Update after testing for Tf2 "Using Time (C++)" and "Time travel (C++…

…)" (#3583)

* Update code references to match previous tutorials. Add hint to build before executing the launch commands.

source/Tutorials/Intermediate/Tf2/Learning-About-Tf2-And-Time-Cpp.rst

@@ -38,10 +38,12 @@ Open ``turtle_tf2_listener.cpp`` and take a look at the ``lookupTransform()`` ca
 
 .. code-block:: C++
 
-   transformStamped = tf_buffer_->lookupTransform(
-      toFrameRel,
-      fromFrameRel,
-      tf2::TimePointZero);
+   try {
+       t = tf_buffer_->lookupTransform(
+          toFrameRel,
+          fromFrameRel,
+          tf2::TimePointZero);
+   } catch (const tf2::TransformException & ex) {
 
 You can see that we specified a time equal to 0 by calling ``tf2::TimePointZero``.
 
@@ -58,12 +60,13 @@ Now, change this line to get the transform at the current time, ``this->get_cloc
 .. code-block:: C++
 
    rclcpp::Time now = this->get_clock()->now();
-   transformStamped = tf_buffer_->lookupTransform(
-      toFrameRel,
-      fromFrameRel,
-      now);
+   try {
+       t = tf_buffer_->lookupTransform(
+           toFrameRel, fromFrameRel,
+           now);
+   } catch (const tf2::TransformException & ex) {
 
-Now try to run the launch file.
+Now build the package and try to run the launch file.
 
 .. code-block:: console
 
@@ -94,19 +97,21 @@ To fix this, edit your code as shown below (add the last timeout parameter):
 .. code-block:: C++
 
    rclcpp::Time now = this->get_clock()->now();
-   transformStamped = tf_buffer_->lookupTransform(
-      toFrameRel,
-      fromFrameRel,
-      now,
-      50ms);
+   try {
+       t = tf_buffer_->lookupTransform(
+           toFrameRel,
+           fromFrameRel,
+           now,
+           50ms);
+   } catch (const tf2::TransformException & ex) {
 
 The ``lookupTransform()`` can take four arguments, where the last one is an optional timeout.
 It will block for up to that duration waiting for it to timeout.
 
 3 Checking the results
 ^^^^^^^^^^^^^^^^^^^^^^
 
-You can now run the launch file.
+You can now build the package and run the launch file.
 
 .. code-block:: console
 

source/Tutorials/Intermediate/Tf2/Time-Travel-With-Tf2-Cpp.rst

@@ -39,14 +39,16 @@ Edit the ``lookupTransform()`` call in ``turtle_tf2_listener.cpp`` file to
 .. code-block:: C++
 
     rclcpp::Time when = this->get_clock()->now() - rclcpp::Duration(5, 0);
-    t = tf_buffer_->lookupTransform(
-        toFrameRel,
-        fromFrameRel,
-        when,
-        50ms);
+    try {
+        t = tf_buffer_->lookupTransform(
+            toFrameRel,
+            fromFrameRel,
+            when,
+            50ms);
+    } catch (const tf2::TransformException & ex) {
 
 Now if you run this, during the first 5 seconds, the second turtle would not know where to go because we do not yet have a 5-second history of poses of the carrot.
-But what happens after these 5 seconds? Let's just give it a try:
+But what happens after these 5 seconds? Build the package then let's just give it a try:
 
 .. code-block:: console
 
@@ -71,13 +73,15 @@ Your code now would look like this:
 
     rclcpp::Time now = this->get_clock()->now();
     rclcpp::Time when = now - rclcpp::Duration(5, 0);
-    t = tf_buffer_->lookupTransform(
-        toFrameRel,
-        now,
-        fromFrameRel,
-        when,
-        "world",
-        50ms);
+    try {
+        t = tf_buffer_->lookupTransform(
+            toFrameRel,
+            now,
+            fromFrameRel,
+            when,
+            "world",
+            50ms);
+    } catch (const tf2::TransformException & ex) {
 
 The advanced API for ``lookupTransform()`` takes six arguments:
 
@@ -101,7 +105,7 @@ And at the current time, tf2 computes the transform from the ``world`` to the ``
 Checking the results
 --------------------
 
-Let's run the simulation again, this time with the advanced time-travel API:
+Build the package then let's run the simulation again, this time with the advanced time-travel API:
 
 .. code-block:: console