Importing Information From Different Projections to Match the Google Earth Image Placement

[jovivier]

Note: In Version 17 and later you can now set the Datum before importing information from different sources, or exporting to file. The below notes are for Version 16 or older.


When importing background information from different sources, such as a survey DXF/DWG and an automatic Google Earth image, the information can be imported to different coordinate locations because of the different projections used in each file.
It is, however, advantageous to have all information at the same location. Depending on the requirements of the design will determine whether you will move the image or the imported drawing.

Option 1: The client would like to view the design in Google Earth, therefore move the drawing items to the image.
Option 2: Your design will be sent back to the surveyor for marking out, therefore move the image to the drawing.


Option 1: HOW TO MOVE THE DESIGN TO THE CORRECT UTM COORDINATES
1. Look at the location of your design or imported drawing and note down a set of coordinates from the IRRICAD status bar. This is simply to help you find the design after you import the image from Google Earth, as the design and image may seem to disappear if the distances between them are very great.

2. Now in Import from Google Earth locate the property. (Note that the coordinates noted in step 1 have nothing to do with Google Earth or the coordinate system it uses). Import the image without elevations unless they are required. You may receive a warning message about coordinates too large. Click [OK].

3. Turn on all of the layers. If you have trouble locating your design use View|GoTo Coords and enter the coordinates noted in step 1. If you have trouble locating the image turn off all the layers except the “GE Image” layer, Zoom All, and note down some close-by coordinates from the IRRICAD status bar.

4. Select the whole design or imported drawing using Select|Window or similar (do NOT use Select|All) and using Modify|Move move the design closer to the location of Google Earth image. Place the design next to the image.

5. Select the whole design again (minus the image). Using Modify|Move pick a reference point that is easily locatable on the image. Move the design to this point.

Tip: If you have noted the precise coordinates of an item or corner on both the design/drawing and that same location on the image then during Move when asked for a reference point type in the coordinates of the item on the drawing and when asked for an offset point type in the coordinates of the item on the image. Then press <Enter>. Note that if the coordinates of these items were noted in steps 1 and 3 then you can go straight from moving the design from far away to the correct location in one step.

6. The image will most likely be on top of the design. If so, select the image and use Modify|Z-Order|Move to Back and then View|Redraw.

7. Adjust if required by selecting the design items again and moving using a new reference point and offset point as applicable.

8. Now run File|Compress.


Tip: If you receive a warning message about Coordinates being too large after step 8 this will be because you left an item behind when you moved the drawing. Make sure all the layers are on before moving items.

Note: When importing from Google Earth the image is set to true north and at zero tilt. If your imported background’s alignment is not true north you can rotate the design items to match the North orientation.


Option 2: HOW TO MOVE AN IMAGE TO THE IMPORTED DRAWING OR DESIGN LOCATION
If you know the coordinate location of an object in the dwg drawing that coincides with a landmark in the image then you can use direct entry via the keyboard to move the image to the drawing location.
1. Find a common landmark noticeable on the image and the imported drawing. Find, and note down, the coordinates of the location in the imported drawing that the image needs to be placed at. In the image find, and note down, the coordinate location of the landmark.

2. Highlight the image and select Modify|Move.

3. When asked for a reference point enter the image’s landmark coordinates via the keyboard (you will see these display in the far left of the status bar), and press Enter.

4. When asked for an offset point enter the coordinates of the location in the imported drawing and press Enter.
The image will be moved to the correct location to match the imported drawing.

5. Now highlight the image and select Modify|Z-Order|Move to Back and then select View|Redraw.

6. Now run File|Compress.

[jovivier]

Note that these steps have been largely replaced by the Alternate Geodetic Datums option added in Version 17, allowing you to specify the coordinate system or projection that the survey data is in.

The IRRICAD Team