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# Terraserver.com sat images

## Terraserver.com sat images

(OP)
I've been looking at www.terraserver.com 15m/pix resolution photos.  What kind of distortion is there at N 37º Lat?  Can I find the m/degree latitude for 37-38 N and m/deg longitude and assume the photos are streached in the same proportion?  That (I think) gives me 1:1.3 streatch factor.  Could that be right?

BigInch-born in the trenches.
http://virtualpipeline.spaces.msn.com

### RE: Terraserver.com sat images

(OP)
Got it.
Yup.  Gotta' stretch it 1.25 in the N-S direction.

Then it looks like the Googlemap picture too.

BigInch-born in the trenches.
http://virtualpipeline.spaces.msn.com

### RE: Terraserver.com sat images

(OP)
no, the original terraserver looks like the googlemap.  I was comparing to the wrong one.  They both look the same.

Anyway. It appears the 1.25 stretch factor is correct, based on the horizontal, vertical and diagonal distances calculated between the map lat/long coordinates using the NOAA server that calculates dist between 2 pts of known lat & long.

BigInch-born in the trenches.
http://virtualpipeline.spaces.msn.com

### RE: Terraserver.com sat images

(OP)
I compared the stretched version of the sat photo to the airport plan.  They match within a degree or two.

Now the question is why does Terraserver.com sell distorted photos?  Do they take up less space on their servers or something?

BigInch-born in the trenches.
http://virtualpipeline.spaces.msn.com

### RE: Terraserver.com sat images

(OP)
The distorted images may only be characteristic in some areas of the world.  This image of Boston's Logan Airport was not transformed in any manner and the airport plan overlayed exactly.

BigInch-born in the trenches.
http://virtualpipeline.spaces.msn.com

### RE: Terraserver.com sat images

(OP)
This appears to be a problem only with the photos at 15 m/pix resolution.  In N-S direction they are 15, but E-W is 12.

BigInch-born in the trenches.
http://virtualpipeline.spaces.msn.com

### RE: Terraserver.com sat images

(OP)
This is getting worse.

I calculated the distances between the map corners myself, and I do not get the same distances using the usda calculator.  All this could be the result of an error in the usda great circle calculator,

http://www.wcrl.ars.usda.gov/cec/java/lat-long.htm

although that doesn't explain the apparently misaligned runway plan.

Can anybody suggest a known reliable distance calculator based on the W84 Geoid?

BigInch-born in the trenches.
http://virtualpipeline.spaces.msn.com

### RE: Terraserver.com sat images

(OP)
That one is a great site!

pleanty of Excels to calculate distances bwtn lat & long.. lo to hi accuracy.

fixed error in my spreadsheet, so distortions are back in the sat photos, at 15 AND 30 m/pix resolutions

round and round...

BigInch-born in the trenches.
http://virtualpipeline.spaces.msn.com

### RE: Terraserver.com sat images

(OP)
Distortions are everywhere except at the equator.  They use a Mercator (?) projection!  Oslo, at 60N, doesn't look much like Oslo.

BigInch-born in the trenches.
http://virtualpipeline.spaces.msn.com

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