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I've a Brazil road layer that include start km and end km for each road, some are empties. Have checked and some of the values are wrong so I'll calculate road length by myself. I use ArcGis, but can use any other (Qgis, postgresql-postgis).

Original data is in SIRGAS_2000 GCS_SIRGAS_2000 WKID: 4674 Authority: EPSG

Also have available: SIRGAS_2000_Brazil_Mercator WKID: 5641 Authority: EPSG

What's Best Brazil wide reference system to compute road length?

  • Have comapared difference between road lengths calculated between SIRGAS_2000 mercator and SIRGAS_2000_polyconic and ses that differences increas from a 1% starting Latitude 8º S, through 5% at 18 S, 10% in 25 S. – Ferran Ferrer May 31 '17 at 10:55
  • Have checked world azimuthal equidistant and differences more than 5 % are only in Roads going from SW-NE and starting at latitude 8º S increasing towards south. These affects at 10 % of total roads. – Ferran Ferrer May 31 '17 at 11:34
  • I guess Brazil is just too large for one CRS to be (nearly) exact. – AndreJ May 31 '17 at 16:11
  • Look to see if any of the functions/tools you want to use support a "geodesic" option. That'll calculate the distances on the underlying ellipsoid surface. That'll still give "flat" distances--no adjustments for elevation changes. – mkennedy May 31 '17 at 19:08
  • Directly in arcgis, I think that no, but yes working in postgis in geography type geometry can be done. Not sure in ArcGis. – Ferran Ferrer Jun 1 '17 at 9:52

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