2 replies to this topic

[Robert2009]

How do I extract a feature from an imagery or satallite or DOQQ etc and can I use it in ArcGIS 9.2 ? Do you have suggest a good software or should I stick with ArcGIS ?

[Crischan]

Are you thinking about doing that by hand or trying automatically? If automatically - what kind of feature are you thinking about and what kind of satellite imagery?

For ArcGIS you probably need Spatial Analyst or Image Analyst. ERDAS Imagine would be another software (which works along the lines of Image Analyst) or GRASS if you're happy using a terminal... I have used all, but have done most of my work using GRASS.

[Nikolaj]

Robert,

This is how I would go about extracting a desired feature based on an overhead image.

1st, see if you are lucky enough to have a geoTIFF'ed raster image. The lat/long coordinates will be embedded into a world file that automatically aids in the georeferencing of the image when you add the layer in ArcGIS.

2nd: If the image is NOT georeferenced, you may have to do some intermediate steps using the Georeferecing extension tool in ArcGIS. If you need steps in doing this I will expand. (remember to save your anchor coordinate points after so you can load them later!)

3rd Once the image is loaded into your map view and georefereneced, you will need to zoom to an appropriate extent of the feature(s) of interest that you can visual see. In ArcCatalouge, create a new shapefile, choose the appropriate spatial extent type (point, multipoint, polygon, etc) and if you want to include other attribute information you will add fields at this point. Once it is created, drag or import this .shp file into your ArcMap and ensure that EDITOR extension is toggled. Start an editing session and choose the directory where this .shp file is located. From there you can edit your shape file once it is activated and using F8 you can manually trace/stream via heads-up digitization of polygon boundaries. You can save at differnt points in your individual digitization of objects of the feature class you are making by right click and save part as opposed to save sketch. Once you are done your tracing, save the sketch and continue on if there are more objects of interest before saving your edits.

BTW you can manual insert your attribute information as you are digitizing.

Hope this helps a bit.

Nick