4
  1. I am using qgis 2.8.9 wien version.
  2. windows 10 home 64-bit operating sysytem.
  3. vector layer: Kml file,Line string CRS: WGS 84, EPSG:4326, is the base file for which buffer zone is to mark.
  4. for the need of buffer in meters, I saved the file using "save as" option and saved it as "esri shapefile", where i changed the CRS to NAD 83/Maryland, EPSG:26985. In order to get the buffer zone in meters.
  5. After that selected VECTOR-GEOPROCESSING TOOLS-BUFFERS.
  6. In Buffer option in the slot of "BUFFER DISTANCE", I have filled 1 meter. Because i want the buffer zone of 1 meter, which is shown in below figure: enter image description here
  7. I got the buffer zone in meters but when i cross checked it, it showing the distance of 0.95m. means there is 0.05m error for 1mtr. which is shown in below figure: enter image description here
  8. For 1mtr it is 0.05m error. For 15000m its is showning much more error.
  9. Since i am doing the project of noise modeling. single meter is also important to me.

My question is why this error is occuring? what is the solution for this?

14
  • 2
    Try changing your Projection CRS from EPSG:4326 to EPSG:26985 and try measuring the distance again.
    – Joseph
    Dec 13, 2016 at 11:55
  • Thank you for your reply joseph, I went through your solution but there also i dint get an accurate answer.
    – Khaja
    Dec 13, 2016 at 11:58
  • 1
    Consider also that the Measure line tool is not an accurate way for measuring an exacting distance. I think that the @Joseph's suggest should be the best one to apply.
    – mgri
    Dec 13, 2016 at 12:07
  • 3
    I guess that buffer is computed for each vertex and they are moved perpendicularly compered to the tangent. It may not be extremely exact if there are long distances between the vertices. I suggest to densify the source geometries to have reasonably many vertices.
    – user30184
    Dec 13, 2016 at 12:20
  • 2
    Is the canvas CRS the same as the layer CRS? I see on your screen shot OTF is active!
    – Zoltan
    Dec 22, 2016 at 8:20

1 Answer 1

-2

I'm pretty sure you can't carry out a buffer operation on a kml. Convert to a shapefile first and try that. At the same time convert the projection to a utm form, for instance for Australia EPSG 28355 is a utm.

1
  • OP specified that they already converted to an esri shapefile in a UTM projection.
    – csk
    Oct 30, 2017 at 16:40

Not the answer you're looking for? Browse other questions tagged or ask your own question.