| Question |
Answer |
| |
|
| Are there any texts or
reference books that you would recommend to go with the lecture notes
for Satellite Positioning and Geodesy? |
Although there are many excellent GPS texts
and web pages available, there is no one ideal text that covers the
syllabus for the entire subject. If you want to see some books that
I suggest as useful, there is a list in the front of the class notes.
If you haven't got a hard copy of the notes from the Book Room, you
can access a digital version from the subject web-page. |
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|
| QUESTIONS
ABOUT ASSIGNMENT 1 |
Getting
familiar with coordinates
 |
| What format should be
used in writing-up Assignment 1? |
This prac requires a series of calculations involving
geodetic coordinates to be carried out. Present your results and any
pertinent comments that may help to explain what has been done and
what conclusions could or should be drawn. There is no need to explicitly
follow a scientific report format. By the same token, a page of coordinates,
without explanatory comments, is not acceptable. |
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|
| QUESTIONS
ABOUT ASSIGNMENT 2 |
Applications
of GPS
|
| No questions asked as
yet! |
|
| |
|
| QUESTIONS
ABOUT ASSIGNMENT 3 |
GPS navigation solution
|
| What value
should we use for the initial receiver clock error in Assignment
3 ? |
In fact, you can use any value you like. The further
away your initial value is from the true value, the longer it will
take for the solution to converge. My advice is to use an initial
value of 0 seconds. This is because we know the clock error will be
small (some milliseconds). By choosing zero as the initial value,
convergence should occur quickly. |
| In calculating the PDOP
and GDOP for Assignment 3, do we have to transform
the variance matrix from the geocentric cartesian frame into the local
(east, north up) reference frame? |
No you don't. Both PDOP and GDOP
involve all three components of position. Thus if you add the three
variances expressed in terms of geocentric cartesian coordinates or
the local system, you will get the same answer. For example:
 |
| For Assignment
3, what is an acceptable level for the PDOP and GDOP values? |
There is no definitively correct answer to this
question. DOP values of less than 5 are generally acceptable. Certainly
PDOP or GDOP values greater than 8 are cause for concern. |
| |
|
| QUESTIONS
ABOUT ASSIGNMENT 4 |
The
future of GNSS
|
| No questions asked as
yet! |
|
| |
|
| QUESTIONS
ABOUT ASSIGNMENT 5 |
GPS
control survey
|
| For Assignment
5, what datum should be used when adjusting the GPS network
in DNA? |
The project specification requires GDA94 coordinates
to be supplied for BULL, TRACK and LAWN. The easiest way to achieve
this is to adjust the network within the GDA94 reference frame.
|
| For Assignment
5, what process should be used for scaling the variance matrix
and why is this done? |
Scaling the variance matrix is done when you
are convinced that the a priori stochastic model is inappropriate
- nearly always the case with GPS observations. The sequence to
follow is :
- Perform the minimum constraint adjustment
- Eliminate any poor quality baselines (think about how you will
test this??)
- If Chi-squared is too big (again a statistical test) after bad
baselines are removed, you must conclude that the a priori
variances are too small, therefore you can legitimately scale
the variance matrix by sigma zero^2
- Re-run the adjustment
- The Chi-squared value will equal the degrees of freedom (as
expected) and sigma zero will = 1
- Only do this for the minimum constraint adjustment, not the
constrained adjustment (why??)
|
General
questions
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