Map Processing and calibration with Survey

#1

I am having some difficulty aligning our maps. Our company currently surveys Targets in with high accuracy RTK gps and we then fly the mission and pickup the targets. Our issue lies with the EPSG codes. We do not survey in any particular coordinate system. Local ground coordinates only. Even if we were to use an EPSG code coordinate system some of our jobs are not close enough to published control points to get a baseline for the particular coordinate system. All we need to do is overlay our maps to scale over our surveys in CAD. When you scale the image with 2 control points as expected the map is distorted and the other control points do not fit. The only thing i have been able to do is use the rubbersheet command in Civil3d to manipulate the image based on control point coordinates versus selected points on the images. This works extremely well. 2d maps only of course. but all of our survey points match up with the map image within centimeters. i need to eliminate this Rubbersheeting process in Cad. so my question is…is there a way to calibrate the map in both directions so it is scaled properly to all of the control points. Using only 2d local coordinates? I need this to be done during the processing stage in drone deploy so when i output the image to our drafting department everything overlays perfectly. Some of our survey crews do not even use GPS so it is not possible to get into an “epsg” code system. we need the distances on the processed map between control points to match the measured horizontal distances on the ground…thats it!

thanks!

1 Like
#2

This is something that just about everyone I have spoken with is struggling with and I would suggest a holistic review of your cad workflow and how the drone data is going to be integrated tightly with it.

The correct way to do it is through drawing setup with the correct projection and scale factor information and the TFW file that comes with the orthomosaic will line it up. There shouldn’t be any special functions or plug-ins involved. The two things that are the most common causes are the scale factor from survey, the drawing has been shifted or never started on the correct coordinate system in the first place.

If you would like to share a representative cad file and orthomosaic dataset I would be happy to take a look at it. Just PM me a download link if it is sensitive.

Do you know you’re correct epsg?

#3

Hi Sean

If you post-process (GPS PPK), take a look at EZSurv software, it allow to use local grid projection.
If you know at least 3 points in Lat/Lon/H and their equivalent values on the grid X, Y, Z well you can create a local grid for further post-processing.
Once your local grid is created, GCPs or image position can be computed using your local grid projection. Therefore all output can be made to grid (X, Y H on the grid).