Wednesday 23 May 2018

qgis - Determining coordinates of a SHP file


i have a SHP file of a building converted from a DXF file. This SHP file is unprojected and have no specific coordinates (origin 0,0). I find WGS84 coordinates (lat, long) of this building from Google Maps. My aim is to replace these coordinates to the SHP file on QGIS. Could you explain the process step by step?


(I read lots of similar questions, about affine transformation. But i don't know the paramaters.)




What i ask is how to make this transformation in QGIS (step by step)?


SHP file coordinates (not projected)



Scale: 1:142.670.713


X1,Y1: 16.70824, 253.74534


X2,Y2: 1.03521,-6.34918


X3,Y3: 244.00248,-7.49189


Target WGS84 coordinates


X1,Y1: 41.047773, 28.896241


X2,Y2: 41.045452, 28.895929


X3,Y3: 41.045436, 28.899039




I need a second vector layer with coordinates. I have just a SHP file of a building converted from a DXF file. That is not projected. I know where this building is, and can find the WGS84 coordinates from Google Maps. My aim is add WGS84 coordinates to this SHP file and export to replace the building on Google Maps.



My Questions are:


1) I think my SHP file has measurements in meters and unprojected. I have WGS84 lat long coordinates from Google Maps. How can i project this SHP file, for being ready to transformation? Right Click -> Set Layer CRS -> Choose WGS84 EPSG: 4326. Is this enough?


2) qgsAffine plugin just need transformation matrix paramaters. But the answer of @Jochen Schwarze is a bit complex for me. Is there a online calculator? (Just give the source XYs and target XYs and calculate the parameters.)




I think, I have a projection problem before affine transformation. I have a DXF file of a building from AutoCAD. I saved this DXF file as a SHP file in QGIS. But this SHP file is converted from a plain DXF file and is not referenced/projected, it is drawn from coordinates 0,0 in AutoCAD in meters. And the drawing has meters, WGS84 has decimal degrees.


When I set Layer CRS as WGS84 in QGIS, the coordinates don't change.


How can I project this SHP file as WGS84 in QGIS?




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