When exporting Blue book format in ashtech solutions it produces two files one with an .bfl extension and one with a .gfl extension. I see other programs that export blue book format and produce a file with .ngs extension???

Are the formats the same?

You need 3 files for bluebooking a GPS project:

G-file: The unadjusted vector solutions.

B-file: Project information and station occupation data.

D-file: Station description file.

I don't think the file names (or extensions) are important, it's the file contents that matter. It sounds like the .GFL is your G-file, and .BFL is the B-file.

Complete specifications can be found on the NGS Bluebook Page.

You'll have to create the D-file yourself; see the NGS WDDPROC Page for appropriate software.

Thanks Jim for the help

Mr. Frame is correct, file extensions are not important. Compliance with the FGCS file format specifications *is* important.

Unfortunately, my experience with the Ashtech software revealed a number of problems with the files created. There were a number of missing elements and odd choices.

The most recent version of TGO has an excellent utility to generate these files. TGO succeeds largely by its linkage to an editor allowing users to add missing elements.

You can edit the Ashtech generated files using the NGS CR8BB program

The real test of the software is its ability to pass the testing programs and to work in the NGS ADJUST package.

BTW, in addition to the B, G and D files you must also create A-files to control the adjustment.

When you download the ADJUST package from the NGS site it includes sample B, A and G files as well as a document describing how to perform constrained adjustments the NGS way. Projects submitted to the NGS must be processed in the way described.

I created a document describing how to submit a GPS project to the NGS. You can view it here


Modified By Mike Mulcare on 12/7/2002 at 5:23 PM

Under the specs in NGSNOS 58.
What type of instruments is best for the meteorological data?
Is a basic psychrometer sufficient...
What kind of barometer is used?
Regards,
RAH

[Warning -- non-expert perspective ahead!]

I don't think it's critical in either case; I'm not even sure the met data is invoked unless the processing turns up unacceptable results.

On the first height mod project in which I was involved ('99) we used sling psychrometers and coffee-can-size barometers. On the one we did this last summer, we substituted some cheap digital therometer/hygrometer units for the sling variety. Although we still used the coffee-can barometers, I bet a less-expensive instrument would provide acceptable results.

The FBN specifications indicate that the barometer used should be accurate to 3-mbar for the barometer and 0.2 deg C for the psychrometer.

I doubt most of the instruments used meet these specifications. I also doubt that most are have been calibrated. I suspect the observations are not done as intended. See the extract below (from TM 58)

"Before taking weather observations, the meteorological instruments should be allowed ample time (approximately 10 minutes) to stabilize to ambient conditions. Observations of wet- and dry-bulb temperatures must be observed and recorded to at least the nearest 1 degree Celsius. Barometric readings must be observed and recorded to at least the nearest 1 millibar. Meteorological data should be collected at or near the antenna phase center. All equipment must be checked for proper calibration."

I believe it is clear from research (see the Rothbacher article in Vertical Reference Networks) that surface meteorological observations provide worse results that those obtained using a good model and mapping function (Saastamoinen and Neil respectively).

We have a project and the field work is referenced to the 58 memo. I have seen the sling psycometers in Forestry Suppliers, Ben Meadows and another online source for lab equipment. The barometer has me stuck. The station sites are 4 - 7 miles +/- south of an international airport...it seems that it would be reasonable to rely on their (airport) barometric readings.

If this project is intended for submission to the NGS, discuss the issue with their Project Development Branch.

The use of observations at other than the site is inconsistent with the extract from TM58 shown in the posting above. The extract even refers to the observations being taken at the height of the L1PC.