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ColinD

2,050 post(s)
#12-Sep-22 01:27

Imported 20 .asc files and each came in as GDA94 / MGA zone 55 (EPSG:28355). Created a map containing all set to the same projection. Merged all 20 (dialogue showed the same projection) and exported as .asc. Imported into M8 and they are now UTM - Zone 31 (N) requiring the correct projection to be assigned. Is this user error somehow?


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Dimitri

7,090 post(s)
#12-Sep-22 06:02

Imported 20 .asc files and each came in as GDA94 / MGA zone 55 (EPSG:28355). Created a map containing all set to the same projection. Merged all 20 (dialogue showed the same projection)

Need all the details. Did you import into 8 or into 9? .asc files do not provide projection info, so how was it the initial projection was assigned? Were there any side car files such as world files, .prj files, etc? When you created a map, how did you do that and what was the projection used by the map? When all were "set to the same projection" how did you do that and what projection did you use? How did you merge all 20, what projection did you use, etc. When you exported, what sidecar files were created? etc, etc. This is all a matter of details, so to understand any inconsistency you have to drill into each and every detail.

adamw


10,175 post(s)
#12-Sep-22 10:20

Well, MGA zone 55 is quite far from UTM zone 31 -- they both are transverse Mercator, but the center meridian is 147 for the former and 3 for the latter. So, no, this isn't good. But as Dimitri says, need details. It's hard to say what went wrong without knowing what was happening in general. (Did export from 9 produced a PRJ that 8 misread?)

ColinD

2,050 post(s)
#12-Sep-22 12:36

Sorry about the sparse report.

I've attached one of the DEM and associated prj along with the two prj that are produced by 9 when exporting as asc. Imported the 20 asc into 9 and the default projection shown was GDA94 / MGA zone 55 (EPSG:28355). Created the map in 9 containing all 20 rasters and changed the default of lat/lon to EPSG:28355. Merged in 9 using Edit/Merge then exported as asc and imported into 8 where Assign Projection was needed to get back into the southern hemisphere.

Attachments:
DEM_2m.prj
DEM_2m.wkt.prj
Gulgong201510-LID2-AHD_7726414_55_0002_0002_2m.asc
Gulgong201510-LID2-AHD_7726414_55_0002_0002_2m.prj


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adamw


10,175 post(s)
#13-Sep-22 09:59

OK, that helps. Exporting to ESRI GRD (the name of the format for the ASC file) creates a PRJ file that contains not the traditional PROJCS[...] data that everyone is accustomed to, but rather the ArcINFO projection data. The ArcINFO projection data is rather limited and is not enough to re-create the projection. The export also produces a file with the traditional PRJ data: xxx.WKT.PRJ. But 8 doesn't load that file until you get rid of xxx.PRJ and rename xxx.WKT.PRJ to xxx.PRJ. Alternatively, you can load the projection from xxx.WKT.PRJ manually in the 8's coordinate system dialog. Now what is really puzzling is that 8 does not seem to be able to read data in the xxx.WKT.PRJ either. We are currently investigating why, will get back with the results.

ColinD

2,050 post(s)
#13-Sep-22 20:11

Thanks!


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