From time to time I get field data in here that doesn't make sense. Like 7 fence corner shots lying within a 30' radius. These are for utility locations and aren't on a high order of accuracy, but I like to show things as they are. The field crews complete around sixty or seventy a month. Calling them and asking if they remember a fence corner is like pissing up a rope.
My best friend is EarthPoint and Google Earth. Sometimes I insert the aerial underneath my dgn to get the "big picture". That usually requires scaling the image in some sort of SWAG affair until it looks good.
My question to anybody that has more brain cells than I:
The altitude (AGL?) is shown down in the bottom right of the Google Earth screen, along with the lat/ long. Is there anyway to determine an approximate scale of an image from the altitude of the observation?
Ok, I'm a dummy when it comes to things that should be simple. Sometimes I just can't get my head around something.
No. You would need to know the focal length of the camera at a minimum.
Knowing the actual distance between two photo-identifiable points is likely the easiest way to determine scale when the focal length is not known.
Obviously GoogleEarth knows the focal length of the camera, as that's how they are able to compute altitude of the view.
For aerial photography flown with a film camera in the U.S., the most common focal length is six inches. That does not apply to satellite imagery or digital cameras.
If you are running a recent version of C3D you can import into a drawing. If set up correctly it will be geo-referenced reasonably well...
Everybody has a camera these days. Encourage your crews to bring in a few photos from the field. And if you are not already using it field to finish linework helps make sense of these things.
Assuming your data is being collected in a geo-referenced form (SPC's, for example), you should be able to covert your CAD points to a KML file either in C3D, or a program like [REDACTED], and then opened up with the File Open menu pick in Google Earth.
Sounds more like someone forgot to change the descriptor in the DC. First shot was a fence corner and the following 6 shots were something else but they moved on before catching it. I'll further speculate the incident occurred on a Friday afternoon and involved an attractive female coming into view while the work was being completed. :woot: :woot:
I often import georeferenced aerial imagery into autoCAD and as long as it is in real world coordinates and I tell CAD what the datum is, it will sync up fairly well. Also use TBC to generate .kmz files to open in GE but the resolution usually isn't all that great for identifying something small. Another trick I use to use was to import some generic aerial imagery into CAD and just scale it up or down using two known points I can identify in the photo. Definitely not mapping grade stuff but good for the 'big picture'.
Just because I'm paranoid, doesn't mean they aren't out to get me.
Google Eath Pro has some additional tools but not free.
Best alternative I think is to download the free georeferenced orthoimages on the OK GIS site:
http://okmaps.onenet.net/digital_ortho.htm
I believe the GE surface is based on scans from LandSat, the images are georefenced by their respective sources and yes there are some distortions.
Does the local GIS have aerials? Usually better to go to the source (and you can see that GE took the State's efforts for the program)
Just because you see it doesn't make it true
Take a really good look at this image from Google Earth. See anything odd? Follow the white line up the center that is supposed to represent the center of S. Tennessee Ave. Note that the street coming north from W. 2nd St. is to the left of that line, then suddenly gets torn off like a page out of a book. Also note the same street coming south from W. 1st St. is to the right of that line, and also torn off. Note the double vision of some items as is readily apparent in the area of the house to the right of this line and just north of W. 2nd St.
Just because you see it doesn't make it true
It isn't just the street. You'll also note the overlapped ghost images of the buildings to the upper left and lower right of the street in question. This sort of thing happens quite a bit in GE and it's annoying.