How do I convert irregular lat/lon data from excel to a regular MATLAB grid for viewing as a contour plot?

Hey there... I have a large data set with 6 columns in excel ordered by lat/lon (in decimal degrees to 0.01) and other variables such as year, month and most importantly for my survey, trawler fishing time in decimal hours. I want to build a 0.01 by 0.01 degree grid in MATLAB and view density of fishing hours (values between 0 & 8 hrs) as a contour plot. I have limited experience with MATLAB, I can make a grid using meshgrid to the appropriate size (58 x 165 grid cells) and I have imported the excel column data as vectors and as an array. How do I transpose/convert my data to a grid? There are multiple entries in the data for some grid cells and none for others. Help would be greatly appreciated.

Answer 1

[Chad Greene]

Try using gridfit.

However, a note which you may wish to consider or neglect, depending on the level of accuracy you need: Be aware that 1 degree of latitude is not the same distance along the ground as 1 degree of longitude. Depending on where you are, the effects of gridding under the assumption of equal distance can be negligible, or can become significant.

[Eoghan Daly]

Thanks for the suggestion Chad. Unfortunately it doesn't seem to do what I want. It interpolates values where there is no data and for my project I need to have zero or NaN values where no fishing took place. I think my problem is an indexing one, where I need a piece of code to recognise and assign Z values from my data to a regular XY grid while combining multiple values if found for one XY point and assigning NaN where no entry exists for a given XY point. I can easily do it manually in excel except there are 75 K rows of data.