topic Re: georeference from paper maps in Data Management Questions

georeference from paper maps

KoushikPaul — Sun, 08 Jan 2012 15:29:42 GMT

Dear Sir/Madam,

I have some paper maps in latitude, longitude and distances in metres. I have already scanned them to my laptop in tiff format. Now i want to georeference them. I am based in India. I have right-clicked on to Layers> Properties. Then in the Data Frame properties, selected Predefined > Geographic Coordinate System> GCS Everest 1830. While georeferencing, I want to enter lat/long values given in the toposheet and have metric units. I have heard that for India, Everest and lambert's conformal conic are used. After I have selected Everest 1830 do I need to again select for Lambert's conformal conic (for example, Projected Coordinate System>National Grids>Indian Subcontinent) ? How to bring metric units?

Koushik Paul

Re: georeference from paper maps

chriss_ — Thu, 12 Jan 2012 02:08:36 GMT

Hi!
Just out of my distant memory to give you an idea
1) Open georeferencing toolbox
2) Use add control point and first click on a known coordinate on your map (e.g. crosspoints of the grid)
second click anywhere else doesnt matter where (just to finsih creating the link)
3) Go to View Link table and change the values of X Map and Y Map to the correct values (The x y values you get from the grid written on your paper map ) of the Links origin point (where you clicked first).
4) Repeat steps for 4 points in each corner of your map
5) Under Georeferencing/Transformation you can choose which transformation you like
6) At the end press Update Georeferencing

Hope that helps you to get started.

Re: georeference from paper maps

KoushikPaul — Fri, 13 Jan 2012 12:31:11 GMT

'
Thanks 'flederfauz' for your reply. But my question was different. You have given me how to do georeferencing. That I know ( since I have gone through 'Introduction to GIS' by Kang-tsung Chang). My question was I have some paper toposheets where the latitudes/longitudes are given and at the bottom the scale is given as 1:50000. I am based in India. Before actual georeferencing, I know I have to choose a Datum and Coordinate system. I have selected Predefined > Geographic Coordinate System> GCS Everest 1830. Do I need to choose Lambert's conformal conic (for example, Projected Coordinate System>National Grids>Indian Subcontinent) also? Because I know that for our Survey of India maps we need to use Everest and Lambert's conformal conic projection. What is the correct method?

Re: georeference from paper maps

MelitaKennedy — Fri, 13 Jan 2012 16:51:47 GMT

If you want to georeference to a Lambert-based India zone, you'll have to get coordinates in that coordinate system that you can use for the georeferencing. One way is to

1. create a text file with the lat/lon coordinates,
2. add it to ArcMap with Add XY data, setting its GCS to use Kalianpur 1937 (which uses Everest)
3. set the data frame to use the India zone,
4. right-click the layer in the table of contents to access data, export data tool.
5. set the tool to use the data frame's coordinate system and save the data as a shapefile or feature class.

Melita

Re: georeference from paper maps

KoushikPaul — Tue, 17 Jan 2012 12:27:05 GMT

Thank you so much, mkennedy. I have now just one unresolved question. Can you just tell me how to make the text file with lat/long coordinates (as you have advised)?

Re: georeference from paper maps

MelitaKennedy — Tue, 17 Jan 2012 18:33:17 GMT

You can make something quite simple through Notepad, for instance. In the file,

ID,latitude,longitude
1,20.0,75.0
2,20.25,75.0
3,20.25,75.25
4,20.0,75.25

The latitude and longitude values must be in decimal degrees, not degrees-minutes or degrees-minutes-seconds.

Melita

Re: georeference from paper maps

KoushikPaul — Tue, 24 Jan 2012 15:46:24 GMT

Thanks, mkennedy; I've been able to do it successfully with your help.

Koushik