Internal WGS84 definition

PatGPatG Global Mapper UserPosts: 54Trusted User
edited April 2010 in Technical Support
Mike,
I have a local 7 parameter transformation based on a GRS80 ellisoid that I am trying to use with GlobalMapper ver 11. Unfortunately when converting my test data it results in a difference to our other transformation software of 0.2m East and 1.8m North.

We believe this may be due a difference in the WGS84 epoch definition being used by each software application.

Since GM does not allow us to see the internal definitions and parameters being used for standard transformations can you provide this information to me so that we can assess the cause of these differences?

GM does not allow the editing of standard transformations but it would be a good idea to allow users access to the parameters to do their own checks. It would also be a good idea to allow users to obtain these parameters as a template for their own user defined transformations instead of having to enter all parameters manually for each new definition. This would assist with avoiding errors and typos by the user.

Your assistance would be greatly appreciated...

Comments

  • PatGPatG Global Mapper User Posts: 54Trusted User
    edited March 2010
    Mike,
    Sorry, should have added that the 7 par we have is from GRS80 to AGD66 (locally defined).
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited March 2010
    Pat,

    The datum transformation definitions are available at http://www.globalmapper.com/helpv11/datum_list.htm. Note that there is a built-in AGD66 datum in Global Mapper that uses the NTv2 conversion tables, which should be the most accurate transformation method available.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • PatGPatG Global Mapper User Posts: 54Trusted User
    edited March 2010
    Mike,
    We have defined our own ellipsoid and 7 parameters and have added these in GlobalMapper. However, when I try and load the saved *.prj file I get a parsing error and it can't load the projection. Looking in the help file it says that user defined ellipsoids and datums are saved in a "Custom_Datums.txt" file in the GM Installation folder. I can not find this file and I have to re-enter the ellipsoid and datum definition each time I start GM.

    Is this correct?

    PS. We can't use the built-in AGD66 datum because it is not correct for the location which has a modified datum definition, hence my issues here.....
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited March 2010
    Pat,

    In GM v11 the custom_datums.txt file is saved in the application data folder for Global Mapper, which is listed on the Help->About dialog. Can you check there and see if your custom_datums.txt file is there?

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • PatGPatG Global Mapper User Posts: 54Trusted User
    edited March 2010
    OK Found it in my username applications data folder for GM. Doesn't this mean that any custom datums are not made available to other users of the PC? When I start GM these custum datums don't appear in the Datum/Projection lists to select. I have to enter them each time I start GM. Shouldn't they be loaded automatically? Perhaps there is something wrong with the install?

    Can I change the location of the custom data so that all users can access them?
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited March 2010
    Pat,

    Typically each user logging into a system will have a different Application Data folder in Windows as they are in the user's data folders.

    You can however change where Global Mapper stores the data. To do this, just run 'regedit', and add a string value at 'HKEY_CURRENT_USER\Software\Global Mapper\SettingsFilePath' with the value set to the desired path for the shared data. You would need to add this value with the same location for each user. Then copy your user data files there and when you run Global Mapper again that folder should be used.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • PatGPatG Global Mapper User Posts: 54Trusted User
    edited March 2010
    Mike,
    This does not seem like a logical approach to this type of information. Typically we would want all users of the software to have the same data available to them. I would imagine this to be true for most users of GlobalMapper software and the method of changing the location is really only possible for savvy computer operators and is not recommended for all. Can I please vote to have this changed for the future?

    Can you confirm if the custom_datums.txt file is loaded by GM at startup and if so what would cause my installation to not do this?

    If it does not load it at startup, is there a way to load it so that I don't have to type in the parameters each time?
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited March 2010
    Pat,

    The problem is that there is not (that I know of) a standard place that can be written to and shared for all users on a system that follows Windows guidelines. Previously this worked fine storing in the application install folder, but with Windows Vista the guidelines prohibit writing directly to the Program Files folder and anything written there would actually be ghosted somewhere else.

    What I suppose could be done is adding a way to change the data folder via the user interface rather than requiring a registry tweak.

    The custom_datums.txt file should automatically be loaded from the application data folder when Global Mapper starts up. Do you have a custom_datums.txt file in whatever folder is marked for the application data on the Help->About dialog that isn't being read on startup? Can you post that file so that I can see if it works for me?

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • PatGPatG Global Mapper User Posts: 54Trusted User
    edited March 2010
    Mike,
    Ahh! the Microsoft usefulness factor! I'm using XP so does Vista not have an "All Users" area ?? Otherwise a user option to change location would suffice.

    Please find attached two files found in my user application GM directory pointed to by help-about. As you can see I have had several goes at getting a result. The "Custom_ellipsoids.txt" file was created when I entered my user defined ellipsoid but it has values of "Name,0.0,0.0". How does GM know what size I want the ellipsoid with this information? The data I entered was;

    Semi Major = 6378137
    Semi Minor = 6356751.79631182

    Note that when I start GM, none of these datums or ellipsoids are available to select, I have to re-enter all the data.

    Your assistance is very much appreciated...
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited March 2010
    Pat,

    I took a look and found a bug causing all custom ellipsoid parameters to be written out as 0.0, which is of course useless. I have placed a new build at http://www.globalmapper.com/global_mapper11.zip with the change for you to try. Simply download that file and extract the contents into your existing v11.xx installation folder to give it a try. If you are using the 64-bit version, there is a new build available at http://www.globalmapper.com/global_mapper11_64bit.zip .

    When I correct the custom_ellipsoids.txt file and then place both files in my Application Data folder listed on the Help->About dialog all of the custom datums become available to me.

    I will look into adding an option to allow the user to customize the settings file path and to also store that in the "current machine" vs. "current user" portion of the registry so that everyone can use it. Of course not all users have the permissions to write there, so in some cases it might go to the "current user" section instead.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited March 2010
    Pat,

    I have updated Global Mapper to add an "Edit" button on the Help->About dialog, allowing you to choose a new location for the settings file data. When you edit it, the new location is stored (if possible) in the machine part of the registry and not the user portion, so other users on the same physical computer should automatically be updated to point at the new settings file location. Of course if the user doesn't have write permissions for that part of the registry, it will just update the user part instead.

    I have placed a new build at http://www.globalmapper.com/global_mapper11.zip with the change for you to try. Simply download that file and extract the contents into your existing v11.xx installation folder to give it a try. If you are using the 64-bit version, there is a new build available at http://www.globalmapper.com/global_mapper11_64bit.zip .

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • PatGPatG Global Mapper User Posts: 54Trusted User
    edited April 2010
    Mike,
    My custom datums now appear in GM but when I use this with a local TM projection GM does not appear to read the ECW embedded georeferencing or the ERS world file.

    I have an ECW mosaic that is based on my locally determined datum (Lihir_AGD66) but with a modified TM projection. The custom datum is available in GM but when I load this ECW in GM it tells me it is WGS84 datum. It would appear that GM does not check the Custom_Datums.txt file when it tries to match the embedded georeference data. Please see the attached jpg which shows the ECW Header info on the left and GM's initial projection on load.

    A GM *.prj file was also saved along with the ECW and this did not appear to be used by GM when loading the ECW.

    Can you look into this and tell me if I am doing something wrong....
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2010
    Pat,

    Can you provide a small sample ECW file and any accompanying metadata files that use this custom datum so that I can take a look and see what is happening?

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • PatGPatG Global Mapper User Posts: 54Trusted User
    edited April 2010
    Mike,
    Please find samples attached.

    Sample_01 was created from an ECW that had embedded georeferencing and world files in the correct locally defined datum. I have included a *.prj file that shows the datum definition although GM does not recognise this when loading the original ECW. Once the image was loaded and I set the correct datum parameters in GM I exported the subset (Sample_Lihir_Grid_01) with worldfiles. When I viewed the worldfiles they did not have the correct info. The ERS datum was blank and the embedded georeferencing was also blank.

    I then used an ECW header editor to correct the embedded georeferencing and a text editor to correct the ERS file and saved them as Sample_Lihir_Grid_02.

    Again GM did not recognise my local defined datum even though it is available in the drop down list and defined in my custom datum list.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2010
    Pat,

    I just tried this with a custom datum named 'Lihir_AGD66' loaded in my GM build and your Sample_Lihir_Grid_02.ecw file automatically came in using the 'Lihir_AGD66' datum. Is the datum with the name 'Lihir_AGD66' available in your datum list on the projection dialog?

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • PatGPatG Global Mapper User Posts: 54Trusted User
    edited April 2010
    Mike,
    Yes the Lihir_AGD66 datum appears in my datum selection but it does not find it when loading the same sample 02 file. It prompts me for a Datum and the Lihir_AGD66 is available to choose then.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2010
    Pat,

    Can you provide me with your current custom_datums.txt and custom_ellipsoids.txt file (since the ellipsoid fix) so that I can test with exactly what you have and see if I can reproduce this since it works when I have added the Lihir_AGD66 datum myself.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • PatGPatG Global Mapper User Posts: 54Trusted User
    edited April 2010
    Mike,
    Sorry for delay, I have been off sick. Please find attached my custom datum files.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2010
    Pat,

    I'm not sure what I was doing differently when this worked, but it doesn't work now. This is not because of the datum, which decodes fine, but because the projection is set to "LOCAL" in both the ECW and ERS file, which is not something Global Mapper can decode, so it just produces a full projection prompt with default values.

    If you save your *01.prj file as *02.prj, then the projection from that PRJ file is used and the *02.ecw file comes in automatically with the proper datum. Perhaps that is what I had going on when it worked for me the first time.

    Alternatively, if you use a known projection text string in the ECW or ERS file, then you should get the data in without prompt.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • PatGPatG Global Mapper User Posts: 54Trusted User
    edited April 2010
    Mike,
    But does'nt the *.prj file fully define the datum and projection? The projection name is just a name which GM could pretty much ignore for custom datums surely?

    Maybe I'm a bit confused but if custom datums are allowed I would have thought GM would not need to match the projection name with anything when loading the files, just accept the datum as all the parameters are defined in the custom files...

    I believe this should be handled differently by GM. Is there any prospect of getting this changed?
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2010
    Pat,

    The datum is only part of a full coordinate system definition. You need to know the projection used and any parameters, as well as the datum used. Global Mapper can determine the datum used, but that's only a small part of the full coordinate system definition. There's nothing in the ECW or ERS file that indicates what projection the coordinates are in, so Global Mapper has to ask. It can figure out the datum part by itself, but that's not very useful in the absence of a projection as well.

    In this the PRJ file does list the full projection and datum, which is why it works fine when the PRJ file is present.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globa
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