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As mentioned on our home page, we have a great deal of experience in data conversion. The thoughts on this page are by no means all of your choices but merely brief discussions of a variety of methods. We have digitized entire western U.S. Indian reservations from typical map sources such as USGS 24k and 100k quad sheets, countywide parcel maps and VERY nontypical sources such as a single large map drawn by hand on cloth around 1910. That particular map was in support of a tribes' litigation for water rights. We've done countless other smaller projects over the years and are expert in seamlessly tiling and edgematching your data for maximum usefulness and appearance. This is where small details mean alot further down the process of creating and attributing feature data. Digitizing has generally gone by the wayside as a form of acquiring data because there is so much functional data already in existence for most applications and digitizing is extremely time and labor intensive. However, on certain occasions such as parcel maps, digitizing may be the best method to get your original data into a GIS database. There are other forms of data conversion such as scanning source maps then transforming them into real world coordinate systems. We can layout your options and help you decide what is the best and most cost effective to get your data as accurate as possible in a GIS. Heads up digitizing from imagery is also an efficient, accurate (depending on the operator) and comparatively quick method of quickly creating GIS layers. The most common source of imagery to digitize from is orthophotography because is it highly accurate and typically has a high resolution, 6 inches to 2 feet, but satellite imagery such as that from Digital Globe are also excellent sources to digitize from. Either product is a good choice to capture building footprints also. A word about data created in CAD systems and conversion costs... ??????? Many shops use their CAD personnel to create data files before sending the files over to the GIS side of the operation for attributing and further work. This is SOMETIMES a cost effective means of creating GIS data but not always for the following reasons... For example, CAD systems don't typically care about how many vertices make up a particular curve or line feature where GIS software normally processes individual vertices and nodes as part of the features. See figure 1 below for an example of CAD data converted into ArcInfo. Do you really need this many vertices to define this curve? Of course not! It is certainly common to simply run a 'clean' operation on a coverage but using a blanket command like that sometimes has unintended consequences such as reshaping some features and having some features jump as well. Having many hundreds or thousands of extraneous vertices, in particular, drastically slows down the drawing time of a coverage and uses far more cpu time than it should. Ever refresh or resize your window and wait and wait and wait while the little globe on the bottom of the ArcGIS frame spins around? Bad data like this may be the culprit! Fig. 1 Another artifact of CAD data are duplicate vertices and vertices that far too close together to be of any practical use. Figure 2 shows the glaring red noderrors associated with this type of artifact. Figure 3 demonstrates duplicate vertices that occur throughout the line files created in CAD software. Fig. 2
Fig. 3 Figure 4 shows one more fine example of bad CAD data although this example is more inexperienced operator error than software error. The distance from top to bottom of this view is about 0.4 of a foot. Extraneous short segments like this one make it very difficult to get addressing software to work correctly and simply adds more useless junk to the file for slower processing. There's no excuse for this type of data!! Fig. 4 When looking at single examples of these CAD artifacts, they may not seem like much by themselves, however, when you add up the thousands of extra vertices and node errors in the typical road centerline or parcel coverage created in CAD software, they are VERY significant because this will noticeably slow down your processing. At Sandia GIS we have been using and converting CAD data for many years and we will NOT let this type of artifact slip through the cracks and be delivered to you. We absolutely know how to deal with and clean up these types of CAD artifacts so you will have the cleanest, most efficient data. We can also go through your existing data and clean up leftover garbage like this so you have the cleanest data with the smallest file size possible. |
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