Overlaying CAD drawing to Google Earth
It has been a while since I posted as i have been out of the survey game for some time but have recently got back in.
I was hoping the community could help shed some light on how to overlay a CAD drawing of a road onto Google Earth.
I am trying to design a new road in Peru in a town called Lobitos. The area in question is shown below (extract from Google Earth).
From Google Maps I was able to pick out the exact road I am designing called Calle La Punta, along with a latitude and longitude of the road in question as shown below:-
I have drawn the proposed road in CAD using Cartesian XYZ coordinates, but these co-ordinates do not in anyway relate to the town of Lobitos in Peru, CAD drawing is shown below:-
How do I align the coordinates of my CAD drawing so they correspond to latitude and longitude values so that I can overlay my CAD drawing to Google Earth?
Any help will be greatly appreciated.
This is a lot of fussy work, but might get the job done. Use some software tool to convert the lat-lon from G.E. for a point of interest to UTM coordinates or other mapping projection and set that as the starting coordinate in your CAD to find the other points' coordinates.
Convert all points UTM to lat-lon.
Make some random points and lines in Google Earth and save them as a .kml (Not .kmz) file to get the format. Edit that file with a text editor to insert your desired lat-lon points.
Open the edited file in G.E.
I've done this process for points in the US using CORPSCON and State Plane Cooordinates. Not sure what conversin tool you would use for UTM in South America.
I was thinking along the same lines as Bill93, convert your Lat/Long to UTM cords. Drop those UTM points into your CAD file and move/rotate your drawing to match those UTM coords. The tricky part is you would need common points in the Google image and your dwg.
I may be over simplifying the process as some sort of scale factor might need to be applied to match Google image, but, in the end, it just seems to be a coordinate transformation but I really don't work with google images, most the the overlays I do are in State Plane.
I do it all the time. Save the image in Google Earth. Google Earth will create a map with a scale bar. Save the image created as a jpg or tiff (whatever format your CAD likes) save it in your CAD project folder.
Go into your CAD Project and insert an image. Pick your insert point. Zoom down to the lower left of the image and you will see the Google Earth scale bar. Draw a line in your CAD that matches the scale bar. Query your line. Divide that distance into the scale bar labeled scale. That will will give you the scale factor. Scale the image by that factor. Move the image by picking a feature you see on the image and snap it to a point on your drawing that is the point on the image. Have your CAD program set the image as background. Then you have to rotate the image a little because your basis of bearing probably isn't the same as Google Earth's. I usually tweak the scale a little to make the image match my CAD as close as possible. And there you have it. Carlson software has a routine that does most of that for you, but I could never figure it out. Clients love it. They can relate to the picture better than you bearing and distance line drawing.
Now tell me what you're going to use the image for so I can tell you if it's an appropriate use or not.
Be careful here if there's any need for real accuracy in this effort. Look at the information here:
Scroll down to the WKT file, the guide for computing coordinates in Google Earth's world. Note the last line in the WKT:
AXIS["Y",NORTH], EXTENSION["PROJ4","+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs"],
This tells you that your lat/lon are calculated on a sphere (note a = b) not an ellipsoid. Note also the write-up and the error possibilities given in the description.
You're not going to be kilometers off, but you'll be far from survey grade. Appropriateness all depends on intended use.