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I georeferenced a map using grid coordinate and road network shapefile (e.g. intersection vertex) as a control point. I didn't acquire a control point through the survey.

I use "control point (gcp)" to define that point, but my teacher asks me to look for the difference between reference point, control point, and tie point.

Does anybody know the difference?

My book only uses "control point" to define those points.

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You can better understand the difference by taking a hypothetical drone/satellite survey example.

So, in a drone survey, you collect multiple images and process them later.

A tie point is the same point location appearing in multiple overlapped images. These multiple points do not have known ground coordinates, but each has its own image coordinates. A tie point may be a two-ray tie point where it has two corresponding points in two overlapped images, or it can be multiple rays, depending on how many overlapped images are used.

A ground control point (GCP) is a photo identifiable point with known coordinates.

A checkpoint is similar to a GCP but used in examining the adjustment accuracy.

enter image description here

Read the below documentation for in-depth understanding:

https://www.codot.gov/business/manuals/survey/survey-manual-previous-versions/chapter-4/chapter4.pdf

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  • thanks, my conclusion is better to use control point rather than Ground Control Point (GCP) since it mostly used for photogrametry. have u ever seen people use "reference point"?
    – astaga
    Commented Mar 27, 2022 at 17:43

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