How to geo rectify the toposheet or autocad file (adding lat and long). I plan to add lat and long to the campus map which is prepared in autocad. How can I add it. By collecting google coordinates or hand held gps co ordinates? Myself I'm having hand held gps 3 to 5 m accuracry. which one gives more accuracey? or any other way to add co ordinates with more accuracy
you can find many tools in arcgis package as well. is better to have GCP from detailed gps survey or good georeferenced images/maps available.
Just georectify and geocode the autocad map with a mother image of the area. or use your GPS to tag coordinates. You may use any image processing software that you have to do thsi process, it is one of the simplest to do.
Dear saif uddin, Haider Al-Ani and all thanks for your response, my doubt is in geocodeing, which one I have to choose for more accuracy either GPS or any other. I'm not having georectified image now, then which I've to be choose...
Assuming the map to be referenced has the correct proportions, there is an easy way to do it in AutoCAD just using the move and scale tools. You will need a well known reference point and the distance between two points in your campus map. The most accurate way is to look for a topographic point (you will have lat, long and height of the point) for referencing purposes. A campus building or sports ground size could be used to scale your map. Using hand held GPS or google coordinates and google distances the method will be the same but you will lose accuracy.
Regards
You can use ArcGIS or ERDAS Imagine, both can provide geo-referenced products with sophisticated geo-referencing tools obviously with spatial error estimation. Good Luck. However, ERDAS Imagine seems better in terms of accuracy.
I think that your hand held GPS will be more accurate than Google coordinates. If you have the possibility to retrieve the RINEX file from your GPS you can try to make a differential solution or at least an ad-hoc processing (e.g. by using the free and open source GOGPS software (http://sourceforge.net/projects/gogps/)) thus increasing the accuracy. Otherwise the only solution is to use a large amount of points into the geo-rectification process. If you don't have ArcGIS or ERDAS Imagine you can use the free and open source GIS QGIS (http://qgis.org/en/site/), the georeferencer plugin is very well done and extremely intuitive to be used.
you can use the GPS coordinates for geocoding the image. It is more accurate than the google coordinates. At the same time, if you want to use google image further for any theme generation, choose google coordinates, otherwise it will give shift ( change of actual positions). The correct method depends on the purpose and future use.
3 - 5 m GPS accuracy is better than Google I'm pretty sure. Also be careful as Google used web Mercator projection, and GPS will give you either straight lon/lat or coordiantes in WGS84. The latter is best to use, unless your campus has a local coordinate system. Last but not least, what are you inputting this into. AutCAD has Map £D that may help w this (been 20 yrs since I used it), QGIS is available for free and ArcGIS for a $99 annual fee. Or do you have a campus license, and if so what?
An alternative is SAFE FME (60 day eval license, not sure of cost) and GDAL routines if you're a geek (I'm not, those are what FME and QGIS use BTW)
I think you can take the GPS points form well demarcated location (top of the building, near a bridge or junction of roads) and then plot them in Google earth, make sure that the points should be well distributed and make triangles, most importantly minimum 4 points should be gathered. Then save the Google earth data and rectify your toposheet easily by any of the topological software (ERDAS, ENVI, ArcGIS, AutoCAD etc.). you can check these videos for reference (https://www.youtube.com/watch?v=LURgkQqnOT4, https://www.youtube.com/watch?v=PHtxbpboDro ). Best of luck.
If you have AutoCAD 3D Map version, then you use the Tools>map tools> rubbersheet option to georeference your plan. Use UTM co-ordinate system so that it will be easier to export to other formats. If you still find it difficult, please approach me. I will do it for you for free.
Cheers.
Sundar Raj
When you start developing the model between image and map/ GPS coordinates, use 1st or 2nd order transformation. Higher order transformation will distort the image non-uniformly.
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