Bathymetry data

Hi,Thank you for your quick response on my earlier query. X Y coordinates of bathymetry data that I have digitized from the navigation map in the GIS are not overlying the georeferenced map created for EFDC. I have adjusted the heading by entering Magnetic declination to get the true north in Google earth while georeferencing the map for EFDC. What should I do to solve this problem? I have attached the screenshot of the problem.

Hi PK,From your screenshot, it seems like the data are offset from the grid. I’ll still check their coordinate reference system first to see if they match, you can also export the grid to shapefile in EE and load them into your GIS software and check the coordinates to see what kind of adjustment is needed to match both of them.

When I export the grid into shapefile and load in GIS software then we can see the grid is shifted to the northwest. I have attached the screenshot. I have bathymetry data for these points in the channel and lake. If I assign these values as bathymetry data in EE, then will it work?

Why the shapefile exported from the EE is not lying over the same area in basemap of GIS?

I wouldn’t suggest you apply those un-matched bathymetry data directly to the grid in EE. Usually, this mismatch between grid and data is because they are in different CRS, thus they won’t line up. But if you are sure that’s not the case, then it would be nice if you can zip up the grid, the grid’s shapefile exported from EE and the bathymetry dataset so we can take a look and have a better understanding of your problem.

Hi,I have attached the zip file as per your suggestion. Thank you very much.

Hi PK,The reason why your grid won’t line up with the background map and the bathymetry data set is most possible cause by bad georeferencing at the very beginning of grid generation. Which means that you probably didn’t line up the background map file correctly when generating the .geo file in CVLGrid, further causing the mismatch.Of course you can try to shift the grid coordinates, but the best approach would be regenerate the grid using a proper referenced background map. The attached figure is a quick example I created showing that grid, base map and bathymetry data can match.Also, when you export the base map from Google Earth (as shown in our YouTube instruction, you don’t need to rotate the map (magnetic declination) since the area you’re working on is relatively small.

Thank you very much. When I avoided magnetic declination correction then my base map and the data were overlapped.