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I am trying to georeference a VFR chart in qgis and I can't figure out which CRS to use.

Map projection - Lambert Conformal Conic Projection, Standard Parallels 46.40 and 49.20.

Any ideas which one on the list will work?

underdark
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brink
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1 Answers1

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If the chart shows US location, it's not using a state plane zone, and I can't think of another US-based CRS that has those standard parallel values (46deg 40min and 49deg 20min). With the knowledge that the chart's area of interest is in Canada, I couldn't find any existing CRS that match. I think you'll have to create a custom definition. The central meridian may be the longitude at the center of the map.

Here's a link to the QGIS 1.8 help on projections which discusses creating a custom definition near the bottom of the page.

I don't have QGIS to check this but there have been several other questions here about adding a custom projected coordinate reference system. Cribbing from one, here's a PROJ.4 line for a North American Albers definition:

+proj=aea +lat_1=20 +lat_2=60 +lat_0=40 +lon_0=-96 +x_0=0 +y_0=0 +ellps=GRS80 +datum=NAD83 +units=m +no_defs

Now let's modify it to match yours:

+proj=aea +lat_1=46.66666667 +lat_2=49.33333333 +lat_0=?? +lon_0=-?? +x_0=0 +y_0=0 +ellps=GRS80 +datum=NAD83 +units=m +no_defs

You'll have to fill in the lat_0 and lon_0 (latitude and longitude of origin, try the map's center?).

Padmanabha
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mkennedy
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  • It's actually canadian based over newfoundland. I'll take a look at your link.

    thanks

     – brink May 30 '13 at 22:21
  • Creating your own definition is pretty complex. Any other ideas. I don't have the unix skills to learn proj.4 coding to make my own map projection. – brink May 31 '13 at 21:08
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    You can create "Custom CRS" inside QGIS under Settings. Click on the yellow star, insert a name and the string given above with values for lat_0 and lon_0, and save by clicking on the diskette symbol. Then you find your custom CRS at the bottom of the CRS list. – AndreJ Jun 01 '13 at 05:13