I’m new in Arcgis, and I have some trouble in this task: I downloaded from ICC (www.icc.cat) a raster data map that is a in a specific coordinate system, if I right click to view its properties, it says:

spatial reference : ETRS_1989_UTM_Zone_31N.

but it says nothing about projection reference so if I try to do a Define Projection it warns me that I have one defined and nothing happens.

On the other hand, I have a gpx file with data extracted from a GPS and I found a geoprocessing tool that converts gpx into features. Once I have it converted and situated in my data frame, I can see that the Projected Coordinate system is:

Geographic Coordinate System: GCS_WGS_1984

So, the raster data map and the vector data points does not match on the screen.

Trying to solve this problem, I used a Project tool to convert from GCS_WGS_1984 coordinate system to ETRS_1989_UTM_Zone_31N the vector data, but map and track still don’t match. If I zoom to layer the map is in one site of the screen and if I zoom to layer the track, is in the other site.

I tried different thinks but I cannot succeded on match the data on the screen. I also created another dataframe with an empy projection defined and inserted the map and the reprojected track, but I still have the same problem.

Can someone tell me what I’m doing wrong?

Raster Data RasterData

Vector Data VectorData

  • What version of ArcGIS are you using? – Midavalo Apr 16 '16 at 19:00
  • ETRS_1989_UTM_Zone_31N is a projected coordinate system, using the Universal Transverse Mercator projection. So the projection is already defined, hence the warning that you have one defined. On the other hand, GPS works on the WGS84 geographic coordinate system. So all GPS devices essentially operate on WGS84, and GPS coordinates in any other system are either projected or transformed. It would help if you could indicate the measured shift between raster and vector. For some background on ETRS and WGS killetsoft.de/t_1009_e.htm – Techie_Gus Apr 17 '16 at 6:44
  • Please include the extents of both layers plus the location they're supposed to represent. You might need to do it in two different ArcMap sessions. – mkennedy Apr 17 '16 at 12:53
  • Hi!! thanks for your replays. I attached screen captures with more information. I hope it is useful for you to see what is wrong. – aniger33 Apr 17 '16 at 19:42
  • It seems to me from the extent of the raster data shown that there is something wrong there. Usually, easting in UTM coordinates start with a value of 500000 while your data set shows a weird extent. I would recheck your raster data, as your vector data look ok to me. I have a feeling the raster is not properly georeferenced and the extent you see is just pixel coordinates. – Techie_Gus Apr 17 '16 at 21:28

Thanks all for your responses, they are the clues for me to realize what was happening.

First think to notice is that when I drag and drop the raster into the dataframe in Arcmap, it pops up an alert saying “Unknown spatial Reference”, that means this raster map was not referenced and hasn’t a defined a projection. Assigning a projection to the dataset is not a solution. The map needs to be georeferenced to a specific projection, and then, one could change between different projections.

Another thing to realize, as you has mentioned, is that the visible extends of the map are very weird. We can see that top and left values are near zero. This is because it has not a projection defined and arcmap don’t know where to place it, and it does where latitude and longitude are zero, a point situated into the sea near Africa. We can see this adding a world base map into arcmap and zooming out our map.

enter image description here

So the solution to have this map georeferenced is using the Georefence Toolbar in arcmap, and use another source of reference, for example a georefereced base map, to relate ground control points. More info info about this can be found googling.

Ex: https://mannlib.cornell.edu/files/documents/ArcGIS_Georeferencing_An_Image_v10.0.pdf

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