Custom datum and Projection file

[Mohabon]

Hello,

I want to import a local datum transformation base on Molodenskii 7 parameters as follows.
Then i want to use standard Transverse Mercator as projection.

Is there any quick tool to create a PRJ file that is fully compatible with PS Pro format? Is there any template that i can use for this scope?

Thanks and regards

[Dmitry Semyonov]

Hello Mohabon,

The easiest way is to save a prj file for a similar coordinate system from PhotoScan and then edit it according to your requirements. The 7-parameter Molodensky transformation is stored in TOWGS84 section: TOWGS84[dx, dy, dz, rx, ry, rz, scale].

Please also make sure to remove authority records for PROJCS, GEOGCS and DATUM records as default transformation parameters will be loaded otherwise.

[Mohabon]

Hello Dmitry and thanks.

Can you please specify angular units and sign convention? Also scale is PPM?

Thanks and kind regards,

Moh

[SuperNewb]

I keep getting "transformation not supported" when trying to make any changes to the .prj file.

Dmitry, could you elaborate on how to remove authority records.
Thanks

[Alexey Pasumansky]

Hello Mohabon,

The three translation parameters are in meters as in the three parameter case. The rotational parameters are in seconds of arc. The scaling is apparently the scale change in parts per million.

http://proj.maptools.org/gen_parms.html

[Mohabon]

Please also make sure to remove authority records for PROJCS, GEOGCS and DATUM records as default transformation parameters will be loaded otherwise.

Hello and thanks,

Could you please specify what you mean with "remove authority records fro PROJCS etc"?
Should i remove the entire line or just change number inside? It is not clear at all.

Thanks and kind regards

[Alexey Pasumansky]

Hello Mohabon,

Remove entire tag associated with AUTORITHY word.

[Mohabon]

I apologise for my ignorance, but i dont exactly understand.

Maybe a numeric example could clean the sky!

This is standard project file for Vietnam i can save from Photoscan.

PROJCS["VN-2000 / UTM zone 48N",GEOGCS["VN-2000",DATUM["Vietnam 2000",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],TOWGS84[-192.873,-39.382,-111.202,-0.00205,-0.0005,0.00335,0.0188],AUTHORITY["EPSG","6756"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.017453292519943,AUTHORITY["EPSG","9102"]],AUTHORITY["EPSG","4756"]],PROJECTION["Transverse_Mercator",AUTHORITY["EPSG","9807"]],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",105],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AUTHORITY["EPSG","3405"]]





This is customized project file with customized 7 parameters (in glow) of Molodensky-Helmert i would like to use. (I simply changed the TOWGS84 parameters.

PROJCS["VN-2000 / UTM zone 48N",GEOGCS["VN-2000",DATUM["Vietnam 2000",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],TOWGS84[210.1472,106.1365,-106.0101,2.444739015,-1.854031022,0.048485651,12.02226514],AUTHORITY["EPSG","6756"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.017453292519943,AUTHORITY["EPSG","9102"]],AUTHORITY["EPSG","4756"]],PROJECTION["Transverse_Mercator",AUTHORITY["EPSG","9807"]],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",105],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AUTHORITY["EPSG","3405"]]


Could you please make me understand what is to be changed in order to have this file good to be imported? Actually i have tried many solution, but nothing seems to be working.

Kindest regards,

-M

[Paulo]

Mohabon,

according to your canali datum definition, I created a prj file that can be imported into PhotoScan. Note thta the 7 parameters have sign inverted as in your frinition it was specified as From WGS84 and not TOWGS84....

Attached is the file... when importing into PS, it created a user defined Coordinate system called Geographic Coordinate System,

Maybe this can help,

[Mohabon]

Mohabon,

according to your canali datum definition, I created a prj file that can be imported into PhotoScan. Note thta the 7 parameters have sign inverted as in your frinition it was specified as From WGS84 and not TOWGS84....

Attached is the file... when importing into PS, it created a user defined Coordinate system called Geographic Coordinate System,

Maybe this can help,

Lovely!

It does work perfectly.

Now i wpould like to add also a PROJECTION and things are not easy aswell. Can you also fix that syntax by any chance?

Thanks and kind regards

[Paulo]

Here is an example of PRJ file for the same datum in UTM zone 14 projection...

depending on your UTM zone, you would have to change the "central_meridian" PARAMETER in the definition...

Regards,

[Mohabon]

Thanks a lot.. I think i have got the mechanism now.

Cheers and kindest regards

[johndot]

Not sure if this lands on the same subject, but I think is kind of related. I have a prj with some custom projections...is there a way to import that into PS to be able to use it in different projects?

[Paulo]

If it is in the prj format, should be no problem...