Georeferencing: Difference between revisions
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A case study in georeferencing with ArcGIS 10.3.1 | A case study in georeferencing with ArcGIS 10.3.1 | ||
ESRI's documentation is [http://resources.arcgis.com/en/help/main/10.2/index.html#//009t000000mq000000 here]. | |||
I did georeferencing with old black and white aerial photos a long time ago. Around 2004, so ArcGIS 8.2. | I did georeferencing with old black and white aerial photos a long time ago. Around 2004, so ArcGIS 8.2. | ||
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Scanner settings: full color, 600 DPI. TIFF format. | Scanner settings: full color, 600 DPI. TIFF format. | ||
Here is a scaled down version of the scan for your edification. [[File:eurekamap.jpg]] | Here is a scaled down version of the scan for your edification. [[File:eurekamap.jpg|thumb]] | ||
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== The process == | == The process == | ||
# Scan the map. | |||
# Grab some data to which to tie the scan. Just need roads; also grabbed coastal zones. http://www.humboldtgov.org/276/GIS-Data-Download | |||
# Start ArcMap and create a map with roads and coastal zones. | |||
# Add the unreferenced photo as a layer. Ignore the complaints about it being unreferenced. :-) | |||
# Open the georeferencing toolbar. The photo should already show in there. | |||
# Zoom to the approximate area of the map. (It helps to have it open in a TIFF viewer.) | |||
# In the toolbar, select "Fit to display". | |||
# Pick some nice solid control points, like major highway intersections. | |||
# Using the tools create links from the scan to the vector data. | |||
# I chose "Update Georeferencing" to save the references with the TIFF instead of Rectify which would generate a new image. This also means it will probably only work correctly in ArcMap, and maybe QGIS. | |||
Note that Humboldt county is still on NAD27. NAD_1927_StatePlane_California_I_FIPS_0401 | |||
After doing the georeferencing I think the cartographer pulled the data from the same projection; it only required 3 points to pull it into alignment. | |||
[[Category:GIS]] | [[Category:GIS]] |
Latest revision as of 17:30, 5 September 2015
2015-Sep-03
A case study in georeferencing with ArcGIS 10.3.1
ESRI's documentation is here.
I did georeferencing with old black and white aerial photos a long time ago. Around 2004, so ArcGIS 8.2.
I am trying it with a paper map today, just for kicks. It's a Northern California bicycle map, and it looks almost hand drawn, so I am curious how it will align. I am scanning the Eureka/Arcata area.
Sample image
Scanner settings: full color, 600 DPI. TIFF format.
Here is a scaled down version of the scan for your edification.
The process
- Scan the map.
- Grab some data to which to tie the scan. Just need roads; also grabbed coastal zones. http://www.humboldtgov.org/276/GIS-Data-Download
- Start ArcMap and create a map with roads and coastal zones.
- Add the unreferenced photo as a layer. Ignore the complaints about it being unreferenced. :-)
- Open the georeferencing toolbar. The photo should already show in there.
- Zoom to the approximate area of the map. (It helps to have it open in a TIFF viewer.)
- In the toolbar, select "Fit to display".
- Pick some nice solid control points, like major highway intersections.
- Using the tools create links from the scan to the vector data.
- I chose "Update Georeferencing" to save the references with the TIFF instead of Rectify which would generate a new image. This also means it will probably only work correctly in ArcMap, and maybe QGIS.
Note that Humboldt county is still on NAD27. NAD_1927_StatePlane_California_I_FIPS_0401
After doing the georeferencing I think the cartographer pulled the data from the same projection; it only required 3 points to pull it into alignment.