Re: Map Calibration Using Google Earth


Happy Trails wrote:
On 27 Jul 2006 19:53:58 -0700, miso@xxxxxxxxx wrote:


Happy Trails wrote:
Has anyone had good luck or bad luck doing this? I want to calibrate
images of places far away before I go there.

Are there pitfalls to avoid about which one could be forewarned to
save trouble upon arrival in the area mapped?

Thanks for any comments, pro or con.

- Tom

I'm not sure what you are trying to achieve.

I will explain.

I have a paper map of a place on the other side of the earth from
where I am now.

I will go there in December.

I wish to draw a vector map using this paper map as a background
image.

I will retire in this location, so I don't mind to invest some time in
making some good maps of the area.

I am able to identify places on the paper map and find them fairly
accurately on Google earth because I am familiar with the villages and
street corners.

I want to know if anyone has experience of using known WGS84
co-ordinates, ie from a GPS receiver - tracks, realtime plotting,
whatever, and placing those locations onto Google Earth and actually
being exactly where they are supposed to be.

If the discerpancies are not too great - ie. mere handfuls of meters -
then I will be able to prepare ahead of time my map and it will be
very useful once I am there.

If however others have found that Google Earth appears to be hundreds
of meters out on occasion, or in certain locales, then I will wait
till I go there before squidging/distorting the paper map image into a
correct calibration before doing all my drawing.

The software I would normally use to draw the lines and points for my
vector map doesn't allow this distortion to take place on the lines
and points - only on an overlaid image.

It is a lot of work to do the drawing, and although I would like to do
it ahead of time, I would rather avoid having to do it twice.

Hence my desire to find out from others if the locations reported for
places anyone has visited are actually quite precise - as good as gps
can get them - or if they may possibly be far enough off to render my
work somewhat useless.

Do you understand now?

- Tom

Well, not really. Once you get there, you can make a map using GPS
readings. If this area is remote, I'd just use ExpertGPS since the old
terraserver images are better than google earth in remote areas.
However, I don't even know what country your mystery spot is located,
so it is hard to give any good advice.

I have tried to make maps for off-road driving or hiking from
terraserver images. You really can't tell the condition of the trails
or road from sat images.

I know how to make overlays for google earth. I can make an overlay
using a topo maps that you can overlay on google earth if that would
help you judge the accuracy.

.

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