GPSers Attached to this email is a spreadsheet containing the data we obtained this past Monday.
I've gotten rid of the useless columns and merged everyone's data into a single sheet!
Also, modified some of the columns as described below.
Descriptions of the columns:
Sec - this is time in seconds from 2pm on Monday,
There are five columns for each person's data. Their names start with C, F, or P for
Cannon Green, Parking garage, or Field. This is followed by the initial of the person's
first name. So for example, Andrew was on Cannon Green and his data columns start
with CA_
Here are the five columns for Andrew's data:
CA_Lat - the north latitude in ddmm.mmmm format as recorded on Cannon Green by
Andrew's GPS/Laptop.
CA_Long - the west longitude in ddmm.mmmm format as recorded on Cannon Green by
Andrew's GPS/Laptop.
CA_N - the number of satellites on which Andrew's laptop was locked.
CA_D - the dimensionality of the fix for Andrew's laptop. (Should be 3 for a 3D fix and 2
for a 2D fix. We're not going to process altitude, so this is only important for deciding if
the GPS units are doing the same processing.)
CA_Fix - This is a number which is the sum of 1, if satellite 1 is locked on plus 2 if
satellite 2 is locked on plus 4 if satellite 3 is locked on plus 8 if satellite 4 is locked on
and so on. (A binary representation of which satellites are used for the fix.) This and the
CA_D column were generated from the $GPGSA line that immediately follows the
$GPGGA line.
The point is: two receivers are locked onto the same satellites if and only if they have the
same non-zero values in the _Fix column.
After Andrew’s data come 6 more sets of five columns:
CE_ Cannon Green, Elizabeth
CR_ Cannon Green, Rob
FD_ Field, Dominic
FP_ Field, Pete LC
PJ_ Parking Garage, Julius
PP_ Parking Garage, Pete H
The spreadsheet also includes a plot which shows, for each person's data, how many
satellites were locked on.
The table shows how many rows are in the spreadsheet where the different receivers were
locked on the same satellites:
CA
CE
CR
FD
FP
PJ
PP
CA
1821
333
289
14
67
35
33
CE
CR
FD
FP
PJ
PP
1580
670
0
733
120
95
2073
155
621
369
203
1925
137
80
75
1851
0
120
1892
1218
1816
For examples, there are 1821 entries in the spreadsheet where CA_Fix is non-zero and
1816 entries where PP_Fix is non-zero. (Look at the intersections of row CA and column
CA or row PP and column PP.) Of these, there are 33 in which CA_Fix is the same as
PP_Fix. (Look at row PP and column CA). In other words, there are 33 data points in
which Andrew’s receiver on Cannon Green andPete’s receiver on the parking garage
were locked on the same satellites.
Data Analysis Assignments:
There are 26 non-zero entries in the table above: There are 9 students. So I propose that
each of you do three sets of analysis.
Student
Andrew
Brian
Dominic
Elizabeth
Jonathan
Julius
Peter H
Peter LC
Rob
First Analysis
CA-CA
CA-CE
CA-CR
CA-FD
CA-FP
CA-PJ
CA-PP
CE-CE
CE-CR
Second Analysis
CE-FP
CE-PJ
CE-PP
CR-CR
CR-FD
CR-FP
CR-PJ
CR-PP
FD-FD
Third Analysis
FD-FP
FD-PJ
FD-PP
FP-FP
FP_PP
PJ-PJ
PJ-PP
PP-PP
CR-FP All
For example, Andrew should do CA-CA, CE-FP, and FD-FP What this means is that he
should look at the CA, CE, FP, and FD data for latitude and longitude, find the average
and remove it (that is make columns that are the 8 latitude and longitude columns with
the averages subtracted). Then convert to meters: North South meters =
6371000*Radians(latitude differences)/60; East West meters =
6371000*Cos(Radians(40))*Radians(longitude differences)/60.
For CA-CA, make a plot of the North-South differences in meters (vertical) vs the EastWest differences in meters (horizontal). Also calculate the standard deviation of the NS
and EW differences. This analysis should only include the data, where CA_Fix is nonzero (so that Andrew’s receiver was looked on to satellites).
For CE-FP, there are the NS differences for CE and for FP – these should be differenced
again (to get the error of Elizabeth’s receiver relative to the error of Pete’s receiver).
Same for the EW differences. The analysis should only use the data where CE_Fix is
non-zero and the same as FP_Fix, so both receivers are locked on to the same satellites. A
plot of the NS “double differences” vs the EW “double differences” should be produced
and also the standard deviations of the double differences should be calculated.
Whew!
All the other analyses should be done in the same way. When only one receiver is being
analyzed it should be similar to the CA-CA analysis described above. Whenever two
different receivers are being analyzed, it should be similar to the CE-FP analysis
described above. There is one exception: the analysis “CR-FP All” means to throw in all
the data provided both receivers have lock. So the analysis includes all the data where
both CE_Fix and FP_Fix are non-zero. So each receiver has lock on some satellites but
not necessarily the same ones as the other receiver.
I hope this is clear! If not, email me!
- Ed