When using EFDC_Explorer and CVLGrid it is often useful to have a background map of the region displayed behind the model. This How-To guide describes the approach to develop these background maps. To create the background map in EE or CVLGrid the following tools are required:
- Google Earth (or similar tool)
- USGS Web Calculator: http://ngdc.noaa.gov/geomag-web/
Geo-reference Map Generation Process
Using Google Earth
The software allows us to generate images and coordinates of determined area.
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- The purpose of determining the Magnetic Declination is to identify the True North for the site. Note that a positive declination is east, while a negative declination is west.
- Run Google Earth
- Type Lake Okeechobee in the search box then select "Enter" key on keyboard.
- On the toolbar of Google Earth, left mouse click on Tools/Options/Apply/OK. Geo-reference Map Generation in EE and CVLGrid and Geo-reference Map Generation in EE and CVLGrid Figure 1 and Figure 2 show this process.
- Add a temporary placemark ( see Geo-reference Map Generation in EE and CVLGrid Figure 3) to get coordinate of the placemark
- Open USGS Web Calculator: http://ngdc.noaa.gov/geomag-web/ ( see Geo-reference Map Generation in EE and CVLGrid Figure 4).
- Copy and paste coordinates of the placemark into the USGS web calculator. Note that select S/N and W/E accurately (see Geo-reference Map Generation in EE and CVLGrid Figure 5 ) then left mouse click on Calculate button.
- Result of Magnetic Declination is displayed in Geo-reference Map Generation in EE and CVLGrid Figure 6.
- Go back the Google Earth, enter the Magnetic Declination 6.26oW (W mean that the Declination here is negative) on the heading of the placemark. (see Geo-reference Map Generation in EE and CVLGrid Figure 7) then left mouse click the OK button. We will see that the background image on Google Earth will rotate from the west to the east with an angle 6.26o.
- After the background image points the true north correctly. Now we can delete the temporary placemark by right mouse click on placemark then select Delete option.
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- On toolbar of Google Earth, left mouse click on Tools/Options/Apply/OK. (See Geo-reference Map Generation in EE and CVLGrid Figure 8).
- Add placemark as names UL and LR
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Figure 12 Choosing Premium resolution.
Using EE
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Note that users can generate a Geo-reference Map in both EFDC_Explorer (EE) and CVLGid. The process for generating the map is same in both tools. |
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- Triangle symbol of Tool Bag on Main Menu of EE then select Bitmap Georeferencing.
Figure 13 Geo-Referencing tool in EFDC_Explorer.
- Click on Setup in the Geo-referencing tool
Figure 14 Geo-Referencing tool in CVLGrid.
- Load the bitmap file (browse to image of Lake Okeechobee, which was generated by Google Earth). The bitmap file is the image file which is called in CVLGrid. The image generated by Google Earth is a JPEG image (*.jpg), so the bitmap file is to be loaded is the JPEG image.
Figure 15 14 Load bitmap file.
- Right mouse click on UL then choose Point 1
- Type the Easting coordinate into X and Northing coordinate into Y
Figure 16 15 Declare UL co-ordinates.
- Right mouse click on LR then choose Point 2
- Type the Easting coordinate into X and Northing coordinate into Y
Figure 17 16 Declare LR co-ordinates.
- After typing coordinates of UL and LR then click Update button
- File/Save Geo-reference File (enter the name and folder location for the geo-reference file) then click Save button.
Figure 18 17 Save geo-reference file.
Figure 19 18 Naming and storing geo-reference file.
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- The geo-reference file named Okeechobee Lake.geo is now generated and can be loaded at any time.
Figure 20 19 Geo-reference file loaded by EE in 2D Planview.