Active Tectonics, Quantitative Structural Geology and Geomorphology

Paper Topo Map to Digital Georeferenced Map in Imagine 8.3

1. Scan map.

Listed are nearby locations:
Scott Blueprint, 833-3912, 133 W 1st Ave., Mesa (used by Holloway)
ICM, 678-1978, 7600 N 16th St., Suite 205, Phoenix (used by Holloway and Stone)
Commercial Blueprint, 967-1400, 20 E 7th St., Tempe
300 dpi grayscale is adequate for 7.5' topo quads. The scans should be in uncompressed tiff format. This produces a ~45 MB image, so bring zip disks. Most places require a pc-formatted zip disk. This can be read with our mac zip drives with no conversion needed. Copy the file onto your MacData folder and retain the zip disk as a backup of the original unaltered image.

2. Rotate image.
Make sure the map is aligned square. To check, zoom into 200-300% along the map border, and scroll side to side and up to down. If the border veers out of view, the image will need to be rotated, which is very likely. Launch Adobe Photoshop (or Canvas). In Photoshop go to: Image-> Rotate Canvas->Arbitrary, then enter the angle of rotation and direction. Angle corrections will generally be from 0.05 to 0.1. Guides are useful to make sure the map is aligned and to judge how much further rotation is needed. To place a guide, zoom to map border, make sure rulers are on, hold the mouse button on the ruler at the top of the image and a horizontal line will be dragged onto the image and placed where ever you let go of the mouse button. The same can be done with the vertical ruler to get a vertical guide. To get rid of these guides go to View->Clear Guides.

3. Crop Image.
The image must be cropped so the upper left hand corner of the topo is the upper left hand corner of the image. Hold down on the Marquee tool in the toolbox (upper left corner, looks like a dashed line box) for more options and select the tool the farthest to the right, it is a thick black box with a diagonal through it. Click on the image and drag open a box on the image. The box size/location can be adjusted by pulling on the tabs on the sides and corners. When the box is in place, double click inside the box and Photoshop will cut off the edges of the image. Guides are useful here as well as the View->Snap To Guides feature.

4. Save image and ftp to Alai.
Once the image is rotated and cropped, make sure it is saved as a tiff file in Photoshop (use the naming convention *.tif). Transfer file from Mac desktop (or MacData) to Alai using Fetch. Start Fetch. Host is, enter your user ID and password on Alai and click OK. Click on binary. Click on Put File. Select the correct filename. Enter the filename you wish it to be saved as on Alai (make sure this is in *.tif format). (It is generally best to keep the same filenames to avoid future confusion). Click OK and watch the little dog run until the file is transferred. A 35-40 MB file will take 2-3 minutes.

5. Import into Imagine.
Log in to Alai. Launch Imagine (Applications->ERDAS Imagine). Click on the Import icon. Change Type menu to TIFF. Change Media menu to File. For input file, click on the folder button and go to the Alai directory where your topo image is located. (For successive files located in the same location, select the Recent button.) Imagine will automatically create an output name as *.img. Click OK. When finished processing, click OK, then close import window.

6. Georeference into Latitude/Longitude.
Open viewer. In viewer box go to File->Open->Raster, then enter the *.img filename and click OK. Go to Utility->Layer Info. Note the width and height in pixels.
In the ImageInfo dialog box, go to Edit->Change Map Model. Change the Projection to Geographic (Lat/Lon), Units to degrees, and enter the upper left X and Y coordinates and pixel sizes. The upper left X is the negative longitude of upper left corner of map. The upper left Y is the positive latitude of upper left corner of map. Latitude and longitude can be entered as DD MM SS and will automatically be converted to decimal form. Pixel size X is 0.125/width in pixels. Pixel size Y is 0.125/height in pixels. Click on OK.
The pixel size equations only work for 7.5' topo quads (7.5' = 0.125deg.). For general use, this can be calculated by using the map scale to convert the resolution of pixels/cm (on map) to pixels/m (on the ground). For example, measure in the X direction 2.5' in inches on the map which equals 6.2 in. Pixel size X is then equal to [(2.5'/6.2 in.)*(1 in./resolution)*(1deg./60')]. If resolution is unknown go to original image in Photoshop->Image->Image Size->Resolution.
In Utility->Layer Info, go to Edit->Add/Change projection. Projection Type: Geographic Lat/Lon. Spheroid Name and Datum Name will be taken off the paper topo map. For Central Arizona quads, it is commonly Clarke 1866 and NAD 27 respectively.
Close and reopen the now georeferenced image.
Place cursor in corners of image and check for accuracy. (X and Y coordinates will be displayed in bottom left of viewer window.) This should be accurate to 0.000. If not, you will have to adjust the upper left hand corner or more often, fudge the pixel width.

7. Reproject into UTM.
Open viewer. In viewer window go to File->Open->Raster, then enter the *.img filename and click OK. Go to Raster->Geometric Correction->Reproject. Toggle Parameters to Projection->Add/Change Projection->UTM. Spheroid Name and Datum Name should be the same as for Latitude/Longitude Projection. Zone is taken from the map. North for Northern Hemisphere. Click OK. Click Apply. Increase the polynomial order (hitting Apply each time) until RMS errors are 0.000000. Click on Resample Image button in the Geo Correction Tools window (tilted shaded square). Click OK. When finished, click OK on Resample Job Status window. Close Model Properties. Save as different output file to distinguish from lat/lon (*UTM.img).
Close and reopen the now reprojected image.
Place cursor in corners of image and check for accuracy. This should be accurate to 10 m. If not, recheck your inputs for spheroid, datum, zone, and hemisphere, or try increasing polynomial order.