera on cars, or even internal sensors in the cars’ body to register heartbeat and body temperature. These sensors are usually integrated on a unique physical support (the collar or tag). Data from all these different sensors can be related to the spatial position of the car and to each other on the basis of the acquisition time of the recorded information, thus giving a complete picture of the car at a certain time. This integrated set of information can be used to fully decipher the cars’ behaviour in space and time. The opportunity to answer new biological questions through the information derived from these multi-sensor monitoring platforms implies a number of further challenges in terms of data management. To be able to explore the multifaceted aspects of cars’ behaviour, researchers must deal with even bigger and more diverse sets of data that require a more complex database data model and data acquisition procedures.
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Can the dash cam continue to work after the car has stalled?
for this trajectory, there is significant clustering of the missing fixes (you can test yourself whether this is also the case for the other cars). Thus, when you have one missing location, it is more likely that the next location will be missing too. Such temporal dependence in the probability to obtain fixes is not surprising, because the conditions affecting this probability are likely temporally autocorrelated. For instance, it is known that for a Rear View Mirror With Camera receiver, it is more difficult to contact the satellites within dense forests, and so when an car is in such a forest at time t, it is more likely to be still in this forest at time t +1 than at time t +2, thus causing temporal dependence in the fix-acquisition probability. Unfortunately, as said, this temporal dependence in the ‘missingness’ of locations holds the risk of introducing biases in the results of your analysis.
the Pl/R extension, a very powerful alternative to integrate the features offered by R in the database in a gapless workflow. Pl/R is a loadable procedural language that allows the use of the R engine and libraries directly inside the database, thus embedding R scripts into SQL statements and database functions and triggers. Among many advantages, Pl/R avoids unnecessary data replication, allows the use of a single SQL interface for complex scripts involving R queries and offers a tight integration of data analysis and management processes into the database. In this chapter, you will have a basic overview of the potential of Pl/R for the study of Android Rear View Camera locations. You will be introduced to the use of Pl/R, starting with exercises involving simple calculations in R (logarithms, median and quantiles), followed by more elaborated exercises designed to compute the daylight times of a given location at a given date, or to compute complex home range methods.
you discovered the Rear Mirror Camera importance of a tight integration of management and analysis tools for a proper handling of wildlife tracking data. you have seen how R can be connected to the database as a client application to perform advanced analysis algorithms and complex data processing steps. There is a very powerful alternative to integrate the features offered by R and by PostgreSQL/PostGIS in a unique workflow, one that dissolves the boundaries between management and analysis as required by the processing of data from the new generation of wildlife tracking sensors.
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The class-function shows us that Personal GPS Tracking Devices ltraj is an object from the class ltraj and list. Each element of an ltraj-object is a data. frame with the trajectory information for each burst of each car. A burst is a more or less intense monitoring of the car followed by a gap in the data. For instance, cars that are only tracked during the day and not during the night will have for each day period a burst of data. used for the GPS tracking of the roe deer in your database did not contain any intentional gaps; we therefore consider all data from an car as belonging to a single burst.
Before you dive into the analysis to Personal GPS answer your question, it is crucial to perform a preliminary inspection of the data to verify data properties and ensure the quality of your data. Several of the following functionalities that are implemented in R can also easily (and more quickly) be implemented into the database itself. The main strength of R, however, lies in its visualisation capabilities. The visualisation of different aspects of the data is one of the major tasks during an exploratory analysis. The basic trajectory format in adehabitat is ltraj, which is a list used to store trajectories from different cars. Indeed, now you see that the trajectories do contain a fair number of missing locations. If locations are missing randomly, it will not bias the results of an analysis. However, when missing values occur in runs, this may affect your results. In adehabitat, there are two figures to inspect patterns in the missing data. The function plotNAltraj shows for a trajectory where the missing values occur and can be very instructive to show important gaps in the data.
You see that there are no longer observations that deviate from the 4-hour schedule we programmed in our Portable GPS Tracker sensors, i.e. all time lags between consecutive locations are a multiple of four. You still see gaps in the data, i.e. some gaps are larger than 4 h. Thus, there are missing values. The summary did not show the presence of missing data in the trajectory; you therefore have to specify the occurrence of missing locations. The setNA function allows us to place the missing values into the trajectory at places where the GPS was expected to obtain a fix but failed to do so. You have to indicate a GPS schedule, which is in your case 4 h.
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Wireless Security Cameras several groups of computer security specialists have discovered security problems that let malicious users compromise the security of WLANs. These include passive attacks to decrypt traffic based on statistical analysis, active attacks to inject new traffic fi-om unauthorized mobile stations (based on known plain text), active attacks to decrypt traffic (based on tricking the access point), and dictionary-building attacks. The dictionary building attack is possible after analyzing enough traffic on a busy network. Security problems with WEP include, first of all, the use of static WEP keys—^many users in a wireless network potentially sharing the identical key for long periods of time, is a well-known security vubierability. This is in part due to the lack of any key management provisions in the WEP protocol. If a computer such as a laptop were to be lost or stolen, the key could become compromised along with all the other computers sharing that key.
Moreover, if Home Security Cameras every station uses the same key, a large amount of traffic may be rapidly available to an eavesdropper for analytic attacks, such as the second and third security problems with WEP, which are discussed next. Second,is a 24-bit field sent in the clear text portion of a message. This 24-bit string, used to initialize the key stream generated by the RC4 algorithm, is a relatively small field when used for cryptographic purposes. Reuse of the same IV produces identical key streams for the protection of data, and the short IV guarantees that they will repeat after a relatively short time in a busy network. Moreover, the 802.11 standard does not specify how the IVs are set or changed, and individual wireless NICs fi”om the same vendor may all generate the same IV sequences, or some wireless NICs may possibly use a constant IV. As a result, hackers can record network traffic, determine the key stream, and use it to decrypt the cipher-text.
Combined with a weakness in the RC4 key schedule, leads to a successful analytic attack, that recovers the key, after intercepting and analyzing only a relatively small amount of traffic. This attack is publicly available as an attack script and open source code. Finally, WEP provides no cryptographic integrity protection. However, the 802.11 MAC protocol uses a noncryptographic Cyclic Redundancy Check (CRC) to check the integrity of packets, and acknowledges packets with the correct checksum. The combination of noncryptographic checksums with stream ciphers is dangerous and often introduces vulnerabilities, as is in the case for WEP. There is an active attack that permits the attacker to decrypt any packet by systematically modifying the packet and CRC sending it to the AP and noting whether the packet is acknowledged. These kinds of attacks are often subtle, and it is now considered risky to design encryption protocols that do not include cryptographic integrity protection. But the JIMI Wireless Security Camera System are different,IF you want understand more, information at http://www.jimilab.com/
A window function4 performs a calculation across a set of rows that are somehow related to the current row. This is similar to an aggregate function, but unlike regular aggregate functions, window functions do not group rows into a single output row, hence they are still able to access more than just the current row of the query result. In particular, it enables you to access previous and next rows (according to a user-defined ordering criteria) while calculating values for the current row. This is very useful, as a tracking data set has a predetermined temporal order, where many properties (e.g. geometric parameters of the trajectory, such as turning angle and speed) involve a sequence of Personal Tracking Device positions. It is important to remember that the order of records in a database is irrelevant. The ordering criteria must be set in the query that retrieves data.
The result returns the list of IDs of all the Personal Tracking Devices positions that match the defined conditions. The same record detected in the previous query is returned. These examples can be used as templates to create other filtering procedures based on the temporal sequence of GPS positions and the users’ defined movement constraints. It is important to remember that this kind of method is based on the analysis of the sequence of GPS positions, and therefore results might change when new GPS positions are uploaded. Moreover, it is not possible to run them in real time because the calculation requires a subsequent GPS position. The result is that they have to be run in a specific procedure unlinked with the (near) real-time import procedure. You can test the results by reloading the GPS positions into gps_data_cars (for example, modifying the gps_sensors_cars table). If you do so, do not forget to rerun the tool to detect GPS positions in water, impossible spikes, and duplicated acquisition time, as they are not integrated in the automated upload procedure.
Although some very specific algorithms (e.g. kernel home range) must be run in a dedicated GIS or spatial statistics environment , a number of analyses can be implemented directly in PostgreSQL/PostGIS. This is possible due to the large set of existing spatial functions offered by PostGIS and to the powerful but still simple possibility of combining and customising these tools with procedural languages for applications specific to wildlife tracking. What makes the use of databases to process tracking data very attractive is that databases are specifically designed to perform a massive number of simple operations on large data sets. In the recent past, biologists typically undertook movement ecology studies in a ‘data poor, theory rich’ environment, but in recent years this has changed as a result of advances in data collection techniques. In fact, in the case of Personal GPS Homing Device data, for which the sampling interval is usually frequent enough to provide quite a complete picture of the animal movement, the problem is not to derive new information using complex algorithms run on limited data sets (as for VHF or Argos Doppler data), but on the contrary to synthesise the huge amount of information embedded in existing data in a reduced set of parameters.
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