GDP, GNP, and GNI

Here's some help to differentiate GDP, GNP, and GNI from EconomicsHelp.

GDP (Gross Domestic Product) and GNP (Gross National Product) both reflect the national output and income of an economy. The main difference is that GNP takes into account net income receipts from abroad.

GDP (Gross Domestic Product) is a measure of national income / national output and national expenditure produce in a particular country.
GNP = GDP + Net property income from abroad. This net income from abroad includes, dividends , interest and profit.
GNP includes the value of all goods and services produced by nationals whether in the country or not.

GNI
GNI (Gross national Income) is based on a similar principle to GNP. The World Bank define GNI as

GNI is the sum of value added by all resident producers plus any product taxes (minus subsidies) not included in the valuation of output plus net receipts of primary income (compensation of employees and property income) from abroad. (World Bank)

The World Bank now uses GNI rather than GNP.

Since GNI takes into consideration income from abroad, it's unlikely that states collect such data. As a result, states tend to use GDP.