Archive | Solutions to technical problems in GIS RSS feed for this section

How to import an Arcgis raster to Idrisi considering the “NoData” values

19 Nov

Hi again! The conversion between Arcgis rasters such as grids and others to the Idrisi format is fairly simple. However, when you run some of the analyses in Idrisi such as Varcost or to use the Land Change Modeller, you will realize soon that Idrisi gives you an error such as “floating point overflow” and others. This seems to occur when one or more of the rasters you are using have NoData values that are extremely large such as -9999.

The way to solve it is to reclassify your raster either in Arcgis or Idrisi:

1. In arcgis with the reclassification tool delete all the entries leaving only the “NoData” value. Give these values a new value of -1 (for instance)

2. If you have your file already in Idrisi, run reclassify and if you have for instance values of -9999 where in arcgis was NoData, you just Assign a new value of -1 To all values from -9999 To just less than 0.

I hope this is useful for somebody because it took me a while to find the solution to this 🙂

Have a great day!

Error message displayed in the data view

26 Aug

I recently made an sql query with the “select by attribute” tool. An error message appeared in the screen (In data view) and since then I haven’t been able to remove it. This is not only annoying but also really bad as I cannot create any map that do not have the message in it!

I couldn’t find any post about this problem and what I ended up doing was just to transfer my layers from the old project to a new one…

Weird gis behaviour….

Populate a field with consecutive numbers

25 Aug

This is an old problem I encountered some time ago and the solution is rather simple, however to find it  proved to be time consuming so I thought that to share it here would be fine.

I basically wanted to create in an Arcgis shapefile  a field with consecutive numbers. This is easy to do by hand if you have 5 records, but if you have thousands you can find the solution in:

http://resources.arcgis.com/content/kbase?fa=articleShow&d=31374

Enjoy your day 🙂

‘Invalid SQL’ error when using the BETWEEN operator in Arcgis

24 Aug

Ok, so I was basically trying to use a simple SQL operator to select in a  shapefile  polygons that had and “ID” number between 1-1500. It was  impossible for Arcgis 9.3 to understand the common syntax of :

SELECT *FROM soils
WHERE “ID” between 1 AND 1500;

It always returned an error saying that an invalid SQL statement  was used.

After a while thinking about it I discovered that this other form actually works!

SELECT *FROM soils WHERE “ID” >=1 AND “ID” <=1500

I really don’t understand why it doesn’t accept the first form as I think is correct, but anyway, if somebody have the same problem this is a work around… 🙂

%d bloggers like this: