I have a number of aerial images that do not align with where my GPS says I am. For example, I am standing at the intersection of two roads with a Trimble R10 and a handheld IOS device with the aerial imagery as a geotiff displaying on it. The highly accurate GPS position is saying I am in the ditch about 6m away on the imagery. To rectify the imagery alignment issue I seem to be having I would imagine some program of placing Ground Control Points is necessary. My question is, how do you do this for aerial imagery that is already existing, not being flown at time of GCP collection. I know I need to find easily identifiable features on the aerial image but (1) I am in the middle of no-where and easily identifiable features are at a premium and (2) I will have to manually choose where I think the feature is on the image which could be off by up to, even over a meter thus defeating my Trimble's high accuracy. I think I am approaching this the only way you can, but want to see if there are different thoughts on the topic.

Trimble R10 Model 2 - (https://www.duncan-parnell.com/storage/attachment/datasheet_-_trimble_r10_model_2_gnss_system.pdf)

  • Seems to me this is due to how the image was georeferenced to begin with. Either it wasn't properly done, or another factor is making the specific spot you are checking misaligned. Depending on the method used, some areas in the image might be worse than others. Have you tested other areas? Do you have access to the original image and the parameters that were used to geoerefence it? – Gabriel C. Apr 10 '19 at 15:49
  • No, I don't have access to the original data nor how it was georeferenced. The mis-alignment is variable but seems to be between 3-10m – D_C Apr 10 '19 at 15:56
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    Then, if it's critical to your task, I suggest trying to georeference it yourself using another source of better georeferenced imagery like a WMS service. It shouldn't be too hard but this is dependent on spatial resolution, I guess. – Gabriel C. Apr 10 '19 at 16:04
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    What correction service is the R10 using? The Trimble network? Are there trees or power lines overhead? How's the sky view? – mkennedy Apr 10 '19 at 16:18
  • I am going to research WMS service now. I am trying to find as many power poles as possible. The imagery is good (30cm) so I can pick them out when they are around. I am trying to put the GCPs in the open on, or just off, roads. In places where I don't have power poles, I am using the intersection of roads or other features that are leading up to the road (e.g. recreational trails). – D_C Apr 10 '19 at 19:00

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