I work on QGIS 3.4.4.

My data

I have 4 .tif rasters that will eventually have to be stitched together. The rasters' metadata suggest EPSG:3577 as the initial CRS. I also have a constriction point shapefile having the following coordinates: 1316205E; -2581235N

My aim

Is to make sure the point shapefile sits exactly where the 4 rasters meet and having the CRS same as the initial ones (EPSG:3577).

My steps

  • Set the options for default CRS (see pic below): enter image description here
  • Created the XY point and saved as a .shp with the EPSG:3577 CRS. enter image description here
  • Have used "warp" from GDAL package to project the 4 rasters, with same target CRS as the shp, set the "Output file resolution in target georeferenced units" as 30 (my understanding is that should set the pixels resolution as 30x30m) enter image description here

At the end, the resulting image is as follows: enter image description here

This is with google earth image in the background:

enter image description here

What am I doing wrong?

  • 1
    Sorry for asking the obvious but do you know for sure the given coordinates fall where you expect them to? And did you use warp to reduce the resolution of the rasters from 25 to 30m or were they in a different CRS before? – Techie_Gus Feb 21 at 9:00
  • Adding to what Techie_Gus said...add some Google imagery, transportation or hydrography data and compare that with your imagery to see if the images are drawing in the correct spot. – GBG Feb 21 at 17:41
  • @Techie_Gus <- I am not sure about that. The point shapefile has been provided to me, and am told it's where the pixel corner should intersect exactly. So I am assuming that point over there should sit in the middle of those 4 tiles. The resolution of the rasters is not an issue. Once I make sure I am not mucking around with the CRS, I will deal with the pixel res (which was 25x25 initially). – Overlord84 Feb 22 at 0:27
  • @GBG <- The images look in the right spot, am I seeing this right? (please refer to the post as I have added the aerial image. – Overlord84 Feb 22 at 0:30
  • 2
    @Overloard84 I am not familiar with Australia specific coordinate systems but your images look like they are displaying in the correct space which would suggest that you did that part correctly. The non-aligned point could be because the coordinates were relayed to you with an error or they reference a similar CRS with a different datum. Contact the source of the point data and ask them why it does not display at the intersection of the four images. – GBG Feb 22 at 5:25

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.