Drone image georreferenced in GIS appear wrong in cad

julio_cezarenz · ‎09-30-2019

I have a drone image in tiff format that i did the georreference in GIS but, when i import it to cad,the georreferenced Raster is not the same in GIS. It seens a bit unplaced. What can i do to make the GIS georreference fit to cad georreference?

CodyBenkelman · ‎09-30-2019

Julio

Can you please provide more detailed information? It is difficult to offer advice based on your description above.

1) how did you perform the georeferencing? Using the Ortho Mapping tools in ArcGIS Pro? Using Drone2Map? Or using the Georeferencing tools?

2) What version of our software did you use? ArcGIS Pro 2.4 or earlier version? ArcMap 10.7.1 or earlier? Drone2Map 2.0 or 1.3.2?

3) If you used the Georeferencing tools, did you use "Save" or "Save As"? "Save" creates a separate georeferencing file that will not be recognized by CAD software. "Save As" resamples the input image to create a new image, which should work properly in CAD, but the image quality is reduced slightly.

4) when you say "It seems a bit unplaced" do you mean it's in the right area but a few meters from the correct position? 25 to 100 meters? Or is it in completely the wrong location? If the incorrect position is 25-100 meters, this may be a problem with the datum (NAD 27 vs. NAD 83 etc.)

Cody B.

julio_cezarenz · ‎10-01-2019

Cody, thanks for reply. I did the georreferencing using Arcgis Desktop 10.6. When i finish the process, i run the "Update georeferencing". Then i rename the tfw to tfwx so, in theory, it can be recognized by CAD. But when i make the "Map Insert" command in CAD (AutoCAd civil 3D 2016) with the same SRC as GIS, the tiff image shows up with no the same georreference as in GIS. The drone images was processed using PhotoScan software. I am sharing with you some prints that show the diference i am telling you. Thanks.

PavanYadav · ‎10-01-2019

Hi Julio,

World files (tfw) don’t carry all Spatial Reference information, please see: http://desktop.arcgis.com/en/arcmap/10.3/manage-data/raster-and-images/world-files-for-raster-datase... . Not sure, if AutoCAd civil 3D can read the Spatial Reference information stored in the headers and/or aux or aux.xml files. Spatial Reference information is more important if you AutoCAd civil 3D map/layout is one Spatial Reference (e.g. GCS North American 1983) and your Georeferenced Image is a different Spatial Reference (e.g. NAD 1927 UTM Zone 1N). Now, you will have to apply an appropriate datum transformation, if it’s available in AutoCAD, please see: http://desktop.arcgis.com/en/arcmap/10.3/guide-books/map-projections/choosing-an-appropriate-transfo.... If you don’t apply a right transformation, you may see some shift.

So, you might want to check a couple of things:

Your image’s Spatial Referenc
Your AutoCad Maps/layout’s Spatial Referenc
Apply a right transformation if necessary

If using a World File, make sure it was using for the same Spatial Reference that you have in AutoCAD.

Hope this helps.

Regards,

Pavan

CodyBenkelman · ‎10-01-2019

Julio

I'm unclear on what processing you applied in ArcMap 10.6. Your imagery should have been accurately georeferenced after processing in Photoscan.

Can you clarify this:

1) do you have ground control points that you're using in Photoscan?

2) you say "A drone image". Do you mean "an orthomosaic that Photoscan created (from many drone images)"...? Or do you mean one single drone image?

Cody B

julio_cezarenz · ‎10-01-2019

I have a shapefile with the control points that i used to make the georreference in GIS, so we not set the ground controls points in Photoscan. The image i mean is a orthomosaic created from 1,000 images.

Thx.