WelcomeMonday, January 30th, 2023
Converting .gsb (binary file) to .ggf (GEOID Models) for Trimble Access
There is a geoid model in its early stages that's been released in .gsb format by the national authority. It is released as a binary file. I wanted to do some testing to check its behavior agaisnt current geoid model and some other projects where I've got good level data.
I tried bringing it in the TSC7 however, it recognized it as invalid geoid model.
My understanding is Trimble Access only takes in .ggf file. I tried Trimble Grid Factory. But it does not have the Reference Ellipsoid I was after. I believe it was slightly changed version of GRS80 that was done in 2020.
Do you happen to have some experience in .gsb to .ggf conversion process?
Any appreciate any guidance in the matter.
If I remember correctly Grid Factory will ingest BIN files without a problem as long as you set up the import stlyle correctly.
As far as the ellipsoid goes, if your reference system uses GRS80, that's the one you want. You just have to be sure to pair the correct geoid with the coordinate system and reference control in the field.
For instance, I could load GEOID09 if I were working in NAD83(2007), or I could load GEOID12A, GEOID12B or GEOID18 for NAD83(2011). All those geoids use the GRS80 ellipsoid.
For that matter, you could use the WGS84 as a stand in for GRS80. The difference between them is unnoticeable especially for geoid separations.
Going from memory and dont have access at the moment to my saved format description documents, but the GSB (Grid Shift Binary) files were designed for grid shift values, although I seem to remember a description that showed how the format could be used for geoid separation values also, and I believe Australia? published geoid files in that format.
I have written converters for other binary geoid files in the past, BYN, BIN and one or two others.
I don't recall having a document describing the GGF file format, does such a document exist somewhere? Likely someone has reverse engineered it by now if it is not public.
Once the format of both the source and target files is known, then writing the converter itself is relatively straightforward for a programmer. There is a header portion always describing the extents, order and and type of data, then the data itself in sequential order as identified in the header.
If you locate the format descriptions for GSB and GGF files, then getting a custom converter written is one option. Otherwise contact a commercial software provider that has other converters and request the conversion of the formats you want. They likely would already have the necessary information to add the support. I am thinking of Hydromagic as one such provider
@rover83 yea true. It didn't have the datum I was after so I ended up contacting our local providers who had provided another geoid model 2 years ago. thanks for your response!
@jacob-wall your are spot on! it is for Australia. I ended up contacting our local providers if they can help me in this since we had an updated national geoid model in 2020 as well. It seems like it was provided in GSB format as well in their website so I'm hoping it is quite straight forward.
I've got no programming skills so might have to rely on other fellows for the task.
Thanks for your resposne!
You can obtain this 2020 geoid in ASCII format and Trimble Grid Factory can read and convert it to GGF, the condition is, you need to define import template the right way what is not as easy as should be. When done wrong, TGF just throws an error without any hint what is wrong. So it will be trial and error procedure. Geoid file for Australia is also huge and I can't guarantee that Trimble Grid Factory will handle it.
Here may be helpful reference
@jimcox Ohh I use those two on a normal basis Jim. Geoscience Australia (GA) is working on a quasi geoid model which intruiged me a bit and wanted to test it out. There will be various iterations to it in future as the gravity model gets updated. However, even in its infancy, I wanted to test it out on site.
They have a tool to convert it to the new 'datum' to convert it from lat long ellipsoidal height which is what I ended up using.