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Geometric Correction of Satellite surface imagery

flowengr
Explorer

Geometric Correction of Satellite surface imagery

flowengr
Explorer
Explorer

I am using AutoCAD LT, attaching satellite jpeg images, then drawing on an overlay on the image. There are length errors in both the x and y plan. Is there a process that improve accuracy?

The possible errors are many: sloping terrain, angle of the eye, etc.

  • Are some image file types better than others?
  • Is there a process to normalize the image?
  • How does accuracy of satellite imagery compare to aerial photography?
  • Are there ways to check whether an image copied from GE spans a seam between adjacent images, which might introduce a new set of distance errors?
  • Can anyone recommend a good reference on techniques to improve drawings that are based on overlays f satellite imagery?

Thanks for any help you can offer.

Russ

 

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pendean
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So how did you acquire those JPEG images exactly? source, method, etc.

Any reason you don't want to use the GEOMAP command/options built into LT to do what you need? Look up usage in HELP.



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ChicagoLooper
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Satellite imagery is not typically georeferenced against a projected coordinate system (think cartesian coordinates) like State Plane or UTM zones, which use units of feet and meters, respectively. They are frequently referenced to a global geographic coordinate system, as in lat/long, like WGS84, which uses units of degrees. 

 

As you already know, ‘attaching’ a satellite jpeg requires you to size the image using the scale command and orientate to north using rotate. To do this, however, requires you to use ‘known’ reference points in the image so you can accurately scale and rotate. Simply using scale and rotate in Acad LT without known reference points is where errors occur. (Known ref points=lat/long or northing/easting or coordinates in feet or meters.)  Not mention the amount of points you use—two points minimum but using more will invariably increase accuracy—the more points you use the better. 

 

If your reference points are in lat/long then you’ll likely need to transform them from degrees to your modelspace  drawing units of either feet or meters and that’s not easy, nearly impossible, using just AutoCAD LT.  

 

AutoCAD Map 3D and Civil 3D both have the geospatial capabilities to handle satellite imagery, Acad LT, not so much. M3D/C3D can not only scale and rotate but can also geolocate the image the correct x- and y-distance from 0,0,0, or the origin, due to the program’s built-in Coordinate System library. 

 

Acad LT is OK, but if you want to do something like get ‘accurate’ scale on satellite images, you’ll need more horsepower. 

 

 

Chicagolooper

EESignature

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flowengr
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Solución aceptada

Thank you for the suggestion. I was unaware of the GEOMAP command.

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flowengr
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Very helpful. I am glad to know more about comparing capabilities between LT and the more upscale civil packages. For now, I'll continue to use LT. I am still processing your many comments. Thank you for your generous comments.

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