2

I'm trying to make a South American topography map based on SRTM data on QGIS. The problem is a visual one. If the topography contours are extracted from individual SRTM tiles, it results a little straight line connecting each curve from both tiles. If the tiles are merged before and then the curves extracted, it doesn't happen. The ideal would be merge all tiles from South America and then extract the contours, but the program or my computer doesn't handle the process. The archive is too large I guess. It seems not a big problem, but in the end the visual impact of these lines turns to be evident in a larger scale. So:

  1. Is there another way of avoiding these connecting lines from each tile?
  2. If not, can I delete then in a faster way than node by node?

figures

  • Building a vrt out of the source rasters should avoid the memory problems you may run into. – AndreJ Oct 15 '15 at 3:50
  • It's really hard to see what the problem is from that screen shot, perhaps try again with a darker and thicker line. Some sort of focal smoothing may help but might also damage the data so a bit of experimentation is called for - perhaps make a band of cells from the focal mean 5x5 covering the area and insert it to mask the bad cells. It is not uncommon for elevations to differ slightly between tiles and in flat areas that can be quite evident in the contours; if the difference is uniform it may be that one tile is in a different height datum - but it's hard to tell from here. – Michael Stimson Oct 15 '15 at 5:11
  • Looking at the example image you have given they appear to be the same size and possibly not part of the true contour line? If this is the case can you not simply select the polylines that are Xm long and delete them? – Hornbydd Oct 15 '15 at 9:34

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.