topic Re: Georeferencing points misplaced after import from Link Table in ArcMap Questions

Georeferencing points misplaced after import from Link Table

GeorgHohberg — Mon, 25 May 2020 10:03:21 GMT

I am using ArcGIS 10.3. A collegue in Asia georefferenced a .tif image for me using the ArcGIS georeferencing tool. He uses the same version of ArcGIS. Before rectifying he saved the link table. He send both, the link table and the georefferenced image. Trying to adjust some of the georeferencing, I opened the original image and imported the link table. After having imported the link table, the source points are about 2 km west and 2 km north of what they should be. I cannot figure out, why. My collegue and me both use the same coordinate system (WKID 32642, WGS_1984_UTM_zone42M). Does anybody know what could be the problem?

Thanks,

Georg

Re: Georeferencing points misplaced after import from Link Table

DanPatterson — Mon, 25 May 2020 21:13:58 GMT

not a feet vs meters thing is it?

Re: Georeferencing points misplaced after import from Link Table

GeorgHohberg — Tue, 26 May 2020 05:05:33 GMT

Hey Dan,

as far as I know map units are determined by the coordinate system selected so I would not be able to change these. Changing the display units obviously does not help or do you have something else in mind regarding the units?

Re: Georeferencing points misplaced after import from Link Table

DanPatterson — Tue, 26 May 2020 13:23:36 GMT

The link table may have been made in the coordinate system of the map and not the data, hence, they could be different. Worth a check on the values of the link table and how the coordinates are defined and whether they are correct

Re: Georeferencing points misplaced after import from Link Table

GeorgHohberg — Wed, 27 May 2020 07:49:30 GMT

Hey Dan,

thanks for your efford. I checked the .prj of the Link table and the data frame properties. Both are identical.

Data frame property	.prj of Link Table
WGS_1984_UTM_zone_42N	PROJCS["WGS_1984_UTM_zone_42N"
WKID: 32642 Authority: EPSG	AUTHORITY["EPSG",32642]]
Projection: Transverse_Mercator	PROJECTION["Transverse_Mercator"]
false_easting: 500000,0	PARAMETER["false_easting",500000.0]
false_northing: 0,0	PARAMETER["false_northing",0.0]
central_meridian: 69,0	PARAMETER["central_meridian",69.0]
scale_factor: 0,9996	PARAMETER["scale_factor",0.9996]
latitude_of_origin: 0,0	PARAMETER["latitude_of_origin",0.0]
Linear Unit: Meter (1,0)	UNIT["Meter",1.0]

Geographic Coordinate System: GCS_WGS_1984	GEOGCS["GCS_WGS_1984"
Angular Unit: Degree (0,0174532925199433)	UNIT["Degree",0.0174532925199433]]
Prime Meridian: Greenwich (0,0)	PRIMEM["Greenwich",0.0]
Datum: D_WGS_1984	DATUM["D_WGS_1984"
Spheroid: WGS_1984 Semimajor Axis: 6378137,0 Semiminor Axis: 6356752,314245179 Inverse Flattening: 298,25722356	SPHEROID["WGS_1984",6378137.0,298.257223563]]

Unfortunatelly, this does not seem to be the problem.

Re: Georeferencing points misplaced after import from Link Table

DanPatterson — Wed, 27 May 2020 08:23:11 GMT

What are the actual values of a location and for what location? 2 km is a big difference. 200m would suggest a datum difference, What other coordinate systems are used in your area? I have run out of ideas... what does your associate say?

Re: Georeferencing points misplaced after import from Link Table

GeorgHohberg — Wed, 27 May 2020 10:48:00 GMT

These are some of the values from the link table. In Excell I calculated DX and DY. I find it noticable that the differences between X Source and X Map aswell as Y Source and Y Map are similar in magnitude to the error in the positioning of the map.

X Source	Y Source	X Map	Y Map	DX	DY
442933,5538	4352762,69	446045,758	4350422,3	3112,20386	2340,3818
449572,907	4350765,95	452114,65	4348543,76	2541,74296	2222,19235
445476,2428	4345961,33	448274,215	4343946,74	2797,97238	2014,59736
447174,6206	4345953,34	449935,14	4343867,24	2760,51979	2086,09858
446277,4301	4346276,96	449007,47	4344264,31	2730,03965	2012,65578
442093,9317	4351992,88	445288,386	4349750,92	3194,45459	2241,95361
445759,6246	4341989,77	448716,07	4340025,48	2956,44572	1964,291
444031,8715	4348378,63	447038,966	4346291,02	3007,09424	2087,6092
446004,9766	4349264,23	448906,571	4347095,16	2901,59402	2169,07068
444465,286	4352336,61	447527,427	4349949,36	3062,14122	2387,25015
449300,0961	4341699,96	452029,017	4339853,69	2728,9213	1846,26766
445720,2717	4352941,05	448695,261	4350577,28	2974,98907	2363,77764
448935,2759	4349837,75	451499,85	4347677,44	2564,57382	2160,30782

Re: Georeferencing points misplaced after import from Link Table

DanPatterson — Wed, 27 May 2020 13:30:40 GMT

I have no more ideas, except to revisit the georeferencing. Sorry, the differences are too big to be something simple

Re: Georeferencing points misplaced after import from Link Table

GeorgHohberg — Thu, 25 Jun 2020 09:34:41 GMT

Hey Dan,

after you had run out of ideas, I did no longer pursue this issue until today my collegue send a new link table which he used for georefencing a similar image. It looks like that:

9.543703   2.445142   444393.037816   4340604.876407
10.210346   4.964898   445233.124652   4343248.168412
11.711133   3.523411   446550.556075   4341673.463281
2.363828   7.071456   436840.989781   4345520.312199
10.966851   4.219995   445830.961943   4342445.428037

I can easiely recognize the map coordinates as the correct UTM coordinates. Yet, I do not understand what format the source coordinates are in. Source, target and data frame are set to WGS_1984_UTM_Zone_42N (WKID: 32642 Authority: EPSG). When I set source georeferencing points in the same project as my collegue, I get UTM coordinates. Do you or anybody else have any idea what could have let to the diverging coordinates system that the source coordinates are recorded in in my collegue's project? I am pretty sure that this is related to the original question of this thread.

P.S.: This is what the .prj file says:

PROJCS["WGS_1984_UTM_Zone_42N",GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137.0,298.257223563]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],PARAMETER["false_easting",500000.0],PARAMETER["false_northing",0.0],PARAMETER["central_meridian",69.0],PARAMETER["scale_factor",0.9996],PARAMETER["latitude_of_origin",0.0],UNIT["Meter",1.0],AUTHORITY["EPSG",32642]]

Re: Georeferencing points misplaced after import from Link Table

DanPatterson — Thu, 25 Jun 2020 11:11:30 GMT

the first two columns look like image coordinates unless you are referencing images near the equator and the Greenwich meridian

Re: Georeferencing points misplaced after import from Link Table

GeorgHohberg — Thu, 25 Jun 2020 13:41:41 GMT

Do you have any idea where these come from? Why would the georeferencing tool record image coordinates?

Re: Georeferencing points misplaced after import from Link Table

DanPatterson — Thu, 25 Jun 2020 13:49:40 GMT

From-To points.... ie. this image position is this real world coordinate (row/column to real world)