Image Calibration

rbrown3rd · Post by **rbrown3rd** » Wed May 04, 2005 9:41 pm

I use a lot of aerial images for direct digitizing of polygons. I have always inserted them as maps and have calibrated quickly and easily by entering the upper left and lower right coordinates by cutting and pasting values from a text file I have for each image. In old versions of Sbuilder it was a simple one step process. Now I have to enter the coordinates and hit the ok button twice and sometimes three times bofore I get a calibrated image. I usually have to delete the map that was inserted and do it again. Am I doing this wrong? Has the procedure changed?

Luis Sa · Post by **Luis Sa** » Thu May 05, 2005 6:22 am

Hi,

I tried to make calibration more flexible. Before you needed a NW and a SE point. Now you can have for example a NE and a SW point.

But if you know the borders you just enter them either in the map properties window or in the left boxes of the calibartion windows. In this last case you do not change the right boxes (that contain the limits of the map in pixels).

With the present interface I normally do the following. Append a GPS map. Place the map. Enter calibration. Press "lat1/lon1" button and click a point on the GPS map so that the coordinates are taken by SB. Then press "pixelX1/Y1" button and click the corresponding point in the bitmap (not in the GPS map). Do the same for Point #2 and "Calibrate".

If you can get a GPS map for the region you are working, this is the fastest and precise way to calibrate bitmaps.

Regards, Luis

PS: there was a bug that I corrected (see the forum and the problems that Dick was trying to explain to me). May be this is the cause of your problem. I will upload the new version as soon as I finish the Help file.

rbrown3rd · Post by **rbrown3rd** » Thu May 05, 2005 6:35 am

Thanks Luis. I export images from Expergps along with a little text file with the NW and SE corners automatically. That text file is the one I use to grab the two corner coordinates. It worked great before but not so great now. Maybe your update will fix it. Thanks so much.

rbrown3rd · Post by **rbrown3rd** » Mon May 09, 2005 7:17 am

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Luis Sá
 Hi,

I tried to make calibration more flexible. Before you needed a NW and a SE point. Now you can have for example a NE and a SW point.

<hr height="1" noshade id="quote"></blockquote id="quote">
That worked fine for me Luis. I just had to change my methodology slightly. I click close to the upper left corner which gives me a pixel location and then I edit it to 1 and 1. The program then seems to get the maximum limits of the map/image automatically. That works for me. Thanks for your excellent explanation of how to do it.

rbrown3rd · Post by **rbrown3rd** » Tue May 10, 2005 5:10 am

That works great now that I am used to it. I finally see that the software defaults to the limits of the image. That is terrific. I have no problems now and like the new way better than the old way. Thanks very much Luis.

Luis Sa · Post by **Luis Sa** » Tue May 10, 2005 6:26 am

Yes,

There was a calibration problem which Dick pointed out! It should be OK with the "oficial" release.

I am happy that you find the calibration more easy. It was the result of my own experience when I used SBuilder to create Portugal Terrain. There was no reason, for example, that the 2 points should be NW and SE! Sometimes you have data for a NE and a SW point!

Thanks, Luis

rbrown3rd · Post by **rbrown3rd** » Tue May 10, 2005 7:02 am

Very true Luis and perfectly logical. I agree that the new method is more flexible. I just did not understand how easy it would be to calibrate with the extreme corners. I am delighted that the software discovers the size of an image and defaults to the 0,0 and the 0+x,0+y coordinates because those are the ones that my software generates. The fact that it could also be any two points is even better. Like money from home without asking for it. [:)]