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# Lab 4: Exploration
**This is a draft, wait for the lab instructions to be finished before starting**
The goal of this lab is to fill a knowledge database with information perceived in the environment. You will extend the TST executor of lab3 to listen to a semantic sensor, fill new observation in the database and generate a TST for reaching all the location of interests.
In this lab you will:
* Implement a TST Executor that listen to the semantic sensor topic and fill the database.
* Use the `tst_executor` from lab 3 to explore the environment.
* Display the results of the exploration in RViz.
* Generate a TST to drive to all the locations.
## Interfacing with the database
For this lab we will use a Postgresql database, with a wrapper called \emph{kDB} which provides ROS services for executing SQL and SPARQL queries.
For this lab, we will only use the SPARQL part.
The following command will start the database:
```bash
ros2 launch lrs_kdb start_server.launch
```
The database server is very verbose, you can generally ignore what is printed in the terminal.
You can reset the content of the database with (you need to stop the database first):
```bash
rm -rf $HOME/.lrs_kdb/stores/
```
### Inserting in the database
The following service call will insert two objects in the graph named **salientpoints**, one human (with identifier 1) at coordinates `(8,10)` and one table (with identifier 2) at coordinates `(10,12)`:
```bash
ros2 service call /husky0/kDBServerNodelet/insert_triples "
graphname: 'salientpoints'
format: 'ttl'
content: '@prefix gis: <http://www.ida.liu.se/~TDDE05/gis>
@prefix properties: <http://www.ida.liu.se/~TDDE05/properties>
<id1> a <human>;
properties:location [ gis:x 8; gis:y 10 ] .
<id2> a <table>;
properties:location [ gis:x 10; gis:y 12 ] .'"
```
This will insert two objects, the first has uuid `id1`, coordinate `(8,10)` and is a `human`. The second has uuid `id2`, coordinates `(10,12)` and class `table`.
### Querying the database
The following query can be used to retrieve all the elements in the database:
```bash
ros2 service call /husky0/kDBServerNodelet/sparql_query "graphnames: ['salientpoints']
format: 'json'
query: 'SELECT ?x ?y ?z WHERE { ?x ?y ?z }'"
```
The following query can be used to retrieve all the object with their class that are near the point of coordinate `(10, 12)`:
```bash
ros2 service call /husky0/kDBServerNodelet/sparql_query "graphnames: ['salientpoints']
format: 'json'
query: '
PREFIX gis: <http://www.ida.liu.se/~TDDE05/gis>
PREFIX properties: <http://www.ida.liu.se/~TDDE05/properties>
SELECT ?obj_id ?class ?x ?y WHERE { ?obj_id a ?class ;
properties:location [ gis:x ?x; gis:y ?y ]
FILTER( 9.9 < ?x && ?x < 10.1 && 11.9 < ?y && ?y < 12.1) .
}'"
```
You can use `ros2 service info` to get the type of the `sparql_query` service call and `ros2 interface` to access the definition of the service.
## Semantic sensor
The sensor output observations on a topic called `/semantic_sensor`. You should use `ros2 topic` and `ros2 interface` to introspect the topic, to find its type, look at the values sent, etc...
# Exploration
In [Lab 3](lab3), you have created a TST executor that move the robot to explore the environment. We will extend the functionality of lab3 and add a new type of TST Executor that can be used to record observations from `/semantic_sensor` and save them in the database.
In `lab3_node`:
* Create a new TST Executor for `record-semantic`, it takes as parameters
** `topic` the name of the topic
** `graphname` the name of the graph used to save the data
* Listen for new observations on the given topic
* Check in the graph specified with `graphname` if the observations are already inserted (using a query). For instance the following query can be used, it should return a single element (you need to replace `someid` and `someclasss` with the correct values from the message):
```sparql
PREFIX gis: <http://www.ida.liu.se/~TDDE05/gis>
PREFIX properties: <http://www.ida.liu.se/~TDDE05/properties>
SELECT ?x ?y FROM 'salientpoints' WHERE { <someid> a <someklass> ;
properties:location [ gis:x ?x; gis:y ?y ] . }
```
** Make sure to keep `<` and `>` they indicate a URI in the query, without them the query is invalid and will not be executed, so you can replace `<someid>` by `<somethingelse>` but not `somethingelse`.
** Replace `salientpoints` with the TST parameter for `graphname`.
** This query need to be executed with a service call to `/kDBServerNodelet/sparql_query`. You can check the official tutorial for [Python](https://docs.ros.org/en/galactic/Tutorials/Beginner-Client-Libraries/Writing-A-Simple-Py-Service-And-Client.html) or [C++](https://docs.ros.org/en/galactic/Tutorials/Beginner-Client-Libraries/Writing-A-Simple-Cpp-Service-And-Client.html) to learn how to make a service call.
** In the call to `/kDBServerNodelet/sparql_query`, the fields `bindings` and `service` are unused for this lab and can be set to an empty string.
* If the object has not been observed yet in the database. Add new observation using the insert triples service call (replace 'salientpoints' with the TST parameter for `graphname`).
* In C++, add `air_simple_sim_msgs` as a dependency in `CMakeLists.txt`, using `find_package` and setting the correct dependencies for your executable.