Map Images with Incorrect Position

[JessiecarEsguerra]

Hi GIS Users, I am working a huge number of map images that are already georeferenced.

I would like to know if how I could correct a huge number of images with incorrect position without re-georeferencing.

Is that possible?

[MahtabAlam1]

Please share details about the inputs to help you.

In case you are having georefencing information stored in world files ( ArcGIS Help 10.1 ) then you can easily manipulate them with using python.

Thanks,

Mahtab

[JessiecarEsguerra]

Okay. I have multiple Topo Maps in a raster catalog. These maps are already georeferenced when the raster catalog is created. Upon reviewing, there are number of maps that has incorrect position. I know regeorefencing would address my issue but I don't think it is workable if I have to do it with hundreds or thousand of map images. How did I know that it was incorrect? I overlay it in a basemap and try to review if it will fit in the same location. Location is not that far from the expected position but clients would definitely notice the difference. What I need to know and learn is how I could correct these hundreds or thousand map images without re-georeferencing coz I have a very limited time to do it for the client. Is there a way to resolve this? I would really appreciate if you could help me and share what you know about this.

Thank you so much Mahtab Alam.

[MahtabAlam1]

My thoughts were correcting the world files in case the shift/discrepancy has a contstant factor or even a recognizable pattern. In case you are observing irregular shifts then probably you have to georeference them again.

[JessiecarEsguerra]

Hello Mahtab,

Can you explain it further? How should I correct the world files that you are talking to?

I also wanted to try it to see if this will work.

Also possible ways in correcting it, I would like to try.

Thanks!

[MahtabAlam1]

I am not sure if you are using world files or not. Please refer ArcGIS Help 10.1 and World file - Wikipedia, the free encyclopedia

If you are using them then these are just text files which can be easily manipulated by hand or through scripting. But it will require understanding of the adjustment that needs to be made to correct a particular file. For example Line 5 and Line 6 of world file represent coordinates of the top left corner. You can change these values to find out if this resolves the shift. Off course there are other factors in the world files which impacts the complete translation and it requires their understanding. I am sure the links above could give you the required direction in case you are using world files.

Thanks,

Mahtab

[JessiecarEsguerra]

Hi Mahtab, i'm not using world files but yes I will take a look on the said link and try to understand how i should use it.

[OskarKarlsson1]

Are you certain that there is no projection issues when overlaying those maps over a basemap?

[JessiecarEsguerra]

I Am uncertain on that Oskar. I am thinking that there could be an issue with the projection.

if that is the case, do you know how i could correct this with re-georeferencing each images?

My sample incorrect image is  a Topo Maps in Hawaii. It has Old Hawaiian as th datum. Also, checking in the spatial reference on the properties, it uses Polyconic.​

i am a bit confuse with what's the real issue on these map images.

[OskarKarlsson1]

If you are using ESRI's basemaps, those use WGS84 Web mercator (Auxiliary sphere) projection. If your topo maps use that other projection, you need to find the correct projection transformation for them to overlay correctly.

Do your topo maps align correctly to each other, thus without a basemap?